Re: [RfC PATCH] Add udmabuf misc device

[Daniel Vetter]

Ok, confusion around backend is I think cleared up. The other
confusion seems to be around dma-buf:

dma-buf is the cross subsystem zerocopy abstraction. PRIME is the
drm-specific support for it, 100% based on top of the generic struct
dma_buf.

You need a dma_buf exporter to convert a xen grant references list
into a dma_buf, which you can then import in your drm driver (using
prime), v4l, or anything else that supports dma-buf. You do _not_ need
a prime implementation, that's only the marketing name we've given to
dma-buf import/export for drm drivers.
-Daniel


On Mon, Apr 16, 2018 at 12:14 PM, Oleksandr Andrushchenko
 wrote:
> On 04/16/2018 12:32 PM, Daniel Vetter wrote:
>>
>> On Mon, Apr 16, 2018 at 10:22 AM, Oleksandr Andrushchenko
>>  wrote:
>>>
>>> On 04/16/2018 10:43 AM, Daniel Vetter wrote:

 On Mon, Apr 16, 2018 at 10:16:31AM +0300, Oleksandr Andrushchenko wrote:
>
> On 04/13/2018 06:37 PM, Daniel Vetter wrote:
>>
>> On Wed, Apr 11, 2018 at 08:59:32AM +0300, Oleksandr Andrushchenko
>> wrote:
>>>
>>> On 04/10/2018 08:26 PM, Dongwon Kim wrote:

 On Tue, Apr 10, 2018 at 09:37:53AM +0300, Oleksandr Andrushchenko
 wrote:
>
> On 04/06/2018 09:57 PM, Dongwon Kim wrote:
>>
>> On Fri, Apr 06, 2018 at 03:36:03PM +0300, Oleksandr Andrushchenko
>> wrote:
>>>
>>> On 04/06/2018 02:57 PM, Gerd Hoffmann wrote:

   Hi,

>> I fail to see any common ground for xen-zcopy and udmabuf ...
>
> Does the above mean you can assume that xen-zcopy and udmabuf
> can co-exist as two different solutions?

 Well, udmabuf route isn't fully clear yet, but yes.

 See also gvt (intel vgpu), where the hypervisor interface is
 abstracted
 away into a separate kernel modules even though most of the
 actual
 vgpu
 emulation code is common.
>>>
>>> Thank you for your input, I'm just trying to figure out
>>> which of the three z-copy solutions intersect and how much
>
> And what about hyper-dmabuf?
>>
>> xen z-copy solution is pretty similar fundamentally to
>> hyper_dmabuf
>> in terms of these core sharing feature:
>>
>> 1. the sharing process - import prime/dmabuf from the producer ->
>> extract
>> underlying pages and get those shared -> return references for
>> shared pages

 Another thing is danvet was kind of against to the idea of importing
 existing
 dmabuf/prime buffer and forward it to the other domain due to
 synchronization
 issues. He proposed to make hyper_dmabuf only work as an exporter so
 that it
 can have a full control over the buffer. I think we need to talk
 about
 this
 further as well.
>>>
>>> Yes, I saw this. But this limits the use-cases so much.
>>> For instance, running Android as a Guest (which uses ION to allocate
>>> buffers) means that finally HW composer will import dma-buf into
>>> the DRM driver. Then, in case of xen-front for example, it needs to
>>> be
>>> shared with the backend (Host side). Of course, we can change
>>> user-space
>>> to make xen-front allocate the buffers (make it exporter), but what
>>> we
>>> try
>>> to avoid is to change user-space which in normal world would have
>>> remain
>>> unchanged otherwise.
>>> So, I do think we have to support this use-case and just have to
>>> understand
>>> the complexity.
>>
>> Erm, why do you need importer capability for this use-case?
>>
>> guest1 -> ION -> xen-front -> hypervisor -> guest 2 -> xen-zcopy
>> exposes
>> that dma-buf -> import to the real display hw
>>
>> No where in this chain do you need xen-zcopy to be able to import a
>> dma-buf (within linux, it needs to import a bunch of pages from the
>> hypervisor).
>>
>> Now if your plan is to use xen-zcopy in the guest1 instead of
>> xen-front,
>> then you indeed need to import.
>
> This is the exact use-case I was referring to while saying
> we need to import on Guest1 side. If hyper-dmabuf is so
> generic that there is no xen-front in the picture, then
> it needs to import a dma-buf, so it can be exported at Guest2 side.
>>
>> But that imo doesn't make sense:
>> - xen-front gives you clearly defined flip events you can forward to
>> the
>>  hypervisor. xen-zcopy would need to add that again.
>
> xen-zcopy is a helper driver which doesn't handle page flips
> and is not a KMS driver as one might think of: the DRM UAPI it uses is
> just to export a dma-buf 

Re: [RfC PATCH] Add udmabuf misc device

[Oleksandr Andrushchenko]

On 04/16/2018 12:32 PM, Daniel Vetter wrote:

On Mon, Apr 16, 2018 at 10:22 AM, Oleksandr Andrushchenko
 wrote:

On 04/16/2018 10:43 AM, Daniel Vetter wrote:

On Mon, Apr 16, 2018 at 10:16:31AM +0300, Oleksandr Andrushchenko wrote:

On 04/13/2018 06:37 PM, Daniel Vetter wrote:

On Wed, Apr 11, 2018 at 08:59:32AM +0300, Oleksandr Andrushchenko wrote:

On 04/10/2018 08:26 PM, Dongwon Kim wrote:

On Tue, Apr 10, 2018 at 09:37:53AM +0300, Oleksandr Andrushchenko
wrote:

On 04/06/2018 09:57 PM, Dongwon Kim wrote:

On Fri, Apr 06, 2018 at 03:36:03PM +0300, Oleksandr Andrushchenko
wrote:

On 04/06/2018 02:57 PM, Gerd Hoffmann wrote:

  Hi,


I fail to see any common ground for xen-zcopy and udmabuf ...

Does the above mean you can assume that xen-zcopy and udmabuf
can co-exist as two different solutions?

Well, udmabuf route isn't fully clear yet, but yes.

See also gvt (intel vgpu), where the hypervisor interface is
abstracted
away into a separate kernel modules even though most of the actual
vgpu
emulation code is common.

Thank you for your input, I'm just trying to figure out
which of the three z-copy solutions intersect and how much

And what about hyper-dmabuf?

xen z-copy solution is pretty similar fundamentally to hyper_dmabuf
in terms of these core sharing feature:

1. the sharing process - import prime/dmabuf from the producer ->
extract
underlying pages and get those shared -> return references for
shared pages

Another thing is danvet was kind of against to the idea of importing
existing
dmabuf/prime buffer and forward it to the other domain due to
synchronization
issues. He proposed to make hyper_dmabuf only work as an exporter so
that it
can have a full control over the buffer. I think we need to talk about
this
further as well.

Yes, I saw this. But this limits the use-cases so much.
For instance, running Android as a Guest (which uses ION to allocate
buffers) means that finally HW composer will import dma-buf into
the DRM driver. Then, in case of xen-front for example, it needs to be
shared with the backend (Host side). Of course, we can change
user-space
to make xen-front allocate the buffers (make it exporter), but what we
try
to avoid is to change user-space which in normal world would have
remain
unchanged otherwise.
So, I do think we have to support this use-case and just have to
understand
the complexity.

Erm, why do you need importer capability for this use-case?

guest1 -> ION -> xen-front -> hypervisor -> guest 2 -> xen-zcopy exposes
that dma-buf -> import to the real display hw

No where in this chain do you need xen-zcopy to be able to import a
dma-buf (within linux, it needs to import a bunch of pages from the
hypervisor).

Now if your plan is to use xen-zcopy in the guest1 instead of xen-front,
then you indeed need to import.

This is the exact use-case I was referring to while saying
we need to import on Guest1 side. If hyper-dmabuf is so
generic that there is no xen-front in the picture, then
it needs to import a dma-buf, so it can be exported at Guest2 side.

But that imo doesn't make sense:
- xen-front gives you clearly defined flip events you can forward to the
 hypervisor. xen-zcopy would need to add that again.

xen-zcopy is a helper driver which doesn't handle page flips
and is not a KMS driver as one might think of: the DRM UAPI it uses is
just to export a dma-buf as a PRIME buffer, but that's it.
Flipping etc. is done by the backend [1], not xen-zcopy.

Same for
 hyperdmabuf (and really we're not going to shuffle struct dma_fence
over
 the wire in a generic fashion between hypervisor guests).

- xen-front already has the idea of pixel format for the buffer (and any
 other metadata). Again, xen-zcopy and hyperdmabuf lack that, would
need
 to add it shoehorned in somehow.

Again, here you are talking of something which is implemented in
Xen display backend, not xen-zcopy, e.g. display backend can
implement para-virtual display w/o xen-zcopy at all, but in this case
there is a memory copying for each frame. With the help of xen-zcopy
the backend feeds xen-front's buffers directly into Guest2 DRM/KMS or
Weston or whatever as xen-zcopy exports remote buffers as PRIME buffers,
thus no buffer copying is required.

Why do you need to copy on every frame for xen-front? In the above
pipeline, using xen-front I see 0 architectural reasons to have a copy
anywhere.

This seems to be the core of the confusion we're having here.

Ok, so I'll try to explain:
1. xen-front - produces a display buffer to be shown at Guest2
by the backend, shares its grant references with the backend
2. xen-front sends page flip event to the backend specifying the
buffer in question
3. Backend takes the shared buffer (which is only a buffer mapped into
backend's memory, it is not a dma-buf/PRIME one) and makes memcpy from
it to a local dumb/surface

Why do you even do that? The copying here I mean - why don't you just
directly scan out from the grant 

Re: [RfC PATCH] Add udmabuf misc device

[Daniel Vetter]

On Mon, Apr 16, 2018 at 10:22 AM, Oleksandr Andrushchenko
 wrote:
> On 04/16/2018 10:43 AM, Daniel Vetter wrote:
>>
>> On Mon, Apr 16, 2018 at 10:16:31AM +0300, Oleksandr Andrushchenko wrote:
>>>
>>> On 04/13/2018 06:37 PM, Daniel Vetter wrote:

 On Wed, Apr 11, 2018 at 08:59:32AM +0300, Oleksandr Andrushchenko wrote:
>
> On 04/10/2018 08:26 PM, Dongwon Kim wrote:
>>
>> On Tue, Apr 10, 2018 at 09:37:53AM +0300, Oleksandr Andrushchenko
>> wrote:
>>>
>>> On 04/06/2018 09:57 PM, Dongwon Kim wrote:

 On Fri, Apr 06, 2018 at 03:36:03PM +0300, Oleksandr Andrushchenko
 wrote:
>
> On 04/06/2018 02:57 PM, Gerd Hoffmann wrote:
>>
>>  Hi,
>>
 I fail to see any common ground for xen-zcopy and udmabuf ...
>>>
>>> Does the above mean you can assume that xen-zcopy and udmabuf
>>> can co-exist as two different solutions?
>>
>> Well, udmabuf route isn't fully clear yet, but yes.
>>
>> See also gvt (intel vgpu), where the hypervisor interface is
>> abstracted
>> away into a separate kernel modules even though most of the actual
>> vgpu
>> emulation code is common.
>
> Thank you for your input, I'm just trying to figure out
> which of the three z-copy solutions intersect and how much
>>>
>>> And what about hyper-dmabuf?

 xen z-copy solution is pretty similar fundamentally to hyper_dmabuf
 in terms of these core sharing feature:

 1. the sharing process - import prime/dmabuf from the producer ->
 extract
 underlying pages and get those shared -> return references for
 shared pages
>>
>> Another thing is danvet was kind of against to the idea of importing
>> existing
>> dmabuf/prime buffer and forward it to the other domain due to
>> synchronization
>> issues. He proposed to make hyper_dmabuf only work as an exporter so
>> that it
>> can have a full control over the buffer. I think we need to talk about
>> this
>> further as well.
>
> Yes, I saw this. But this limits the use-cases so much.
> For instance, running Android as a Guest (which uses ION to allocate
> buffers) means that finally HW composer will import dma-buf into
> the DRM driver. Then, in case of xen-front for example, it needs to be
> shared with the backend (Host side). Of course, we can change
> user-space
> to make xen-front allocate the buffers (make it exporter), but what we
> try
> to avoid is to change user-space which in normal world would have
> remain
> unchanged otherwise.
> So, I do think we have to support this use-case and just have to
> understand
> the complexity.

 Erm, why do you need importer capability for this use-case?

 guest1 -> ION -> xen-front -> hypervisor -> guest 2 -> xen-zcopy exposes
 that dma-buf -> import to the real display hw

 No where in this chain do you need xen-zcopy to be able to import a
 dma-buf (within linux, it needs to import a bunch of pages from the
 hypervisor).

 Now if your plan is to use xen-zcopy in the guest1 instead of xen-front,
 then you indeed need to import.
>>>
>>> This is the exact use-case I was referring to while saying
>>> we need to import on Guest1 side. If hyper-dmabuf is so
>>> generic that there is no xen-front in the picture, then
>>> it needs to import a dma-buf, so it can be exported at Guest2 side.

But that imo doesn't make sense:
 - xen-front gives you clearly defined flip events you can forward to the
 hypervisor. xen-zcopy would need to add that again.
>>>
>>> xen-zcopy is a helper driver which doesn't handle page flips
>>> and is not a KMS driver as one might think of: the DRM UAPI it uses is
>>> just to export a dma-buf as a PRIME buffer, but that's it.
>>> Flipping etc. is done by the backend [1], not xen-zcopy.

Same for
 hyperdmabuf (and really we're not going to shuffle struct dma_fence
 over
 the wire in a generic fashion between hypervisor guests).

 - xen-front already has the idea of pixel format for the buffer (and any
 other metadata). Again, xen-zcopy and hyperdmabuf lack that, would
 need
 to add it shoehorned in somehow.
>>>
>>> Again, here you are talking of something which is implemented in
>>> Xen display backend, not xen-zcopy, e.g. display backend can
>>> implement para-virtual display w/o xen-zcopy at all, but in this case
>>> there is a memory copying for each frame. With the help of xen-zcopy
>>> the backend feeds xen-front's buffers directly into Guest2 DRM/KMS or
>>> Weston or whatever as xen-zcopy exports remote buffers as PRIME buffers,
>>> thus no buffer copying is required.
>>
>> Why do you need to copy on 

Re: [RfC PATCH] Add udmabuf misc device

[Oleksandr Andrushchenko]

On 04/16/2018 10:43 AM, Daniel Vetter wrote:

On Mon, Apr 16, 2018 at 10:16:31AM +0300, Oleksandr Andrushchenko wrote:

On 04/13/2018 06:37 PM, Daniel Vetter wrote:

On Wed, Apr 11, 2018 at 08:59:32AM +0300, Oleksandr Andrushchenko wrote:

On 04/10/2018 08:26 PM, Dongwon Kim wrote:

On Tue, Apr 10, 2018 at 09:37:53AM +0300, Oleksandr Andrushchenko wrote:

On 04/06/2018 09:57 PM, Dongwon Kim wrote:

On Fri, Apr 06, 2018 at 03:36:03PM +0300, Oleksandr Andrushchenko wrote:

On 04/06/2018 02:57 PM, Gerd Hoffmann wrote:

 Hi,


I fail to see any common ground for xen-zcopy and udmabuf ...

Does the above mean you can assume that xen-zcopy and udmabuf
can co-exist as two different solutions?

Well, udmabuf route isn't fully clear yet, but yes.

See also gvt (intel vgpu), where the hypervisor interface is abstracted
away into a separate kernel modules even though most of the actual vgpu
emulation code is common.

Thank you for your input, I'm just trying to figure out
which of the three z-copy solutions intersect and how much

And what about hyper-dmabuf?

xen z-copy solution is pretty similar fundamentally to hyper_dmabuf
in terms of these core sharing feature:

1. the sharing process - import prime/dmabuf from the producer -> extract
underlying pages and get those shared -> return references for shared pages

Another thing is danvet was kind of against to the idea of importing existing
dmabuf/prime buffer and forward it to the other domain due to synchronization
issues. He proposed to make hyper_dmabuf only work as an exporter so that it
can have a full control over the buffer. I think we need to talk about this
further as well.

Yes, I saw this. But this limits the use-cases so much.
For instance, running Android as a Guest (which uses ION to allocate
buffers) means that finally HW composer will import dma-buf into
the DRM driver. Then, in case of xen-front for example, it needs to be
shared with the backend (Host side). Of course, we can change user-space
to make xen-front allocate the buffers (make it exporter), but what we try
to avoid is to change user-space which in normal world would have remain
unchanged otherwise.
So, I do think we have to support this use-case and just have to understand
the complexity.

Erm, why do you need importer capability for this use-case?

guest1 -> ION -> xen-front -> hypervisor -> guest 2 -> xen-zcopy exposes
that dma-buf -> import to the real display hw

No where in this chain do you need xen-zcopy to be able to import a
dma-buf (within linux, it needs to import a bunch of pages from the
hypervisor).

Now if your plan is to use xen-zcopy in the guest1 instead of xen-front,
then you indeed need to import.

This is the exact use-case I was referring to while saying
we need to import on Guest1 side. If hyper-dmabuf is so
generic that there is no xen-front in the picture, then
it needs to import a dma-buf, so it can be exported at Guest2 side.

   But that imo doesn't make sense:
- xen-front gives you clearly defined flip events you can forward to the
hypervisor. xen-zcopy would need to add that again.

xen-zcopy is a helper driver which doesn't handle page flips
and is not a KMS driver as one might think of: the DRM UAPI it uses is
just to export a dma-buf as a PRIME buffer, but that's it.
Flipping etc. is done by the backend [1], not xen-zcopy.

   Same for
hyperdmabuf (and really we're not going to shuffle struct dma_fence over
the wire in a generic fashion between hypervisor guests).

- xen-front already has the idea of pixel format for the buffer (and any
other metadata). Again, xen-zcopy and hyperdmabuf lack that, would need
to add it shoehorned in somehow.

Again, here you are talking of something which is implemented in
Xen display backend, not xen-zcopy, e.g. display backend can
implement para-virtual display w/o xen-zcopy at all, but in this case
there is a memory copying for each frame. With the help of xen-zcopy
the backend feeds xen-front's buffers directly into Guest2 DRM/KMS or
Weston or whatever as xen-zcopy exports remote buffers as PRIME buffers,
thus no buffer copying is required.

Why do you need to copy on every frame for xen-front? In the above
pipeline, using xen-front I see 0 architectural reasons to have a copy
anywhere.

This seems to be the core of the confusion we're having here.

Ok, so I'll try to explain:
1. xen-front - produces a display buffer to be shown at Guest2
by the backend, shares its grant references with the backend
2. xen-front sends page flip event to the backend specifying the
buffer in question
3. Backend takes the shared buffer (which is only a buffer mapped into
backend's memory, it is not a dma-buf/PRIME one) and makes memcpy from
it to a local dumb/surface
4. Backend flips that local dumb buffer/surface

If I have a xen-zcopy helper driver then I can avoid doing step 3):
1) 2) remain the same as above
3) Initially for a new display buffer, backend calls xen-zcopy to create
a local PRIME buffer from the 

Re: [RfC PATCH] Add udmabuf misc device

[Daniel Vetter]

On Mon, Apr 16, 2018 at 10:16:31AM +0300, Oleksandr Andrushchenko wrote:
> On 04/13/2018 06:37 PM, Daniel Vetter wrote:
> > On Wed, Apr 11, 2018 at 08:59:32AM +0300, Oleksandr Andrushchenko wrote:
> > > On 04/10/2018 08:26 PM, Dongwon Kim wrote:
> > > > On Tue, Apr 10, 2018 at 09:37:53AM +0300, Oleksandr Andrushchenko wrote:
> > > > > On 04/06/2018 09:57 PM, Dongwon Kim wrote:
> > > > > > On Fri, Apr 06, 2018 at 03:36:03PM +0300, Oleksandr Andrushchenko 
> > > > > > wrote:
> > > > > > > On 04/06/2018 02:57 PM, Gerd Hoffmann wrote:
> > > > > > > > Hi,
> > > > > > > > 
> > > > > > > > > > I fail to see any common ground for xen-zcopy and udmabuf 
> > > > > > > > > > ...
> > > > > > > > > Does the above mean you can assume that xen-zcopy and udmabuf
> > > > > > > > > can co-exist as two different solutions?
> > > > > > > > Well, udmabuf route isn't fully clear yet, but yes.
> > > > > > > > 
> > > > > > > > See also gvt (intel vgpu), where the hypervisor interface is 
> > > > > > > > abstracted
> > > > > > > > away into a separate kernel modules even though most of the 
> > > > > > > > actual vgpu
> > > > > > > > emulation code is common.
> > > > > > > Thank you for your input, I'm just trying to figure out
> > > > > > > which of the three z-copy solutions intersect and how much
> > > > > > > > > And what about hyper-dmabuf?
> > > > > > xen z-copy solution is pretty similar fundamentally to hyper_dmabuf
> > > > > > in terms of these core sharing feature:
> > > > > > 
> > > > > > 1. the sharing process - import prime/dmabuf from the producer -> 
> > > > > > extract
> > > > > > underlying pages and get those shared -> return references for 
> > > > > > shared pages
> > > > Another thing is danvet was kind of against to the idea of importing 
> > > > existing
> > > > dmabuf/prime buffer and forward it to the other domain due to 
> > > > synchronization
> > > > issues. He proposed to make hyper_dmabuf only work as an exporter so 
> > > > that it
> > > > can have a full control over the buffer. I think we need to talk about 
> > > > this
> > > > further as well.
> > > Yes, I saw this. But this limits the use-cases so much.
> > > For instance, running Android as a Guest (which uses ION to allocate
> > > buffers) means that finally HW composer will import dma-buf into
> > > the DRM driver. Then, in case of xen-front for example, it needs to be
> > > shared with the backend (Host side). Of course, we can change user-space
> > > to make xen-front allocate the buffers (make it exporter), but what we try
> > > to avoid is to change user-space which in normal world would have remain
> > > unchanged otherwise.
> > > So, I do think we have to support this use-case and just have to 
> > > understand
> > > the complexity.
> > Erm, why do you need importer capability for this use-case?
> > 
> > guest1 -> ION -> xen-front -> hypervisor -> guest 2 -> xen-zcopy exposes
> > that dma-buf -> import to the real display hw
> > 
> > No where in this chain do you need xen-zcopy to be able to import a
> > dma-buf (within linux, it needs to import a bunch of pages from the
> > hypervisor).
> > 
> > Now if your plan is to use xen-zcopy in the guest1 instead of xen-front,
> > then you indeed need to import.
> This is the exact use-case I was referring to while saying
> we need to import on Guest1 side. If hyper-dmabuf is so
> generic that there is no xen-front in the picture, then
> it needs to import a dma-buf, so it can be exported at Guest2 side.
> >   But that imo doesn't make sense:
> > - xen-front gives you clearly defined flip events you can forward to the
> >hypervisor. xen-zcopy would need to add that again.
> xen-zcopy is a helper driver which doesn't handle page flips
> and is not a KMS driver as one might think of: the DRM UAPI it uses is
> just to export a dma-buf as a PRIME buffer, but that's it.
> Flipping etc. is done by the backend [1], not xen-zcopy.
> >   Same for
> >hyperdmabuf (and really we're not going to shuffle struct dma_fence over
> >the wire in a generic fashion between hypervisor guests).
> > 
> > - xen-front already has the idea of pixel format for the buffer (and any
> >other metadata). Again, xen-zcopy and hyperdmabuf lack that, would need
> >to add it shoehorned in somehow.
> Again, here you are talking of something which is implemented in
> Xen display backend, not xen-zcopy, e.g. display backend can
> implement para-virtual display w/o xen-zcopy at all, but in this case
> there is a memory copying for each frame. With the help of xen-zcopy
> the backend feeds xen-front's buffers directly into Guest2 DRM/KMS or
> Weston or whatever as xen-zcopy exports remote buffers as PRIME buffers,
> thus no buffer copying is required.

Why do you need to copy on every frame for xen-front? In the above
pipeline, using xen-front I see 0 architectural reasons to have a copy
anywhere.

This seems to be the core of the confusion we're having here.

> > Ofc you won't be able to shovel sound or media 

Re: [RfC PATCH] Add udmabuf misc device

[Oleksandr Andrushchenko]

On 04/13/2018 06:37 PM, Daniel Vetter wrote:

On Wed, Apr 11, 2018 at 08:59:32AM +0300, Oleksandr Andrushchenko wrote:

On 04/10/2018 08:26 PM, Dongwon Kim wrote:

On Tue, Apr 10, 2018 at 09:37:53AM +0300, Oleksandr Andrushchenko wrote:

On 04/06/2018 09:57 PM, Dongwon Kim wrote:

On Fri, Apr 06, 2018 at 03:36:03PM +0300, Oleksandr Andrushchenko wrote:

On 04/06/2018 02:57 PM, Gerd Hoffmann wrote:

Hi,


I fail to see any common ground for xen-zcopy and udmabuf ...

Does the above mean you can assume that xen-zcopy and udmabuf
can co-exist as two different solutions?

Well, udmabuf route isn't fully clear yet, but yes.

See also gvt (intel vgpu), where the hypervisor interface is abstracted
away into a separate kernel modules even though most of the actual vgpu
emulation code is common.

Thank you for your input, I'm just trying to figure out
which of the three z-copy solutions intersect and how much

And what about hyper-dmabuf?

xen z-copy solution is pretty similar fundamentally to hyper_dmabuf
in terms of these core sharing feature:

1. the sharing process - import prime/dmabuf from the producer -> extract
underlying pages and get those shared -> return references for shared pages

Another thing is danvet was kind of against to the idea of importing existing
dmabuf/prime buffer and forward it to the other domain due to synchronization
issues. He proposed to make hyper_dmabuf only work as an exporter so that it
can have a full control over the buffer. I think we need to talk about this
further as well.

Yes, I saw this. But this limits the use-cases so much.
For instance, running Android as a Guest (which uses ION to allocate
buffers) means that finally HW composer will import dma-buf into
the DRM driver. Then, in case of xen-front for example, it needs to be
shared with the backend (Host side). Of course, we can change user-space
to make xen-front allocate the buffers (make it exporter), but what we try
to avoid is to change user-space which in normal world would have remain
unchanged otherwise.
So, I do think we have to support this use-case and just have to understand
the complexity.

Erm, why do you need importer capability for this use-case?

guest1 -> ION -> xen-front -> hypervisor -> guest 2 -> xen-zcopy exposes
that dma-buf -> import to the real display hw

No where in this chain do you need xen-zcopy to be able to import a
dma-buf (within linux, it needs to import a bunch of pages from the
hypervisor).

Now if your plan is to use xen-zcopy in the guest1 instead of xen-front,
then you indeed need to import.

This is the exact use-case I was referring to while saying
we need to import on Guest1 side. If hyper-dmabuf is so
generic that there is no xen-front in the picture, then
it needs to import a dma-buf, so it can be exported at Guest2 side.

  But that imo doesn't make sense:
- xen-front gives you clearly defined flip events you can forward to the
   hypervisor. xen-zcopy would need to add that again.

xen-zcopy is a helper driver which doesn't handle page flips
and is not a KMS driver as one might think of: the DRM UAPI it uses is
just to export a dma-buf as a PRIME buffer, but that's it.
Flipping etc. is done by the backend [1], not xen-zcopy.

  Same for
   hyperdmabuf (and really we're not going to shuffle struct dma_fence over
   the wire in a generic fashion between hypervisor guests).

- xen-front already has the idea of pixel format for the buffer (and any
   other metadata). Again, xen-zcopy and hyperdmabuf lack that, would need
   to add it shoehorned in somehow.

Again, here you are talking of something which is implemented in
Xen display backend, not xen-zcopy, e.g. display backend can
implement para-virtual display w/o xen-zcopy at all, but in this case
there is a memory copying for each frame. With the help of xen-zcopy
the backend feeds xen-front's buffers directly into Guest2 DRM/KMS or
Weston or whatever as xen-zcopy exports remote buffers as PRIME buffers,
thus no buffer copying is required.


Ofc you won't be able to shovel sound or media stream data over to another
guest like this, but that's what you have xen-v4l and xen-sound or
whatever else for. Trying to make a new uapi, which means userspace must
be changed for all the different use-case, instead of reusing standard
linux driver uapi (which just happens to send the data to another
hypervisor guest instead of real hw) imo just doesn't make much sense.

Also, at least for the gpu subsystem: Any new uapi must have full
userspace available for it, see:

https://dri.freedesktop.org/docs/drm/gpu/drm-uapi.html#open-source-userspace-requirements

Adding more uapi is definitely the most painful way to fix a use-case.
Personally I'd go as far and also change the xen-zcopy side on the
receiving guest to use some standard linux uapi. E.g. you could write an
output v4l driver to receive the frames from guest1.

So, we now know that xen-zcopy was not meant to handle page flips,
but to implement new UAPI to let user-space 

Re: [RfC PATCH] Add udmabuf misc device

[Daniel Vetter]

On Wed, Apr 11, 2018 at 08:59:32AM +0300, Oleksandr Andrushchenko wrote:
> On 04/10/2018 08:26 PM, Dongwon Kim wrote:
> > On Tue, Apr 10, 2018 at 09:37:53AM +0300, Oleksandr Andrushchenko wrote:
> > > On 04/06/2018 09:57 PM, Dongwon Kim wrote:
> > > > On Fri, Apr 06, 2018 at 03:36:03PM +0300, Oleksandr Andrushchenko wrote:
> > > > > On 04/06/2018 02:57 PM, Gerd Hoffmann wrote:
> > > > > >Hi,
> > > > > > 
> > > > > > > > I fail to see any common ground for xen-zcopy and udmabuf ...
> > > > > > > Does the above mean you can assume that xen-zcopy and udmabuf
> > > > > > > can co-exist as two different solutions?
> > > > > > Well, udmabuf route isn't fully clear yet, but yes.
> > > > > > 
> > > > > > See also gvt (intel vgpu), where the hypervisor interface is 
> > > > > > abstracted
> > > > > > away into a separate kernel modules even though most of the actual 
> > > > > > vgpu
> > > > > > emulation code is common.
> > > > > Thank you for your input, I'm just trying to figure out
> > > > > which of the three z-copy solutions intersect and how much
> > > > > > > And what about hyper-dmabuf?
> > > > xen z-copy solution is pretty similar fundamentally to hyper_dmabuf
> > > > in terms of these core sharing feature:
> > > > 
> > > > 1. the sharing process - import prime/dmabuf from the producer -> 
> > > > extract
> > > > underlying pages and get those shared -> return references for shared 
> > > > pages
> > Another thing is danvet was kind of against to the idea of importing 
> > existing
> > dmabuf/prime buffer and forward it to the other domain due to 
> > synchronization
> > issues. He proposed to make hyper_dmabuf only work as an exporter so that it
> > can have a full control over the buffer. I think we need to talk about this
> > further as well.
> Yes, I saw this. But this limits the use-cases so much.
> For instance, running Android as a Guest (which uses ION to allocate
> buffers) means that finally HW composer will import dma-buf into
> the DRM driver. Then, in case of xen-front for example, it needs to be
> shared with the backend (Host side). Of course, we can change user-space
> to make xen-front allocate the buffers (make it exporter), but what we try
> to avoid is to change user-space which in normal world would have remain
> unchanged otherwise.
> So, I do think we have to support this use-case and just have to understand
> the complexity.

Erm, why do you need importer capability for this use-case?

guest1 -> ION -> xen-front -> hypervisor -> guest 2 -> xen-zcopy exposes
that dma-buf -> import to the real display hw

No where in this chain do you need xen-zcopy to be able to import a
dma-buf (within linux, it needs to import a bunch of pages from the
hypervisor).

Now if your plan is to use xen-zcopy in the guest1 instead of xen-front,
then you indeed need to import. But that imo doesn't make sense:
- xen-front gives you clearly defined flip events you can forward to the
  hypervisor. xen-zcopy would need to add that again. Same for
  hyperdmabuf (and really we're not going to shuffle struct dma_fence over
  the wire in a generic fashion between hypervisor guests).

- xen-front already has the idea of pixel format for the buffer (and any
  other metadata). Again, xen-zcopy and hyperdmabuf lack that, would need
  to add it shoehorned in somehow.

Ofc you won't be able to shovel sound or media stream data over to another
guest like this, but that's what you have xen-v4l and xen-sound or
whatever else for. Trying to make a new uapi, which means userspace must
be changed for all the different use-case, instead of reusing standard
linux driver uapi (which just happens to send the data to another
hypervisor guest instead of real hw) imo just doesn't make much sense.

Also, at least for the gpu subsystem: Any new uapi must have full
userspace available for it, see:

https://dri.freedesktop.org/docs/drm/gpu/drm-uapi.html#open-source-userspace-requirements

Adding more uapi is definitely the most painful way to fix a use-case.
Personally I'd go as far and also change the xen-zcopy side on the
receiving guest to use some standard linux uapi. E.g. you could write an
output v4l driver to receive the frames from guest1.

> > danvet, can you comment on this topic?
> > 
> > > > 2. the page sharing mechanism - it uses Xen-grant-table.
> > > > 
> > > > And to give you a quick summary of differences as far as I understand
> > > > between two implementations (please correct me if I am wrong, 
> > > > Oleksandr.)
> > > > 
> > > > 1. xen-zcopy is DRM specific - can import only DRM prime buffer
> > > > while hyper_dmabuf can export any dmabuf regardless of originator
> > > Well, this is true. And at the same time this is just a matter
> > > of extending the API: xen-zcopy is a helper driver designed for
> > > xen-front/back use-case, so this is why it only has DRM PRIME API
> > > > 2. xen-zcopy doesn't seem to have dma-buf synchronization between two 
> > > > VMs
> > > > while (as danvet called it as remote 

Re: [RfC PATCH] Add udmabuf misc device

[Oleksandr Andrushchenko]

On 04/10/2018 08:26 PM, Dongwon Kim wrote:

On Tue, Apr 10, 2018 at 09:37:53AM +0300, Oleksandr Andrushchenko wrote:

On 04/06/2018 09:57 PM, Dongwon Kim wrote:

On Fri, Apr 06, 2018 at 03:36:03PM +0300, Oleksandr Andrushchenko wrote:

On 04/06/2018 02:57 PM, Gerd Hoffmann wrote:

   Hi,


I fail to see any common ground for xen-zcopy and udmabuf ...

Does the above mean you can assume that xen-zcopy and udmabuf
can co-exist as two different solutions?

Well, udmabuf route isn't fully clear yet, but yes.

See also gvt (intel vgpu), where the hypervisor interface is abstracted
away into a separate kernel modules even though most of the actual vgpu
emulation code is common.

Thank you for your input, I'm just trying to figure out
which of the three z-copy solutions intersect and how much

And what about hyper-dmabuf?

xen z-copy solution is pretty similar fundamentally to hyper_dmabuf
in terms of these core sharing feature:

1. the sharing process - import prime/dmabuf from the producer -> extract
underlying pages and get those shared -> return references for shared pages

Another thing is danvet was kind of against to the idea of importing existing
dmabuf/prime buffer and forward it to the other domain due to synchronization
issues. He proposed to make hyper_dmabuf only work as an exporter so that it
can have a full control over the buffer. I think we need to talk about this
further as well.

Yes, I saw this. But this limits the use-cases so much.
For instance, running Android as a Guest (which uses ION to allocate
buffers) means that finally HW composer will import dma-buf into
the DRM driver. Then, in case of xen-front for example, it needs to be
shared with the backend (Host side). Of course, we can change user-space
to make xen-front allocate the buffers (make it exporter), but what we try
to avoid is to change user-space which in normal world would have remain
unchanged otherwise.
So, I do think we have to support this use-case and just have to understand
the complexity.



danvet, can you comment on this topic?


2. the page sharing mechanism - it uses Xen-grant-table.

And to give you a quick summary of differences as far as I understand
between two implementations (please correct me if I am wrong, Oleksandr.)

1. xen-zcopy is DRM specific - can import only DRM prime buffer
while hyper_dmabuf can export any dmabuf regardless of originator

Well, this is true. And at the same time this is just a matter
of extending the API: xen-zcopy is a helper driver designed for
xen-front/back use-case, so this is why it only has DRM PRIME API

2. xen-zcopy doesn't seem to have dma-buf synchronization between two VMs
while (as danvet called it as remote dmabuf api sharing) hyper_dmabuf sends
out synchronization message to the exporting VM for synchronization.

This is true. Again, this is because of the use-cases it covers.
But having synchronization for a generic solution seems to be a good idea.

Yeah, understood xen-zcopy works ok with your use case. But I am just curious
if it is ok not to have any inter-domain synchronization in this sharing model.

The synchronization is done with displif protocol [1]

The buffer being shared is technically dma-buf and originator needs to be able
to keep track of it.

As I am working in DRM terms the tracking is done by the DRM core
for me for free. (This might be one of the reasons Daniel sees DRM
based implementation fit very good from code-reuse POV).



3. 1-level references - when using grant-table for sharing pages, there will
be same # of refs (each 8 byte)

To be precise, grant ref is 4 bytes

You are right. Thanks for correction.;)


as # of shared pages, which is passed to
the userspace to be shared with importing VM in case of xen-zcopy.

The reason for that is that xen-zcopy is a helper driver, e.g.
the grant references come from the display backend [1], which implements
Xen display protocol [2]. So, effectively the backend extracts references
from frontend's requests and passes those to xen-zcopy as an array
of refs.

  Compared
to this, hyper_dmabuf does multiple level addressing to generate only one
reference id that represents all shared pages.

In the protocol [2] only one reference to the gref directory is passed
between VMs
(and the gref directory is a single-linked list of shared pages containing
all
of the grefs of the buffer).

ok, good to know. I will look into its implementation in more details but is
this gref directory (chained grefs) something that can be used for any general
memory sharing use case or is it jsut for xen-display (in current code base)?

Not to mislead you: one grant ref is passed via displif protocol,
but the page it's referencing contains the rest of the grant refs.

As to if this can be used for any memory: yes. It is the same for
sndif and displif Xen protocols, but defined twice as strictly speaking
sndif and displif are two separate protocols.

While reviewing your RFC v2 one of the comments I had [2] was that if we
can start 

Re: [RfC PATCH] Add udmabuf misc device

[Dongwon Kim]

On Tue, Apr 10, 2018 at 09:37:53AM +0300, Oleksandr Andrushchenko wrote:
> On 04/06/2018 09:57 PM, Dongwon Kim wrote:
> >On Fri, Apr 06, 2018 at 03:36:03PM +0300, Oleksandr Andrushchenko wrote:
> >>On 04/06/2018 02:57 PM, Gerd Hoffmann wrote:
> >>>   Hi,
> >>>
> >I fail to see any common ground for xen-zcopy and udmabuf ...
> Does the above mean you can assume that xen-zcopy and udmabuf
> can co-exist as two different solutions?
> >>>Well, udmabuf route isn't fully clear yet, but yes.
> >>>
> >>>See also gvt (intel vgpu), where the hypervisor interface is abstracted
> >>>away into a separate kernel modules even though most of the actual vgpu
> >>>emulation code is common.
> >>Thank you for your input, I'm just trying to figure out
> >>which of the three z-copy solutions intersect and how much
> And what about hyper-dmabuf?
> >xen z-copy solution is pretty similar fundamentally to hyper_dmabuf
> >in terms of these core sharing feature:
> >
> >1. the sharing process - import prime/dmabuf from the producer -> extract
> >underlying pages and get those shared -> return references for shared pages

Another thing is danvet was kind of against to the idea of importing existing
dmabuf/prime buffer and forward it to the other domain due to synchronization
issues. He proposed to make hyper_dmabuf only work as an exporter so that it
can have a full control over the buffer. I think we need to talk about this
further as well.

danvet, can you comment on this topic?

> >
> >2. the page sharing mechanism - it uses Xen-grant-table.
> >
> >And to give you a quick summary of differences as far as I understand
> >between two implementations (please correct me if I am wrong, Oleksandr.)
> >
> >1. xen-zcopy is DRM specific - can import only DRM prime buffer
> >while hyper_dmabuf can export any dmabuf regardless of originator
> Well, this is true. And at the same time this is just a matter
> of extending the API: xen-zcopy is a helper driver designed for
> xen-front/back use-case, so this is why it only has DRM PRIME API
> >
> >2. xen-zcopy doesn't seem to have dma-buf synchronization between two VMs
> >while (as danvet called it as remote dmabuf api sharing) hyper_dmabuf sends
> >out synchronization message to the exporting VM for synchronization.
> This is true. Again, this is because of the use-cases it covers.
> But having synchronization for a generic solution seems to be a good idea.

Yeah, understood xen-zcopy works ok with your use case. But I am just curious
if it is ok not to have any inter-domain synchronization in this sharing model.
The buffer being shared is technically dma-buf and originator needs to be able
to keep track of it.

> >
> >3. 1-level references - when using grant-table for sharing pages, there will
> >be same # of refs (each 8 byte)
> To be precise, grant ref is 4 bytes
You are right. Thanks for correction.;)

> >as # of shared pages, which is passed to
> >the userspace to be shared with importing VM in case of xen-zcopy.
> The reason for that is that xen-zcopy is a helper driver, e.g.
> the grant references come from the display backend [1], which implements
> Xen display protocol [2]. So, effectively the backend extracts references
> from frontend's requests and passes those to xen-zcopy as an array
> of refs.
> >  Compared
> >to this, hyper_dmabuf does multiple level addressing to generate only one
> >reference id that represents all shared pages.
> In the protocol [2] only one reference to the gref directory is passed
> between VMs
> (and the gref directory is a single-linked list of shared pages containing
> all
> of the grefs of the buffer).

ok, good to know. I will look into its implementation in more details but is
this gref directory (chained grefs) something that can be used for any general
memory sharing use case or is it jsut for xen-display (in current code base)?

> 
> >
> >4. inter VM messaging (hype_dmabuf only) - hyper_dmabuf has inter-vm msg
> >communication defined for dmabuf synchronization and private data (meta
> >info that Matt Roper mentioned) exchange.
> This is true, xen-zcopy has no means for inter VM sync and meta-data,
> simply because it doesn't have any code for inter VM exchange in it,
> e.g. the inter VM protocol is handled by the backend [1].
> >
> >5. driver-to-driver notification (hyper_dmabuf only) - importing VM gets
> >notified when newdmabuf is exported from other VM - uevent can be optionally
> >generated when this happens.
> >
> >6. structure - hyper_dmabuf is targetting to provide a generic solution for
> >inter-domain dmabuf sharing for most hypervisors, which is why it has two
> >layers as mattrope mentioned, front-end that contains standard API and 
> >backend
> >that is specific to hypervisor.
> Again, xen-zcopy is decoupled from inter VM communication
> >>>No idea, didn't look at it in detail.
> >>>
> >>>Looks pretty complex from a distant view.  Maybe because it tries to
> >>>build a communication framework using dma-bufs instead of a 

Re: [RfC PATCH] Add udmabuf misc device

[Gerd Hoffmann]

  Hi,

> Generally we try to cache mappings as much as possible. And wrt finding a
> slot: Create a sufficiently sized BAR on the virgl device, just for that?

Well.  virtio has no concept of "bars" ...

The most common virtio transport layer happens to be pci, which actually
has bars.  But we also have virtio-mmio (largely unused since arm got
pci) and virtio-ccw (used on s390x).

In any case it would be a layering violation.

Figured meanwhile qemu got memfd support recently, i.e. it can be
configured to back guest memory with memfd.  Which makes the memfd route
quite attractive.  Guess I try switch udmabuf to require memfd storage
as proof-of-concept.

cheers,
  Gerd

Re: [RfC PATCH] Add udmabuf misc device

[Oleksandr Andrushchenko]

On 04/06/2018 09:57 PM, Dongwon Kim wrote:

On Fri, Apr 06, 2018 at 03:36:03PM +0300, Oleksandr Andrushchenko wrote:

On 04/06/2018 02:57 PM, Gerd Hoffmann wrote:

   Hi,


I fail to see any common ground for xen-zcopy and udmabuf ...

Does the above mean you can assume that xen-zcopy and udmabuf
can co-exist as two different solutions?

Well, udmabuf route isn't fully clear yet, but yes.

See also gvt (intel vgpu), where the hypervisor interface is abstracted
away into a separate kernel modules even though most of the actual vgpu
emulation code is common.

Thank you for your input, I'm just trying to figure out
which of the three z-copy solutions intersect and how much

And what about hyper-dmabuf?

xen z-copy solution is pretty similar fundamentally to hyper_dmabuf
in terms of these core sharing feature:

1. the sharing process - import prime/dmabuf from the producer -> extract
underlying pages and get those shared -> return references for shared pages

2. the page sharing mechanism - it uses Xen-grant-table.

And to give you a quick summary of differences as far as I understand
between two implementations (please correct me if I am wrong, Oleksandr.)

1. xen-zcopy is DRM specific - can import only DRM prime buffer
while hyper_dmabuf can export any dmabuf regardless of originator

Well, this is true. And at the same time this is just a matter
of extending the API: xen-zcopy is a helper driver designed for
xen-front/back use-case, so this is why it only has DRM PRIME API


2. xen-zcopy doesn't seem to have dma-buf synchronization between two VMs
while (as danvet called it as remote dmabuf api sharing) hyper_dmabuf sends
out synchronization message to the exporting VM for synchronization.

This is true. Again, this is because of the use-cases it covers.
But having synchronization for a generic solution seems to be a good idea.


3. 1-level references - when using grant-table for sharing pages, there will
be same # of refs (each 8 byte)

To be precise, grant ref is 4 bytes

as # of shared pages, which is passed to
the userspace to be shared with importing VM in case of xen-zcopy.

The reason for that is that xen-zcopy is a helper driver, e.g.
the grant references come from the display backend [1], which implements
Xen display protocol [2]. So, effectively the backend extracts references
from frontend's requests and passes those to xen-zcopy as an array
of refs.

  Compared
to this, hyper_dmabuf does multiple level addressing to generate only one
reference id that represents all shared pages.
In the protocol [2] only one reference to the gref directory is passed 
between VMs
(and the gref directory is a single-linked list of shared pages 
containing all

of the grefs of the buffer).



4. inter VM messaging (hype_dmabuf only) - hyper_dmabuf has inter-vm msg
communication defined for dmabuf synchronization and private data (meta
info that Matt Roper mentioned) exchange.

This is true, xen-zcopy has no means for inter VM sync and meta-data,
simply because it doesn't have any code for inter VM exchange in it,
e.g. the inter VM protocol is handled by the backend [1].


5. driver-to-driver notification (hyper_dmabuf only) - importing VM gets
notified when newdmabuf is exported from other VM - uevent can be optionally
generated when this happens.

6. structure - hyper_dmabuf is targetting to provide a generic solution for
inter-domain dmabuf sharing for most hypervisors, which is why it has two
layers as mattrope mentioned, front-end that contains standard API and backend
that is specific to hypervisor.

Again, xen-zcopy is decoupled from inter VM communication

No idea, didn't look at it in detail.

Looks pretty complex from a distant view.  Maybe because it tries to
build a communication framework using dma-bufs instead of a simple
dma-buf passing mechanism.

we started with simple dma-buf sharing but realized there are many
things we need to consider in real use-case, so we added communication
, notification and dma-buf synchronization then re-structured it to
front-end and back-end (this made things more compicated..) since Xen
was not our only target. Also, we thought passing the reference for the
buffer (hyper_dmabuf_id) is not secure so added uvent mechanism later.


Yes, I am looking at it now, trying to figure out the full story
and its implementation. BTW, Intel guys were about to share some
test application for hyper-dmabuf, maybe I have missed one.
It could probably better explain the use-cases and the complexity
they have in hyper-dmabuf.

One example is actually in github. If you want take a look at it, please
visit:

https://github.com/downor/linux_hyper_dmabuf_test/tree/xen/simple_export

Thank you, I'll have a look

Like xen-zcopy it seems to depend on the idea that the hypervisor
manages all memory it is easy for guests to share pages with the help of
the hypervisor.

So, for xen-zcopy we were not trying to make it generic,
it just solves display (dumb) zero-copying use-cases for Xen.
We 

Re: [RfC PATCH] Add udmabuf misc device

[Daniel Vetter]

On Thu, Apr 05, 2018 at 05:11:17PM -0700, Matt Roper wrote:
> On Thu, Apr 05, 2018 at 10:32:04PM +0200, Daniel Vetter wrote:
> > Pulling this out of the shadows again.
> > 
> > We now also have xen-zcopy from Oleksandr and the hyper dmabuf stuff
> > from Matt and Dongwong.
> > 
> > At least from the intel side there seems to be the idea to just have 1
> > special device that can handle cross-gues/host sharing for all kinds
> > of hypervisors, so I guess you all need to work together :-)
> > 
> > Or we throw out the idea that hyper dmabuf will be cross-hypervisor
> > (not sure how useful/reasonable that is, someone please convince me
> > one way or the other).
> > 
> > Cheers, Daniel
> 
> Dongwon (DW) is the one doing all the real work on hyper_dmabuf, but I'm
> familiar with the use cases he's trying to address, and I think there
> are a couple high-level goals of his work that are worth calling out as
> we discuss the various options for sharing buffers produced in one VM
> with a consumer running in another VM:
> 
>  * We should try to keep the interface/usage separate from the
>underlying hypervisor implementation details.  I.e., in DW's design
>the sink/source drivers that handle the actual buffer passing in the
>two VM's should provide a generic interface that does not depend on a
>specific hypervisor.  Behind the scenes there could be various
>implementations for specific hypervisors (Xen, KVM, ACRN, etc.), and
>some of those backends may have additional restrictions, but it would
>be best if userspace didn't have to know the specific hypervisor
>running on the system and could just query the general capabilities
>available to it.  We've already got projects in flight that are
>wanting this functionality on Xen and ACRN today.

Two comments on this:

- Just because it's in drivers/gpu doesn't mean you can't use it for
  anything else. E.g. the xen-zcopy driver can very much be used for any
  dma-buf, there's nothing gpu specific with it - well besides that it
  resuses some useful DRM ioctls, but if that annoys you just do a #define
  TOTALLY_GENERIC DRM and be done :-)

- Especially the kvm memory and hypervisor model seems totally different
  from other hypervisors, e.g. no real use for guest-guest sharing (which
  doesn't go through the host) and other cases. So trying to make
  something 100% generic seems like a bad idea.

  Wrt making it generic: Just use generic interfaces - if you can somehow
  use xen-front for the display sharing, then a) no need for hyper-dmabuf
  and b) already fully generic since it looks like a normal drm device to
  the guest userspace.

>  * The general interface should be able to express sharing from any
>guest:guest, not just guest:host.  Arbitrary G:G sharing might be
>something some hypervisors simply aren't able to support, but the
>userspace API itself shouldn't make assumptions or restrict that.  I
>think ideally the sharing API would include some kind of
>query_targets interface that would return a list of VM's that your
>current OS is allowed to share with; that list would be depend on the
>policy established by the system integrator, but obviously wouldn't
>include targets that the hypervisor itself wouldn't be capable of
>handling.

Uh ... has a proper security architect analyzed this idea?

>  * A lot of the initial use cases are in the realm of graphics, but this
>shouldn't be a graphics-specific API.  Buffers might contain other
>types of content as well (e.g., audio).  Really the content producer
>could potentially be any driver (or userspace) running in the VM that
>knows how to import/export dma_buf's (or maybe just import given
>danvet's suggestion that we should make the sink driver do all the
>actual memory allocation for any buffers that may be shared).

See above, just because it uses drm ioctls doesn't make it gfx specific.

Otoh making it even more graphics specific might be even better, i.e. just
sharing the backend tech (grant tables or whatever), but having dedicated
front-ents for each use-case so there's less code to type.

>  * We need to be able to handle cross-VM coordination of buffer usage as
>well, so I think we'd want to include fence forwarding support in the
>API as well to signal back and forth about production/consumption
>completion.  And of course document really well what should happen
>if, for example, the entire VM you're sharing with/from dies.

Implicit fencing has been proven to be a bad idea. Please do explicit
passing of dma_fences (plus assorted protocol).

>  * The sharing API could be used to share multiple kinds of content in a
>single system.  The sharing sink driver running in the content
>producer's VM should accept some additional metadata that will be
>passed over to the target VM as well.  The sharing source driver
>running in the content consumer's VM would then be able to use 

Re: [RfC PATCH] Add udmabuf misc device

[Daniel Vetter]

On Fri, Apr 06, 2018 at 12:54:22PM +0200, Gerd Hoffmann wrote:
> On Fri, Apr 06, 2018 at 10:52:21AM +0100, Daniel Stone wrote:
> > Hi Gerd,
> > 
> > On 14 March 2018 at 08:03, Gerd Hoffmann  wrote:
> > >> Either mlock account (because it's mlocked defacto), and get_user_pages
> > >> won't do that for you.
> > >>
> > >> Or you write the full-blown userptr implementation, including 
> > >> mmu_notifier
> > >> support (see i915 or amdgpu), but that also requires Christian Königs
> > >> latest ->invalidate_mapping RFC for dma-buf (since atm exporting userptr
> > >> buffers is a no-go).
> > >
> > > I guess I'll look at mlock accounting for starters then.  Easier for
> > > now, and leaves the door open to switch to userptr later as this should
> > > be transparent to userspace.
> > 
> > Out of interest, do you have usecases for full userptr support? Maybe
> > another way would be to allow creation of dmabufs from memfds.
> 
> I have two things in mind.
> 
> One is vga emulation.  I have virtual pci memory bar for the virtual
> vga.  qemu backs vga memory with anonymous pages right now, switching
> that to shmem should be easy though if that makes things easier.  Guest
> places the framebuffer somewhere in the pci bar, and I want export the
> chunk which represents the framebuffer as dma-buf to display it on the
> host without copying around data.  Framebuffer is linear in guest
> physical memory, so a single block only.  That is the simpler case.
> 
> The more difficuilt one is virtio-gpu ressources.  virtio-gpu resources
> live in host memory (guest has no direct access).  The guest can
> optionally specify guest memory pages as backing storage for the
> resource.  Guest backing storage is allowed to be scattered.  Commands
> exist to copy both ways between host storage and guest backing.
> 
> With virgl (opengl acceleration) enabled the guest will send rendering
> commands to fill the framebuffer ressource, so there is no need to copy
> content to the framebuffer ressource.  The guest may fill other
> resources such as textures used for rendering with copy commands.
> 
> Without acceleration the guest does software-rendering to the backing
> storage, then sends a command to copy the framebuffer content from guest
> backing storage to host ressource.
> 
> Now it would be useful to allow a shared mapping, so no copying between
> guest backing storage and host resource is needed, especially for the
> software rendering case (i.e. dumb gem buffers).  Being able to export
> guest dumb buffers to other host processes would be useful too, for
> example to display guest windows seamlessly on the host wayland server.
> 
> So getting a dma-buf for the guest backing storage via udmabuf looked
> like a useful approach.  We can export the guest gem buffers to other
> host processes that way.  qemu itself could map it too, to get a linear
> representation of the scattered guest backing storage.
> 
> The other obvious approach would be to do it the other way around and
> allow the guest map the host resource somehow.  On the host side qemu
> could use vgem to allocate resource memory, so it'll be a gem object
> already.  Mapping that into the guest isn't that straight-forward
> though.  The guest manages its physical address space, so the guest
> would need to find a free spot and ask the host to place the resource
> there.  Then the guest needs page structs covering the mapped resource,
> so it can work with it.  Didn't investigate how difficuilt that is.  Use
> memory hotplug maybe?  Can we easily unmap the resource then?  Also I
> think updating the guests physical memory layout (which we would need to
> do on every resource map/unmap) isn't an exactly cheap operation ...

Generally we try to cache mappings as much as possible. And wrt finding a
slot: Create a sufficiently sized BAR on the virgl device, just for that?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [RfC PATCH] Add udmabuf misc device

[Dongwon Kim]

On Fri, Apr 06, 2018 at 03:36:03PM +0300, Oleksandr Andrushchenko wrote:
> On 04/06/2018 02:57 PM, Gerd Hoffmann wrote:
> >   Hi,
> >
> >>>I fail to see any common ground for xen-zcopy and udmabuf ...
> >>Does the above mean you can assume that xen-zcopy and udmabuf
> >>can co-exist as two different solutions?
> >Well, udmabuf route isn't fully clear yet, but yes.
> >
> >See also gvt (intel vgpu), where the hypervisor interface is abstracted
> >away into a separate kernel modules even though most of the actual vgpu
> >emulation code is common.
> Thank you for your input, I'm just trying to figure out
> which of the three z-copy solutions intersect and how much
> >>And what about hyper-dmabuf?

xen z-copy solution is pretty similar fundamentally to hyper_dmabuf
in terms of these core sharing feature:

1. the sharing process - import prime/dmabuf from the producer -> extract
underlying pages and get those shared -> return references for shared pages

2. the page sharing mechanism - it uses Xen-grant-table.

And to give you a quick summary of differences as far as I understand
between two implementations (please correct me if I am wrong, Oleksandr.)

1. xen-zcopy is DRM specific - can import only DRM prime buffer
while hyper_dmabuf can export any dmabuf regardless of originator

2. xen-zcopy doesn't seem to have dma-buf synchronization between two VMs
while (as danvet called it as remote dmabuf api sharing) hyper_dmabuf sends
out synchronization message to the exporting VM for synchronization.

3. 1-level references - when using grant-table for sharing pages, there will
be same # of refs (each 8 byte) as # of shared pages, which is passed to
the userspace to be shared with importing VM in case of xen-zcopy. Compared
to this, hyper_dmabuf does multiple level addressing to generate only one
reference id that represents all shared pages.

4. inter VM messaging (hype_dmabuf only) - hyper_dmabuf has inter-vm msg
communication defined for dmabuf synchronization and private data (meta
info that Matt Roper mentioned) exchange.

5. driver-to-driver notification (hyper_dmabuf only) - importing VM gets
notified when newdmabuf is exported from other VM - uevent can be optionally
generated when this happens.

6. structure - hyper_dmabuf is targetting to provide a generic solution for
inter-domain dmabuf sharing for most hypervisors, which is why it has two
layers as mattrope mentioned, front-end that contains standard API and backend
that is specific to hypervisor.

> >No idea, didn't look at it in detail.
> >
> >Looks pretty complex from a distant view.  Maybe because it tries to
> >build a communication framework using dma-bufs instead of a simple
> >dma-buf passing mechanism.

we started with simple dma-buf sharing but realized there are many
things we need to consider in real use-case, so we added communication
, notification and dma-buf synchronization then re-structured it to 
front-end and back-end (this made things more compicated..) since Xen
was not our only target. Also, we thought passing the reference for the
buffer (hyper_dmabuf_id) is not secure so added uvent mechanism later.

> Yes, I am looking at it now, trying to figure out the full story
> and its implementation. BTW, Intel guys were about to share some
> test application for hyper-dmabuf, maybe I have missed one.
> It could probably better explain the use-cases and the complexity
> they have in hyper-dmabuf.

One example is actually in github. If you want take a look at it, please
visit:

https://github.com/downor/linux_hyper_dmabuf_test/tree/xen/simple_export

> >
> >Like xen-zcopy it seems to depend on the idea that the hypervisor
> >manages all memory it is easy for guests to share pages with the help of
> >the hypervisor.
> So, for xen-zcopy we were not trying to make it generic,
> it just solves display (dumb) zero-copying use-cases for Xen.
> We implemented it as a DRM helper driver because we can't see any
> other use-cases as of now.
> For example, we also have Xen para-virtualized sound driver, but
> its buffer memory usage is not comparable to what display wants
> and it works somewhat differently (e.g. there is no "frame done"
> event, so one can't tell when the sound buffer can be "flipped").
> At the same time, we do not use virtio-gpu, so this could probably
> be one more candidate for shared dma-bufs some day.
> >   Which simply isn't the case on kvm.
> >
> >hyper-dmabuf and xen-zcopy could maybe share code, or hyper-dmabuf build
> >on top of xen-zcopy.
> Hm, I can imagine that: xen-zcopy could be a library code for hyper-dmabuf
> in terms of implementing all that page sharing fun in multiple directions,
> e.g. Host->Guest, Guest->Host, Guest<->Guest.
> But I'll let Matt and Dongwon to comment on that.

I think we can definitely collaborate. Especially, maybe we are using some
outdated sharing mechanism/grant-table mechanism in our Xen backend (thanks
for bringing that up Oleksandr). However, the question is once we collaborate

Re: [RfC PATCH] Add udmabuf misc device

[Oleksandr Andrushchenko]

On 04/06/2018 02:57 PM, Gerd Hoffmann wrote:

   Hi,


I fail to see any common ground for xen-zcopy and udmabuf ...

Does the above mean you can assume that xen-zcopy and udmabuf
can co-exist as two different solutions?

Well, udmabuf route isn't fully clear yet, but yes.

See also gvt (intel vgpu), where the hypervisor interface is abstracted
away into a separate kernel modules even though most of the actual vgpu
emulation code is common.

Thank you for your input, I'm just trying to figure out
which of the three z-copy solutions intersect and how much

And what about hyper-dmabuf?

No idea, didn't look at it in detail.

Looks pretty complex from a distant view.  Maybe because it tries to
build a communication framework using dma-bufs instead of a simple
dma-buf passing mechanism.

Yes, I am looking at it now, trying to figure out the full story
and its implementation. BTW, Intel guys were about to share some
test application for hyper-dmabuf, maybe I have missed one.
It could probably better explain the use-cases and the complexity
they have in hyper-dmabuf.


Like xen-zcopy it seems to depend on the idea that the hypervisor
manages all memory it is easy for guests to share pages with the help of
the hypervisor.

So, for xen-zcopy we were not trying to make it generic,
it just solves display (dumb) zero-copying use-cases for Xen.
We implemented it as a DRM helper driver because we can't see any
other use-cases as of now.
For example, we also have Xen para-virtualized sound driver, but
its buffer memory usage is not comparable to what display wants
and it works somewhat differently (e.g. there is no "frame done"
event, so one can't tell when the sound buffer can be "flipped").
At the same time, we do not use virtio-gpu, so this could probably
be one more candidate for shared dma-bufs some day.

   Which simply isn't the case on kvm.

hyper-dmabuf and xen-zcopy could maybe share code, or hyper-dmabuf build
on top of xen-zcopy.

Hm, I can imagine that: xen-zcopy could be a library code for hyper-dmabuf
in terms of implementing all that page sharing fun in multiple directions,
e.g. Host->Guest, Guest->Host, Guest<->Guest.
But I'll let Matt and Dongwon to comment on that.



cheers,
   Gerd


Thank you,
Oleksandr

P.S. Sorry for making your original mail thread to discuss things much
broader than your RFC...

Re: [RfC PATCH] Add udmabuf misc device

[Gerd Hoffmann]

  Hi,

> > I fail to see any common ground for xen-zcopy and udmabuf ...

> Does the above mean you can assume that xen-zcopy and udmabuf
> can co-exist as two different solutions?

Well, udmabuf route isn't fully clear yet, but yes.

See also gvt (intel vgpu), where the hypervisor interface is abstracted
away into a separate kernel modules even though most of the actual vgpu
emulation code is common.

> And what about hyper-dmabuf?

No idea, didn't look at it in detail.

Looks pretty complex from a distant view.  Maybe because it tries to
build a communication framework using dma-bufs instead of a simple
dma-buf passing mechanism.

Like xen-zcopy it seems to depend on the idea that the hypervisor
manages all memory it is easy for guests to share pages with the help of
the hypervisor.  Which simply isn't the case on kvm.

hyper-dmabuf and xen-zcopy could maybe share code, or hyper-dmabuf build
on top of xen-zcopy.

cheers,
  Gerd

Re: [RfC PATCH] Add udmabuf misc device

[Oleksandr Andrushchenko]

On 04/06/2018 12:07 PM, Gerd Hoffmann wrote:

I'm not sure we can create something which works on both kvm and xen.
The memory management model is quite different ...


On xen the hypervisor manages all memory.  Guests can allow other guests
to access specific pages (using grant tables).  In theory any guest <=>
guest communication is possible.  In practice is mostly guest <=> dom0
because guests access their virtual hardware that way.  dom0 is the
priviledged guest which owns any hardware not managed by xen itself.

Xen guests can ask the hypervisor to update the mapping of guest
physical pages.  They can ballon down (unmap and free pages).  They can
ballon up (ask the hypervisor to map fresh pages).  They can map pages
exported by other guests using grant tables.  xen-zcopy makes heavy use
of this.  It balloons down, to make room in the guest physical address
space, then goes map the exported pages there, finally composes a
dma-buf.


On kvm qemu manages all guest memory.  qemu also has all guest memory
mapped, so a grant-table like mechanism isn't needed to implement
virtual devices.  qemu can decide how it backs memory for the guest.
qemu propagates the guest memory map to the kvm driver in the linux
kernel.  kvm guests have some control over the guest memory map, for
example they can map pci bars wherever they want in their guest physical
address space by programming the base registers accordingly, but unlike
xen guests they can't ask the host to remap individual pages.

Due to qemu having all guest memory mapped virtual devices are typically
designed to have the guest allocate resources, then notify the host
where they are located.  This is where the udmabuf idea comes from:
Guest tells the host (qemu) where the gem object is, and qemu then can
create a dmabuf backed by those pages to pass it on to other processes
such as the wayland display server.  Possibly even without the guest
explicitly asking for it, i.e. export the framebuffer placed by the
guest in the (virtual) vga pci memory bar as dma-buf.  And I can imagine
that this is useful outsize virtualization too.


I fail to see any common ground for xen-zcopy and udmabuf ...

Does the above mean you can assume that xen-zcopy and udmabuf
can co-exist as two different solutions?
And what about hyper-dmabuf?

Thank you,
Oleksandr

Re: [RfC PATCH] Add udmabuf misc device

[Gerd Hoffmann]

On Fri, Apr 06, 2018 at 10:52:21AM +0100, Daniel Stone wrote:
> Hi Gerd,
> 
> On 14 March 2018 at 08:03, Gerd Hoffmann  wrote:
> >> Either mlock account (because it's mlocked defacto), and get_user_pages
> >> won't do that for you.
> >>
> >> Or you write the full-blown userptr implementation, including mmu_notifier
> >> support (see i915 or amdgpu), but that also requires Christian Königs
> >> latest ->invalidate_mapping RFC for dma-buf (since atm exporting userptr
> >> buffers is a no-go).
> >
> > I guess I'll look at mlock accounting for starters then.  Easier for
> > now, and leaves the door open to switch to userptr later as this should
> > be transparent to userspace.
> 
> Out of interest, do you have usecases for full userptr support? Maybe
> another way would be to allow creation of dmabufs from memfds.

I have two things in mind.

One is vga emulation.  I have virtual pci memory bar for the virtual
vga.  qemu backs vga memory with anonymous pages right now, switching
that to shmem should be easy though if that makes things easier.  Guest
places the framebuffer somewhere in the pci bar, and I want export the
chunk which represents the framebuffer as dma-buf to display it on the
host without copying around data.  Framebuffer is linear in guest
physical memory, so a single block only.  That is the simpler case.

The more difficuilt one is virtio-gpu ressources.  virtio-gpu resources
live in host memory (guest has no direct access).  The guest can
optionally specify guest memory pages as backing storage for the
resource.  Guest backing storage is allowed to be scattered.  Commands
exist to copy both ways between host storage and guest backing.

With virgl (opengl acceleration) enabled the guest will send rendering
commands to fill the framebuffer ressource, so there is no need to copy
content to the framebuffer ressource.  The guest may fill other
resources such as textures used for rendering with copy commands.

Without acceleration the guest does software-rendering to the backing
storage, then sends a command to copy the framebuffer content from guest
backing storage to host ressource.

Now it would be useful to allow a shared mapping, so no copying between
guest backing storage and host resource is needed, especially for the
software rendering case (i.e. dumb gem buffers).  Being able to export
guest dumb buffers to other host processes would be useful too, for
example to display guest windows seamlessly on the host wayland server.

So getting a dma-buf for the guest backing storage via udmabuf looked
like a useful approach.  We can export the guest gem buffers to other
host processes that way.  qemu itself could map it too, to get a linear
representation of the scattered guest backing storage.

The other obvious approach would be to do it the other way around and
allow the guest map the host resource somehow.  On the host side qemu
could use vgem to allocate resource memory, so it'll be a gem object
already.  Mapping that into the guest isn't that straight-forward
though.  The guest manages its physical address space, so the guest
would need to find a free spot and ask the host to place the resource
there.  Then the guest needs page structs covering the mapped resource,
so it can work with it.  Didn't investigate how difficuilt that is.  Use
memory hotplug maybe?  Can we easily unmap the resource then?  Also I
think updating the guests physical memory layout (which we would need to
do on every resource map/unmap) isn't an exactly cheap operation ...

cheers,
  Gerd

Re: [RfC PATCH] Add udmabuf misc device

[Daniel Stone]

Hi Gerd,

On 14 March 2018 at 08:03, Gerd Hoffmann  wrote:
>> Either mlock account (because it's mlocked defacto), and get_user_pages
>> won't do that for you.
>>
>> Or you write the full-blown userptr implementation, including mmu_notifier
>> support (see i915 or amdgpu), but that also requires Christian Königs
>> latest ->invalidate_mapping RFC for dma-buf (since atm exporting userptr
>> buffers is a no-go).
>
> I guess I'll look at mlock accounting for starters then.  Easier for
> now, and leaves the door open to switch to userptr later as this should
> be transparent to userspace.

Out of interest, do you have usecases for full userptr support? Maybe
another way would be to allow creation of dmabufs from memfds.

Cheers,
Daniel

Re: [RfC PATCH] Add udmabuf misc device

[Oleksandr Andrushchenko]

On 04/06/2018 12:07 PM, Gerd Hoffmann wrote:

   Hi,


   * The general interface should be able to express sharing from any
 guest:guest, not just guest:host.  Arbitrary G:G sharing might be
 something some hypervisors simply aren't able to support, but the
 userspace API itself shouldn't make assumptions or restrict that.  I
 think ideally the sharing API would include some kind of
 query_targets interface that would return a list of VM's that your
 current OS is allowed to share with; that list would be depend on the
 policy established by the system integrator, but obviously wouldn't
 include targets that the hypervisor itself wouldn't be capable of
 handling.

Can you give a use-case for this? I mean that the system integrator
is the one who defines which guests/hosts talk to each other,
but querying means that it is possible that VMs have some sort
of discovery mechanism, so they can decide on their own whom
to connect to.

Note that vsock (created by vmware, these days also has a virtio
transport for kvm) started with support for both guest <=> host and
guest <=> guest support.  But later on guest <=> guest was dropped.
As far I know the reasons where (a) lack of use cases and (b) security.

So, I likewise would know more details on the use cases you have in mind
here.  Unless we have a compelling use case here I'd suggest to drop the
guest <=> guest requirement as it makes the whole thing alot more
complex.

This is exactly the use-case we have: in our setup Dom0 doesn't
own any HW at all and all the HW is passed into a dedicated
driver domain (DomD) which is still a guest domain.
Then, buffers are shared between two guests, for example,
DomD and DomA (Android guest)

   * The sharing API could be used to share multiple kinds of content in a
 single system.  The sharing sink driver running in the content
 producer's VM should accept some additional metadata that will be
 passed over to the target VM as well.

Not sure this should be part of hyper-dmabuf.  A dma-buf is nothing but
a block of data, period.  Therefore protocols with dma-buf support
(wayland for example) typically already send over metadata describing
the content, so duplicating that in hyper-dmabuf looks pointless.


1. We are targeting ARM and one of the major requirements for the buffer
sharing is the ability to allocate physically contiguous buffers, which gets
even more complicated for systems not backed with an IOMMU. So, for some
use-cases it is enough to make the buffers contiguous in terms of IPA and
sometimes those need to be contiguous in terms of PA.

Which pretty much implies the host must to the allocation.


2. For Xen we would love to see UAPI to create a dma-buf from grant
references provided, so we can use this generic solution to implement
zero-copying without breaking the existing Xen protocols. This can
probably be extended to other hypervizors as well.

I'm not sure we can create something which works on both kvm and xen.
The memory management model is quite different ...


On xen the hypervisor manages all memory.  Guests can allow other guests
to access specific pages (using grant tables).  In theory any guest <=>
guest communication is possible.  In practice is mostly guest <=> dom0
because guests access their virtual hardware that way.  dom0 is the
priviledged guest which owns any hardware not managed by xen itself.

Please see above for our setup with DomD and Dom0 being
a generic ARMv8 domain, no HW

Xen guests can ask the hypervisor to update the mapping of guest
physical pages.  They can ballon down (unmap and free pages).  They can
ballon up (ask the hypervisor to map fresh pages).  They can map pages
exported by other guests using grant tables.  xen-zcopy makes heavy use
of this.  It balloons down, to make room in the guest physical address
space, then goes map the exported pages there, finally composes a
dma-buf.

This is what it does


On kvm qemu manages all guest memory.  qemu also has all guest memory
mapped, so a grant-table like mechanism isn't needed to implement
virtual devices.  qemu can decide how it backs memory for the guest.
qemu propagates the guest memory map to the kvm driver in the linux
kernel.  kvm guests have some control over the guest memory map, for
example they can map pci bars wherever they want in their guest physical
address space by programming the base registers accordingly, but unlike
xen guests they can't ask the host to remap individual pages.

Due to qemu having all guest memory mapped virtual devices are typically
designed to have the guest allocate resources, then notify the host
where they are located.  This is where the udmabuf idea comes from:
Guest tells the host (qemu) where the gem object is, and qemu then can
create a dmabuf backed by those pages to pass it on to other processes
such as the wayland display server.  Possibly even without the guest
explicitly asking for it, i.e. export the framebuffer placed by the

Re: [RfC PATCH] Add udmabuf misc device

[Gerd Hoffmann]

  Hi,

> >   * The general interface should be able to express sharing from any
> > guest:guest, not just guest:host.  Arbitrary G:G sharing might be
> > something some hypervisors simply aren't able to support, but the
> > userspace API itself shouldn't make assumptions or restrict that.  I
> > think ideally the sharing API would include some kind of
> > query_targets interface that would return a list of VM's that your
> > current OS is allowed to share with; that list would be depend on the
> > policy established by the system integrator, but obviously wouldn't
> > include targets that the hypervisor itself wouldn't be capable of
> > handling.

> Can you give a use-case for this? I mean that the system integrator
> is the one who defines which guests/hosts talk to each other,
> but querying means that it is possible that VMs have some sort
> of discovery mechanism, so they can decide on their own whom
> to connect to.

Note that vsock (created by vmware, these days also has a virtio
transport for kvm) started with support for both guest <=> host and
guest <=> guest support.  But later on guest <=> guest was dropped.
As far I know the reasons where (a) lack of use cases and (b) security.

So, I likewise would know more details on the use cases you have in mind
here.  Unless we have a compelling use case here I'd suggest to drop the
guest <=> guest requirement as it makes the whole thing alot more
complex.

> >   * The sharing API could be used to share multiple kinds of content in a
> > single system.  The sharing sink driver running in the content
> > producer's VM should accept some additional metadata that will be
> > passed over to the target VM as well.

Not sure this should be part of hyper-dmabuf.  A dma-buf is nothing but
a block of data, period.  Therefore protocols with dma-buf support
(wayland for example) typically already send over metadata describing
the content, so duplicating that in hyper-dmabuf looks pointless.

> 1. We are targeting ARM and one of the major requirements for the buffer
> sharing is the ability to allocate physically contiguous buffers, which gets
> even more complicated for systems not backed with an IOMMU. So, for some
> use-cases it is enough to make the buffers contiguous in terms of IPA and
> sometimes those need to be contiguous in terms of PA.

Which pretty much implies the host must to the allocation.

> 2. For Xen we would love to see UAPI to create a dma-buf from grant
> references provided, so we can use this generic solution to implement
> zero-copying without breaking the existing Xen protocols. This can
> probably be extended to other hypervizors as well.

I'm not sure we can create something which works on both kvm and xen.
The memory management model is quite different ...


On xen the hypervisor manages all memory.  Guests can allow other guests
to access specific pages (using grant tables).  In theory any guest <=>
guest communication is possible.  In practice is mostly guest <=> dom0
because guests access their virtual hardware that way.  dom0 is the
priviledged guest which owns any hardware not managed by xen itself.

Xen guests can ask the hypervisor to update the mapping of guest
physical pages.  They can ballon down (unmap and free pages).  They can
ballon up (ask the hypervisor to map fresh pages).  They can map pages
exported by other guests using grant tables.  xen-zcopy makes heavy use
of this.  It balloons down, to make room in the guest physical address
space, then goes map the exported pages there, finally composes a
dma-buf.


On kvm qemu manages all guest memory.  qemu also has all guest memory
mapped, so a grant-table like mechanism isn't needed to implement
virtual devices.  qemu can decide how it backs memory for the guest.
qemu propagates the guest memory map to the kvm driver in the linux
kernel.  kvm guests have some control over the guest memory map, for
example they can map pci bars wherever they want in their guest physical
address space by programming the base registers accordingly, but unlike
xen guests they can't ask the host to remap individual pages.

Due to qemu having all guest memory mapped virtual devices are typically
designed to have the guest allocate resources, then notify the host
where they are located.  This is where the udmabuf idea comes from:
Guest tells the host (qemu) where the gem object is, and qemu then can
create a dmabuf backed by those pages to pass it on to other processes
such as the wayland display server.  Possibly even without the guest
explicitly asking for it, i.e. export the framebuffer placed by the
guest in the (virtual) vga pci memory bar as dma-buf.  And I can imagine
that this is useful outsize virtualization too.


I fail to see any common ground for xen-zcopy and udmabuf ...

Beside that there is the problem that the udmabuf idea has its own share
of issues, for example the fork() issue pointed out by Christian
König[1].  So I still need to 

Re: [RfC PATCH] Add udmabuf misc device

[Oleksandr Andrushchenko]

On 04/06/2018 03:11 AM, Matt Roper wrote:

On Thu, Apr 05, 2018 at 10:32:04PM +0200, Daniel Vetter wrote:

Pulling this out of the shadows again.

We now also have xen-zcopy from Oleksandr and the hyper dmabuf stuff
from Matt and Dongwong.

At least from the intel side there seems to be the idea to just have 1
special device that can handle cross-gues/host sharing for all kinds
of hypervisors, so I guess you all need to work together :-)

Or we throw out the idea that hyper dmabuf will be cross-hypervisor
(not sure how useful/reasonable that is, someone please convince me
one way or the other).

Cheers, Daniel

Dongwon (DW) is the one doing all the real work on hyper_dmabuf, but I'm
familiar with the use cases he's trying to address, and I think there
are a couple high-level goals of his work that are worth calling out as
we discuss the various options for sharing buffers produced in one VM
with a consumer running in another VM:

  * We should try to keep the interface/usage separate from the
underlying hypervisor implementation details.  I.e., in DW's design
the sink/source drivers that handle the actual buffer passing in the
two VM's should provide a generic interface that does not depend on a
specific hypervisor.

This is what we did for display, sound and multi-touch on Xen:
we have implemented generic protocols which are OS agnostic.
Have you started prototyping such a protocol for hyper-dmabuf yet?


  Behind the scenes there could be various
implementations for specific hypervisors (Xen, KVM, ACRN, etc.), and
some of those backends may have additional restrictions, but it would
be best if userspace didn't have to know the specific hypervisor
running on the system and could just query the general capabilities
available to it.  We've already got projects in flight that are
wanting this functionality on Xen and ACRN today.

Should we add corresponding communities into discussion then?



  * The general interface should be able to express sharing from any
guest:guest, not just guest:host.  Arbitrary G:G sharing might be
something some hypervisors simply aren't able to support, but the
userspace API itself shouldn't make assumptions or restrict that.  I
think ideally the sharing API would include some kind of
query_targets interface that would return a list of VM's that your
current OS is allowed to share with; that list would be depend on the
policy established by the system integrator, but obviously wouldn't
include targets that the hypervisor itself wouldn't be capable of
handling.

Can you give a use-case for this? I mean that the system integrator
is the one who defines which guests/hosts talk to each other,
but querying means that it is possible that VMs have some sort
of discovery mechanism, so they can decide on their own whom
to connect to.

  * A lot of the initial use cases are in the realm of graphics, but this

shouldn't be a graphics-specific API.  Buffers might contain other
types of content as well (e.g., audio).  Really the content producer
could potentially be any driver (or userspace) running in the VM that
knows how to import/export dma_buf's (or maybe just import given
danvet's suggestion that we should make the sink driver do all the
actual memory allocation for any buffers that may be shared).

  * We need to be able to handle cross-VM coordination of buffer usage as
well, so I think we'd want to include fence forwarding support in the
API as well to signal back and forth about production/consumption
completion.  And of course document really well what should happen
if, for example, the entire VM you're sharing with/from dies.

  * The sharing API could be used to share multiple kinds of content in a
single system.  The sharing sink driver running in the content
producer's VM should accept some additional metadata that will be
passed over to the target VM as well.  The sharing source driver
running in the content consumer's VM would then be able to use this
metadata to determine the purpose of a new buffer that arrives and
filter/dispatch it to the appropriate consumer.


For reference, the terminology I'm using is

  /--\  dma_buf   /--\ HV /\  dma_buf   /--\
  | Producer |--->| Sink | HV | Source |--->| Consumer |
  \--/   ioctls   \--/ HV \/  uevents   \--/



In the realm of graphics, "Producer" could potentially be something like
an EGL client that sends the buffer at context setup and then signals
with fences on each SwapBuffers.  "Consumer" could be a Wayland client
that proxies the buffers into surfaces or dispatches them to other
userspace software that's waiting for buffers.

With the hyper_dmabuf approach, there's a lot of ABI details that need
to be worked out and really clearly documented before we worry too much
about the backend hypervisor-specific 

Re: [RfC PATCH] Add udmabuf misc device

[Matt Roper]

On Thu, Apr 05, 2018 at 10:32:04PM +0200, Daniel Vetter wrote:
> Pulling this out of the shadows again.
> 
> We now also have xen-zcopy from Oleksandr and the hyper dmabuf stuff
> from Matt and Dongwong.
> 
> At least from the intel side there seems to be the idea to just have 1
> special device that can handle cross-gues/host sharing for all kinds
> of hypervisors, so I guess you all need to work together :-)
> 
> Or we throw out the idea that hyper dmabuf will be cross-hypervisor
> (not sure how useful/reasonable that is, someone please convince me
> one way or the other).
> 
> Cheers, Daniel

Dongwon (DW) is the one doing all the real work on hyper_dmabuf, but I'm
familiar with the use cases he's trying to address, and I think there
are a couple high-level goals of his work that are worth calling out as
we discuss the various options for sharing buffers produced in one VM
with a consumer running in another VM:

 * We should try to keep the interface/usage separate from the
   underlying hypervisor implementation details.  I.e., in DW's design
   the sink/source drivers that handle the actual buffer passing in the
   two VM's should provide a generic interface that does not depend on a
   specific hypervisor.  Behind the scenes there could be various
   implementations for specific hypervisors (Xen, KVM, ACRN, etc.), and
   some of those backends may have additional restrictions, but it would
   be best if userspace didn't have to know the specific hypervisor
   running on the system and could just query the general capabilities
   available to it.  We've already got projects in flight that are
   wanting this functionality on Xen and ACRN today.

 * The general interface should be able to express sharing from any
   guest:guest, not just guest:host.  Arbitrary G:G sharing might be
   something some hypervisors simply aren't able to support, but the
   userspace API itself shouldn't make assumptions or restrict that.  I
   think ideally the sharing API would include some kind of
   query_targets interface that would return a list of VM's that your
   current OS is allowed to share with; that list would be depend on the
   policy established by the system integrator, but obviously wouldn't
   include targets that the hypervisor itself wouldn't be capable of
   handling.
   
 * A lot of the initial use cases are in the realm of graphics, but this
   shouldn't be a graphics-specific API.  Buffers might contain other
   types of content as well (e.g., audio).  Really the content producer
   could potentially be any driver (or userspace) running in the VM that
   knows how to import/export dma_buf's (or maybe just import given
   danvet's suggestion that we should make the sink driver do all the
   actual memory allocation for any buffers that may be shared).

 * We need to be able to handle cross-VM coordination of buffer usage as
   well, so I think we'd want to include fence forwarding support in the
   API as well to signal back and forth about production/consumption
   completion.  And of course document really well what should happen
   if, for example, the entire VM you're sharing with/from dies.

 * The sharing API could be used to share multiple kinds of content in a
   single system.  The sharing sink driver running in the content
   producer's VM should accept some additional metadata that will be
   passed over to the target VM as well.  The sharing source driver
   running in the content consumer's VM would then be able to use this
   metadata to determine the purpose of a new buffer that arrives and
   filter/dispatch it to the appropriate consumer.


For reference, the terminology I'm using is

 /--\  dma_buf   /--\ HV /\  dma_buf   /--\
 | Producer |--->| Sink | HV | Source |--->| Consumer |
 \--/   ioctls   \--/ HV \/  uevents   \--/



In the realm of graphics, "Producer" could potentially be something like
an EGL client that sends the buffer at context setup and then signals
with fences on each SwapBuffers.  "Consumer" could be a Wayland client
that proxies the buffers into surfaces or dispatches them to other
userspace software that's waiting for buffers.

With the hyper_dmabuf approach, there's a lot of ABI details that need
to be worked out and really clearly documented before we worry too much
about the backend hypervisor-specific stuff.

I'm not super familiar with xen-zcopy and udmabuf, but it sounds like
they're approaching similar problems from slightly different directions,
so we should make sure we can come up with something that satisfies
everyone's requirements. 


Matt

> 
> On Wed, Mar 14, 2018 at 9:03 AM, Gerd Hoffmann  wrote:
> >   Hi,
> >
> >> Either mlock account (because it's mlocked defacto), and get_user_pages
> >> won't do that for you.
> >>
> >> Or you write the full-blown userptr implementation, including mmu_notifier
> >> support (see i915 or amdgpu), but that also requires 

Re: [RfC PATCH] Add udmabuf misc device

[Daniel Vetter]

Pulling this out of the shadows again.

We now also have xen-zcopy from Oleksandr and the hyper dmabuf stuff
from Matt and Dongwong.

At least from the intel side there seems to be the idea to just have 1
special device that can handle cross-gues/host sharing for all kinds
of hypervisors, so I guess you all need to work together :-)

Or we throw out the idea that hyper dmabuf will be cross-hypervisor
(not sure how useful/reasonable that is, someone please convince me
one way or the other).

Cheers, Daniel

On Wed, Mar 14, 2018 at 9:03 AM, Gerd Hoffmann  wrote:
>   Hi,
>
>> Either mlock account (because it's mlocked defacto), and get_user_pages
>> won't do that for you.
>>
>> Or you write the full-blown userptr implementation, including mmu_notifier
>> support (see i915 or amdgpu), but that also requires Christian Königs
>> latest ->invalidate_mapping RFC for dma-buf (since atm exporting userptr
>> buffers is a no-go).
>
> I guess I'll look at mlock accounting for starters then.  Easier for
> now, and leaves the door open to switch to userptr later as this should
> be transparent to userspace.
>
>> > Known issue:  Driver API isn't complete yet.  Need add some flags, for
>> > example to support read-only buffers.
>>
>> dma-buf has no concept of read-only. I don't think we can even enforce
>> that (not many iommus can enforce this iirc), so pretty much need to
>> require r/w memory.
>
> Ah, ok.  Just saw the 'write' arg for get_user_pages_fast and figured we
> might support that, but if iommus can't handle that anyway it's
> pointless indeed.
>
>> > Cc: David Airlie 
>> > Cc: Tomeu Vizoso 
>> > Signed-off-by: Gerd Hoffmann 
>>
>> btw there's also the hyperdmabuf stuff from the xen folks, but imo their
>> solution of forwarding the entire dma-buf api is over the top. This here
>> looks _much_ better, pls cc all the hyperdmabuf people on your next
>> version.
>
> Fun fact: googling for "hyperdmabuf" found me your mail and nothing else :-o
> (Trying "hyper dmabuf" instead worked better then).
>
> Yes, will cc them on the next version.  Not sure it'll help much on xen
> though due to the memory management being very different.  Basically xen
> owns the memory, not the kernel of the control domain (dom0), so
> creating dmabufs for guest memory chunks isn't that simple ...
>
> Also it's not clear whenever they really need guest -> guest exports or
> guest -> dom0 exports.
>
>> Overall I like the idea, but too lazy to review.
>
> Cool.  General comments on the idea was all I was looking for for the
> moment.  Spare yor review cycles for the next version ;)
>
>> Oh, some kselftests for this stuff would be lovely.
>
> I'll look into it.
>
> thanks,
>   Gerd
>
> ___
> dri-devel mailing list
> dri-de...@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel



-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch

Re: [RfC PATCH] Add udmabuf misc device

[Gerd Hoffmann]

  Hi,

> Either mlock account (because it's mlocked defacto), and get_user_pages
> won't do that for you.
> 
> Or you write the full-blown userptr implementation, including mmu_notifier
> support (see i915 or amdgpu), but that also requires Christian Königs
> latest ->invalidate_mapping RFC for dma-buf (since atm exporting userptr
> buffers is a no-go).

I guess I'll look at mlock accounting for starters then.  Easier for
now, and leaves the door open to switch to userptr later as this should
be transparent to userspace.

> > Known issue:  Driver API isn't complete yet.  Need add some flags, for
> > example to support read-only buffers.
> 
> dma-buf has no concept of read-only. I don't think we can even enforce
> that (not many iommus can enforce this iirc), so pretty much need to
> require r/w memory.

Ah, ok.  Just saw the 'write' arg for get_user_pages_fast and figured we
might support that, but if iommus can't handle that anyway it's
pointless indeed.

> > Cc: David Airlie 
> > Cc: Tomeu Vizoso 
> > Signed-off-by: Gerd Hoffmann 
> 
> btw there's also the hyperdmabuf stuff from the xen folks, but imo their
> solution of forwarding the entire dma-buf api is over the top. This here
> looks _much_ better, pls cc all the hyperdmabuf people on your next
> version.

Fun fact: googling for "hyperdmabuf" found me your mail and nothing else :-o
(Trying "hyper dmabuf" instead worked better then).

Yes, will cc them on the next version.  Not sure it'll help much on xen
though due to the memory management being very different.  Basically xen
owns the memory, not the kernel of the control domain (dom0), so
creating dmabufs for guest memory chunks isn't that simple ...

Also it's not clear whenever they really need guest -> guest exports or
guest -> dom0 exports.

> Overall I like the idea, but too lazy to review.

Cool.  General comments on the idea was all I was looking for for the
moment.  Spare yor review cycles for the next version ;)

> Oh, some kselftests for this stuff would be lovely.

I'll look into it.

thanks,
  Gerd

Re: [RfC PATCH] Add udmabuf misc device

[Daniel Vetter]

On Tue, Mar 13, 2018 at 04:48:26PM +0100, Gerd Hoffmann wrote:
> A driver to let userspace turn iovecs into dma-bufs.
> 
> Use case:  Allows qemu pass around dmabufs for the guest framebuffer.
> https://www.kraxel.org/cgit/qemu/log/?h=sirius/udmabuf has an
> experimental patch.
> 
> Also allows qemu to export guest virtio-gpu resources as host dmabufs.
> Should be possible to use it to display guest wayland windows on the
> host display server.  virtio-gpu ressources can be chunked so we will
> actually need multiple iovec entries.  UNTESTED.
> 
> Want collect some feedback on the general approach with this RfC series.
> Can this work?  If not, better ideas?
> 
> Question:  Must this be hooked into some kind of mlock accounting, to
> limit the amout of memory userspace is allowed to pin this way?  Or will
> get_user_pages_fast() handle that for me?

Either mlock account (because it's mlocked defacto), and get_user_pages
won't do that for you.

Or you write the full-blown userptr implementation, including mmu_notifier
support (see i915 or amdgpu), but that also requires Christian Königs
latest ->invalidate_mapping RFC for dma-buf (since atm exporting userptr
buffers is a no-go).

> 
> Known issue:  Driver API isn't complete yet.  Need add some flags, for
> example to support read-only buffers.

dma-buf has no concept of read-only. I don't think we can even enforce
that (not many iommus can enforce this iirc), so pretty much need to
require r/w memory.

> Cc: David Airlie 
> Cc: Tomeu Vizoso 
> Signed-off-by: Gerd Hoffmann 

btw there's also the hyperdmabuf stuff from the xen folks, but imo their
solution of forwarding the entire dma-buf api is over the top. This here
looks _much_ better, pls cc all the hyperdmabuf people on your next
version.

Overall I like the idea, but too lazy to review. Can maybe be bribed :-)

Oh, some kselftests for this stuff would be lovely.
-Daniel
> ---
>  include/uapi/linux/udmabuf.h |  21 
>  drivers/dma-buf/udmabuf.c| 250 
> +++
>  drivers/dma-buf/Kconfig  |   7 ++
>  drivers/dma-buf/Makefile |   1 +
>  4 files changed, 279 insertions(+)
>  create mode 100644 include/uapi/linux/udmabuf.h
>  create mode 100644 drivers/dma-buf/udmabuf.c
> 
> diff --git a/include/uapi/linux/udmabuf.h b/include/uapi/linux/udmabuf.h
> new file mode 100644
> index 00..fd2fa441fe
> --- /dev/null
> +++ b/include/uapi/linux/udmabuf.h
> @@ -0,0 +1,21 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +#ifndef _UAPI_LINUX_UDMABUF_H
> +#define _UAPI_LINUX_UDMABUF_H
> +
> +#include 
> +#include 
> +
> +struct udmabuf_iovec {
> + __u64 base;
> + __u64 len;
> +};
> +
> +struct udmabuf_create {
> + __u32 flags;
> + __u32 niov;
> + struct udmabuf_iovec iovs[];
> +};
> +
> +#define UDMABUF_CREATE _IOW(0x42, 0x23, struct udmabuf_create)
> +
> +#endif /* _UAPI_LINUX_UDMABUF_H */
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> new file mode 100644
> index 00..ec012d7ac7
> --- /dev/null
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -0,0 +1,250 @@
> +/*
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +#include 
> +#include 
> +#include 
> +#include 
> +#include 
> +#include 
> +#include 
> +#include 
> +
> +#include 
> +
> +struct udmabuf {
> + u32 pagecount;
> + struct page **pages;
> +};
> +
> +static int udmabuf_vm_fault(struct vm_fault *vmf)
> +{
> + struct vm_area_struct *vma = vmf->vma;
> + struct udmabuf *ubuf = vma->vm_private_data;
> +
> + if (WARN_ON(vmf->pgoff >= ubuf->pagecount))
> + return VM_FAULT_SIGBUS;
> +
> + vmf->page = ubuf->pages[vmf->pgoff];
> + get_page(vmf->page);
> + return 0;
> +}
> +
> +static const struct vm_operations_struct udmabuf_vm_ops = {
> + .fault = udmabuf_vm_fault,
> +};
> +
> +static int mmap_udmabuf(struct dma_buf *buf, struct vm_area_struct *vma)
> +{
> + struct udmabuf *ubuf = buf->priv;
> +
> + if ((vma->vm_flags & VM_SHARED) == 0)
> + return -EINVAL;
> +
> + vma->vm_ops = _vm_ops;
> + vma->vm_private_data = ubuf;
> + return 0;
> +}
> +
> +static struct sg_table *map_udmabuf(struct dma_buf_attachment *at,
> + enum dma_data_direction direction)
> +{
> + struct udmabuf *ubuf = at->dmabuf->priv;
> + struct sg_table *sg;
> +
> + sg = kzalloc(sizeof(*sg), GFP_KERNEL);
> + if (!sg)
> + goto err1;
> + if (sg_alloc_table_from_pages(sg, ubuf->pages, ubuf->pagecount,
> +   0, ubuf->pagecount << PAGE_SHIFT,
> +   GFP_KERNEL) < 0)
> + goto err2;
> + if (!dma_map_sg(at->dev, sg->sgl, sg->nents, direction))
> + 

[RfC PATCH] Add udmabuf misc device

[Gerd Hoffmann]

A driver to let userspace turn iovecs into dma-bufs.

Use case:  Allows qemu pass around dmabufs for the guest framebuffer.
https://www.kraxel.org/cgit/qemu/log/?h=sirius/udmabuf has an
experimental patch.

Also allows qemu to export guest virtio-gpu resources as host dmabufs.
Should be possible to use it to display guest wayland windows on the
host display server.  virtio-gpu ressources can be chunked so we will
actually need multiple iovec entries.  UNTESTED.

Want collect some feedback on the general approach with this RfC series.
Can this work?  If not, better ideas?

Question:  Must this be hooked into some kind of mlock accounting, to
limit the amout of memory userspace is allowed to pin this way?  Or will
get_user_pages_fast() handle that for me?

Known issue:  Driver API isn't complete yet.  Need add some flags, for
example to support read-only buffers.

Cc: David Airlie 
Cc: Tomeu Vizoso 
Signed-off-by: Gerd Hoffmann 
---
 include/uapi/linux/udmabuf.h |  21 
 drivers/dma-buf/udmabuf.c| 250 +++
 drivers/dma-buf/Kconfig  |   7 ++
 drivers/dma-buf/Makefile |   1 +
 4 files changed, 279 insertions(+)
 create mode 100644 include/uapi/linux/udmabuf.h
 create mode 100644 drivers/dma-buf/udmabuf.c

diff --git a/include/uapi/linux/udmabuf.h b/include/uapi/linux/udmabuf.h
new file mode 100644
index 00..fd2fa441fe
--- /dev/null
+++ b/include/uapi/linux/udmabuf.h
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_LINUX_UDMABUF_H
+#define _UAPI_LINUX_UDMABUF_H
+
+#include 
+#include 
+
+struct udmabuf_iovec {
+   __u64 base;
+   __u64 len;
+};
+
+struct udmabuf_create {
+   __u32 flags;
+   __u32 niov;
+   struct udmabuf_iovec iovs[];
+};
+
+#define UDMABUF_CREATE _IOW(0x42, 0x23, struct udmabuf_create)
+
+#endif /* _UAPI_LINUX_UDMABUF_H */
diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
new file mode 100644
index 00..ec012d7ac7
--- /dev/null
+++ b/drivers/dma-buf/udmabuf.c
@@ -0,0 +1,250 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+
+#include 
+
+struct udmabuf {
+   u32 pagecount;
+   struct page **pages;
+};
+
+static int udmabuf_vm_fault(struct vm_fault *vmf)
+{
+   struct vm_area_struct *vma = vmf->vma;
+   struct udmabuf *ubuf = vma->vm_private_data;
+
+   if (WARN_ON(vmf->pgoff >= ubuf->pagecount))
+   return VM_FAULT_SIGBUS;
+
+   vmf->page = ubuf->pages[vmf->pgoff];
+   get_page(vmf->page);
+   return 0;
+}
+
+static const struct vm_operations_struct udmabuf_vm_ops = {
+   .fault = udmabuf_vm_fault,
+};
+
+static int mmap_udmabuf(struct dma_buf *buf, struct vm_area_struct *vma)
+{
+   struct udmabuf *ubuf = buf->priv;
+
+   if ((vma->vm_flags & VM_SHARED) == 0)
+   return -EINVAL;
+
+   vma->vm_ops = _vm_ops;
+   vma->vm_private_data = ubuf;
+   return 0;
+}
+
+static struct sg_table *map_udmabuf(struct dma_buf_attachment *at,
+   enum dma_data_direction direction)
+{
+   struct udmabuf *ubuf = at->dmabuf->priv;
+   struct sg_table *sg;
+
+   sg = kzalloc(sizeof(*sg), GFP_KERNEL);
+   if (!sg)
+   goto err1;
+   if (sg_alloc_table_from_pages(sg, ubuf->pages, ubuf->pagecount,
+ 0, ubuf->pagecount << PAGE_SHIFT,
+ GFP_KERNEL) < 0)
+   goto err2;
+   if (!dma_map_sg(at->dev, sg->sgl, sg->nents, direction))
+   goto err3;
+
+   return sg;
+
+err3:
+   sg_free_table(sg);
+err2:
+   kfree(sg);
+err1:
+   return ERR_PTR(-ENOMEM);
+}
+
+static void unmap_udmabuf(struct dma_buf_attachment *at,
+ struct sg_table *sg,
+ enum dma_data_direction direction)
+{
+   sg_free_table(sg);
+   kfree(sg);
+}
+
+static void release_udmabuf(struct dma_buf *buf)
+{
+   struct udmabuf *ubuf = buf->priv;
+   pgoff_t pg;
+
+   for (pg = 0; pg < ubuf->pagecount; pg++)
+   put_page(ubuf->pages[pg]);
+   kfree(ubuf->pages);
+   kfree(ubuf);
+}
+
+static void *kmap_atomic_udmabuf(struct dma_buf *buf, unsigned long offset)
+{
+   struct udmabuf *ubuf = buf->priv;
+   struct page *page = ubuf->pages[offset >> PAGE_SHIFT];
+
+   return kmap_atomic(page);
+}
+
+static void *kmap_udmabuf(struct dma_buf *buf, unsigned long offset)
+{
+   struct udmabuf *ubuf = buf->priv;
+   struct page *page = ubuf->pages[offset >> PAGE_SHIFT];
+
+   return kmap(page);
+}
+
+static struct dma_buf_ops udmabuf_ops = {
+