Re: [PATCH 1/1] GetMemoryMap(), handling of no-map DT property

[Grant Likely]

On 15/09/2020 17:00, Heinrich Schuchardt wrote:

On 15.09.20 16:50, Grant Likely wrote:



On 15/09/2020 15:36, Heinrich Schuchardt wrote:

On 15.09.20 16:16, Ard Biesheuvel wrote:
[...] EfiRuntimeServicesData is not covered by the linear map, but 
will map

it in the EFI page tables for access by the firmware itself at
runtime, so it is not an option here.



The device-tree spec specifically says /mmemreserve/ serve to "define an
entry for the devicetree blob’s memory reservation table."


I think this is just poorly worded. It would be better written as:
     "Memory reservations create entries in the devicetree blob’s
     memory reservation table."


Shouldn't the description of /memreserve/ refer to chapter 5.3 Memory
Reservation Block? E.g.

"Memory reservations blocks (see chapter 5.3) are represented by lines
of the form

 /memreserve/  ;

where  and  are 64-bit C-style integers, e.g.

 /memreserve/ 0x1000 0x0004000;"


I like that language & layout. I've pulled it into the draft patch. Thanks!


Some requirements in chapter 5.3.1 sound similar to the description of
the no-map sub-nodes of /reserved-memory, e.g. speculative access is
prohibited:

"Any memory that is declared in a memory node and is accessed by the
boot program or caused to be accessed by the boot program after client
entry must be reserved. Examples of this type of access include (e.g.,
speculative memory reads through a non-guarded virtual page)."

So in line with our discussion concerning no-map EfiReservedMemoryType
seems the most appropriate.

UEFI runtime drivers will be relocated by SetVirtualMemoryMap(). So the
requirement in the above citation does not make much sense for memory
that is EfiRuntimeServicesCode or EfiRuntimeServicesData. So those
should not be modeled as /memreserve/. Just another issue with the DT spec.


Okay. I'm convinced. I'll specify EfiReservedMemoryType for memreserve.

g.

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Re: [PATCH 1/1] GetMemoryMap(), handling of no-map DT property

[Heinrich Schuchardt]

On 15.09.20 16:50, Grant Likely wrote:
>
>
> On 15/09/2020 15:36, Heinrich Schuchardt wrote:
>> On 15.09.20 16:16, Ard Biesheuvel wrote:
>>> On Tue, 15 Sep 2020 at 17:05, Grant Likely  wrote:



 On 15/09/2020 14:46, Leif Lindholm wrote:
> On Tue, Sep 15, 2020 at 14:14:30 +0100, Grant Likely wrote:
>>> The EFI stub in Linux removes /memreserve/ entries from the DT
>>> before
>>> handing it to the kernel proper.
>>>
>>> commit 0ceac9e094b065fe3fec19669740f338d3480498
>>> Author: Mark Salter 
>>> Date:   Mon Sep 8 13:01:08 2014 -0400
>>>
>>>   efi/arm64: Fix fdt-related memory reservation
>>
>> Does that still make sense? I understand why it was done, but is it
>> right to ignore those reservations outright?
>
> Yes. It is duplication of (sources of) information, forcing the
> operating system to make runtime, or compile time, judgement calls of
> which source(s) of information to respect.

 Not quite that simple. We're not talking about a clean cut-over from
 non-UEFI to UEFI platforms, but rather a phased transition where with a
 given DT, both the non-UEFI and UEFI boot paths need to work. e.g.,
 U-Boot platforms where most people are using 'bootm', but want to start
 encouraging them to use the UEFI infrastructure.

 Or in other words, the master source of information is the .dts file,
 not the firmware itself.

 The other issue is that the reserved memory region may not be about
 firmware at all, but rather a memory layout that is wanted only by the
 OS. Regardless of the approach we take here, those regions must be
 respected.

>> As more U-Boot platforms
>> turn on UEFI there could be unexpected consequences if the memory
>> reservation block are silently ignored. I'm think that on the U-Boot
>> platforms it is more likely that /memreserve/ is in use.
>
> That should also make it easy to intercept? Like putting a hook in the
> DT update code that triggers build error/warning (or even update the
> UEFI memory map) if someone is trying to memreserve with the UEFI
> interface enabled.

 It should not be an error to use /memreserve/. That creates a hard
 break
 between UEFI and non-UEFI boot paths for /memreserve/. Updating the
 memory map is fine, which leads to the question of what memory type
 should be used?

 EfiBootServicesData: Memory still gets mapped in the linear map, but
 nothing protects it after ExitBootServices (would require leaving
 /memreserve/ intact so the OS knows to protect them).

 EfiReservedMemory: (As I understand it) Doesn't need /memreserve/, but
 causes a change in behaviour. The memory will not appear in the linear
 map. This will possibly cause problems with existing drivers

>>>
>>> I wouldn't expect so. Unlike /reserved-memory nodes, which can be
>>> referenced by other nodes and explicitly tagged as reusable,
>>> /memreserve/s are anonymous holes that are punched into the memory
>>> map, so I don't see how a driver would be able to get a reference to
>>> that memory (and gets its linear address if it _happens_ to be in
>>> lowmem in the first place.)
>>>
 EfiRuntimeServicesData: Keeps the region protected and in the linear
 map, but feels 'wrong'. An OS might decide to reclaim it anyway if it
 doesn't use runtime services (against spec?).

>>>
>>> EfiRuntimeServicesData is not covered by the linear map, but will map
>>> it in the EFI page tables for access by the firmware itself at
>>> runtime, so it is not an option here.
>>
>>
>> The device-tree spec specifically says /mmemreserve/ serve to "define an
>> entry for the devicetree blob’s memory reservation table."
>
> I think this is just poorly worded. It would be better written as:
>     "Memory reservations create entries in the devicetree blob’s
>     memory reservation table."

Shouldn't the description of /memreserve/ refer to chapter 5.3 Memory
Reservation Block? E.g.

"Memory reservations blocks (see chapter 5.3) are represented by lines
of the form

/memreserve/  ;

where  and  are 64-bit C-style integers, e.g.

/memreserve/ 0x1000 0x0004000;"

Some requirements in chapter 5.3.1 sound similar to the description of
the no-map sub-nodes of /reserved-memory, e.g. speculative access is
prohibited:

"Any memory that is declared in a memory node and is accessed by the
boot program or caused to be accessed by the boot program after client
entry must be reserved. Examples of this type of access include (e.g.,
speculative memory reads through a non-guarded virtual page)."

So in line with our discussion concerning no-map EfiReservedMemoryType
seems the most appropriate.

UEFI runtime drivers will be relocated by SetVirtualMemoryMap(). So the
requirement in the above citation does not make much sense for memory
that is EfiRuntimeServicesCode or 

Re: [PATCH 1/1] GetMemoryMap(), handling of no-map DT property

[Grant Likely]

On 15/09/2020 16:31, Leif Lindholm wrote:

On Tue, Sep 15, 2020 at 15:04:44 +0100, Grant Likely wrote:

On 15/09/2020 14:46, Leif Lindholm wrote:
EfiBootServicesData: Memory still gets mapped in the linear map, but
nothing protects it after ExitBootServices (would require leaving
/memreserve/ intact so the OS knows to protect them).

EfiReservedMemory: (As I understand it) Doesn't need /memreserve/, but
causes a change in behaviour. The memory will not appear in the linear
map. This will possibly cause problems with existing drivers

EfiRuntimeServicesData: Keeps the region protected and in the linear
map, but feels 'wrong'. An OS might decide to reclaim it anyway if it
doesn't use runtime services (against spec?).

Other options?


I'll defer to Ard on the actual selection.

But while care should take not to actively *break* Linux (esp wrt
backwards compatibility), if we end up picking one over the other
based only (or mainly) on Linux internals, we need to very clearly
call that out in the spec.


That's certainly my intent. This is undefined behaviour right now, so
Linux behaviour is the de-facto starndard. I'd like to get that coded
into a spec.

g.
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Re: [PATCH 1/1] GetMemoryMap(), handling of no-map DT property

[Leif Lindholm]

On Tue, Sep 15, 2020 at 15:04:44 +0100, Grant Likely wrote:
> On 15/09/2020 14:46, Leif Lindholm wrote:
> > On Tue, Sep 15, 2020 at 14:14:30 +0100, Grant Likely wrote:
> > > > The EFI stub in Linux removes /memreserve/ entries from the DT before
> > > > handing it to the kernel proper.
> > > > 
> > > > commit 0ceac9e094b065fe3fec19669740f338d3480498
> > > > Author: Mark Salter 
> > > > Date:   Mon Sep 8 13:01:08 2014 -0400
> > > > 
> > > >  efi/arm64: Fix fdt-related memory reservation
> > > 
> > > Does that still make sense? I understand why it was done, but is it
> > > right to ignore those reservations outright?
> > 
> > Yes. It is duplication of (sources of) information, forcing the
> > operating system to make runtime, or compile time, judgement calls of
> > which source(s) of information to respect.
> 
> Not quite that simple. We're not talking about a clean cut-over from
> non-UEFI to UEFI platforms, but rather a phased transition where with a
> given DT, both the non-UEFI and UEFI boot paths need to work. e.g.,
> U-Boot platforms where most people are using 'bootm', but want to start
> encouraging them to use the UEFI infrastructure.

Sure. They can keep their reservations in the device tree, but if a
platform boots in UEFI mode, those reservations should be present in
the UEFI memory map. Then linux can keep ignoring the DT reservations
if booted through the EFI stub.

> Or in other words, the master source of information is the .dts file,
> not the firmware itself.

This does not absolve u-boot from doing something sensible with what
it's passed. This would not be the first thing u-boot would be
runtime-processing the DT for.

> The other issue is that the reserved memory region may not be about
> firmware at all, but rather a memory layout that is wanted only by the
> OS. Regardless of the approach we take here, those regions must be
> respected.
> 
> > > As more U-Boot platforms
> > > turn on UEFI there could be unexpected consequences if the memory
> > > reservation block are silently ignored. I'm think that on the U-Boot
> > > platforms it is more likely that /memreserve/ is in use.
> > 
> > That should also make it easy to intercept? Like putting a hook in the
> > DT update code that triggers build error/warning (or even update the
> > UEFI memory map) if someone is trying to memreserve with the UEFI
> > interface enabled.
> 
> It should not be an error to use /memreserve/. That creates a hard break
> between UEFI and non-UEFI boot paths for /memreserve/. Updating the
> memory map is fine, which leads to the question of what memory type
> should be used?
> 
> EfiBootServicesData: Memory still gets mapped in the linear map, but
> nothing protects it after ExitBootServices (would require leaving
> /memreserve/ intact so the OS knows to protect them).
> 
> EfiReservedMemory: (As I understand it) Doesn't need /memreserve/, but
> causes a change in behaviour. The memory will not appear in the linear
> map. This will possibly cause problems with existing drivers
> 
> EfiRuntimeServicesData: Keeps the region protected and in the linear
> map, but feels 'wrong'. An OS might decide to reclaim it anyway if it
> doesn't use runtime services (against spec?).
> 
> Other options?

I'll defer to Ard on the actual selection.

But while care should take not to actively *break* Linux (esp wrt
backwards compatibility), if we end up picking one over the other
based only (or mainly) on Linux internals, we need to very clearly
call that out in the spec.

Regards,

Leif
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Re: [PATCH 1/1] GetMemoryMap(), handling of no-map DT property

[Grant Likely]

On 15/09/2020 15:36, Heinrich Schuchardt wrote:

On 15.09.20 16:16, Ard Biesheuvel wrote:

On Tue, 15 Sep 2020 at 17:05, Grant Likely  wrote:




On 15/09/2020 14:46, Leif Lindholm wrote:

On Tue, Sep 15, 2020 at 14:14:30 +0100, Grant Likely wrote:

The EFI stub in Linux removes /memreserve/ entries from the DT before
handing it to the kernel proper.

commit 0ceac9e094b065fe3fec19669740f338d3480498
Author: Mark Salter 
Date:   Mon Sep 8 13:01:08 2014 -0400

  efi/arm64: Fix fdt-related memory reservation


Does that still make sense? I understand why it was done, but is it
right to ignore those reservations outright?


Yes. It is duplication of (sources of) information, forcing the
operating system to make runtime, or compile time, judgement calls of
which source(s) of information to respect.


Not quite that simple. We're not talking about a clean cut-over from
non-UEFI to UEFI platforms, but rather a phased transition where with a
given DT, both the non-UEFI and UEFI boot paths need to work. e.g.,
U-Boot platforms where most people are using 'bootm', but want to start
encouraging them to use the UEFI infrastructure.

Or in other words, the master source of information is the .dts file,
not the firmware itself.

The other issue is that the reserved memory region may not be about
firmware at all, but rather a memory layout that is wanted only by the
OS. Regardless of the approach we take here, those regions must be
respected.


As more U-Boot platforms
turn on UEFI there could be unexpected consequences if the memory
reservation block are silently ignored. I'm think that on the U-Boot
platforms it is more likely that /memreserve/ is in use.


That should also make it easy to intercept? Like putting a hook in the
DT update code that triggers build error/warning (or even update the
UEFI memory map) if someone is trying to memreserve with the UEFI
interface enabled.


It should not be an error to use /memreserve/. That creates a hard break
between UEFI and non-UEFI boot paths for /memreserve/. Updating the
memory map is fine, which leads to the question of what memory type
should be used?

EfiBootServicesData: Memory still gets mapped in the linear map, but
nothing protects it after ExitBootServices (would require leaving
/memreserve/ intact so the OS knows to protect them).

EfiReservedMemory: (As I understand it) Doesn't need /memreserve/, but
causes a change in behaviour. The memory will not appear in the linear
map. This will possibly cause problems with existing drivers



I wouldn't expect so. Unlike /reserved-memory nodes, which can be
referenced by other nodes and explicitly tagged as reusable,
/memreserve/s are anonymous holes that are punched into the memory
map, so I don't see how a driver would be able to get a reference to
that memory (and gets its linear address if it _happens_ to be in
lowmem in the first place.)


EfiRuntimeServicesData: Keeps the region protected and in the linear
map, but feels 'wrong'. An OS might decide to reclaim it anyway if it
doesn't use runtime services (against spec?).



EfiRuntimeServicesData is not covered by the linear map, but will map
it in the EFI page tables for access by the firmware itself at
runtime, so it is not an option here.



The device-tree spec specifically says /mmemreserve/ serve to "define an
entry for the devicetree blob’s memory reservation table."


I think this is just poorly worded. It would be better written as:
"Memory reservations create entries in the devicetree blob’s
memory reservation table."


If I look at Linux code I find things like:

/* First 4KB has trampoline code for secondary cores. */
/memreserve/ 0x 0x0001000;

/* firmware-provided startup stubs live here, where the secondary CPUs are
  * spinning.
  */
/memreserve/ 0x 0x1000;

/memreserve/ 0x1000 0x0004000;*/  /* DSP RAM */

CPUs with a 'spin-table' enable-method "should spin outside of the
kernel in a reserved area of memory (communicated to the kernel by a
/memreserve/ region in the device tree".

This usage is not what I would have understood under the description in
the devicetree spec. So the DT spec needs some clarification.

The problem with EfiRuntimeServicesData is that it can be moved anywhere
in the virtual address space via SetVirtualAddressMap(). But do we know
that the firmware can handle such a relocation?

Best regards

Heinrich









It should be fine for /memreserve/ entries to get applied to the memmap
during boot. Are there problems that I'm missing?


Sure. They can be applied in the UEFI memory map. By u-boot, during
boot.

/
  Leif


g.
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Re: [PATCH 1/1] GetMemoryMap(), handling of no-map DT property

[Ard Biesheuvel]

On Tue, 15 Sep 2020 at 17:33, Grant Likely  wrote:
>
>
>
> On 15/09/2020 15:16, Ard Biesheuvel wrote:
> > On Tue, 15 Sep 2020 at 17:05, Grant Likely  wrote:
> >>
> >>
> >>
> >> On 15/09/2020 14:46, Leif Lindholm wrote:
> >>> On Tue, Sep 15, 2020 at 14:14:30 +0100, Grant Likely wrote:
> > The EFI stub in Linux removes /memreserve/ entries from the DT before
> > handing it to the kernel proper.
> >
> > commit 0ceac9e094b065fe3fec19669740f338d3480498
> > Author: Mark Salter 
> > Date:   Mon Sep 8 13:01:08 2014 -0400
> >
> >   efi/arm64: Fix fdt-related memory reservation
> 
>  Does that still make sense? I understand why it was done, but is it
>  right to ignore those reservations outright?
> >>>
> >>> Yes. It is duplication of (sources of) information, forcing the
> >>> operating system to make runtime, or compile time, judgement calls of
> >>> which source(s) of information to respect.
> >>
> >> Not quite that simple. We're not talking about a clean cut-over from
> >> non-UEFI to UEFI platforms, but rather a phased transition where with a
> >> given DT, both the non-UEFI and UEFI boot paths need to work. e.g.,
> >> U-Boot platforms where most people are using 'bootm', but want to start
> >> encouraging them to use the UEFI infrastructure.
> >>
> >> Or in other words, the master source of information is the .dts file,
> >> not the firmware itself.
> >>
> >> The other issue is that the reserved memory region may not be about
> >> firmware at all, but rather a memory layout that is wanted only by the
> >> OS. Regardless of the approach we take here, those regions must be
> >> respected.
> >>
>  As more U-Boot platforms
>  turn on UEFI there could be unexpected consequences if the memory
>  reservation block are silently ignored. I'm think that on the U-Boot
>  platforms it is more likely that /memreserve/ is in use.
> >>>
> >>> That should also make it easy to intercept? Like putting a hook in the
> >>> DT update code that triggers build error/warning (or even update the
> >>> UEFI memory map) if someone is trying to memreserve with the UEFI
> >>> interface enabled.
> >>
> >> It should not be an error to use /memreserve/. That creates a hard break
> >> between UEFI and non-UEFI boot paths for /memreserve/. Updating the
> >> memory map is fine, which leads to the question of what memory type
> >> should be used?
> >>
> >> EfiBootServicesData: Memory still gets mapped in the linear map, but
> >> nothing protects it after ExitBootServices (would require leaving
> >> /memreserve/ intact so the OS knows to protect them).
> >>
> >> EfiReservedMemory: (As I understand it) Doesn't need /memreserve/, but
> >> causes a change in behaviour. The memory will not appear in the linear
> >> map. This will possibly cause problems with existing drivers
> >>
> >
> > I wouldn't expect so. Unlike /reserved-memory nodes, which can be
> > referenced by other nodes and explicitly tagged as reusable,
> > /memreserve/s are anonymous holes that are punched into the memory
> > map, so I don't see how a driver would be able to get a reference to
> > that memory (and gets its linear address if it _happens_ to be in
> > lowmem in the first place.)
>
> In the typical use case, the driver doesn't directly use the
> /memreserve/ entry, but rather knowledge of the hole is implicit; the
> driver expects it to exist via some other mechanism. E.g., a property in
> the device node. If /memreserve/ gets cleared out, the device node will
> probably still try to use the region as if it had been reserved.
>
> e.g.:
> powerpc/boot/dts/akebono.dts: <0x1f0 0x10> is reserved, and then
> used in the cpu-release-address property. This is a case where the
> memory should still be in the linear map.
>

That depends on how the boot CPU accesses this memory - a quick scan
shows that many drivers ioremap() this address rather than access it
via the linear mapping.

> These are old use cases, and /memreserve/ is definitely deprecated in
> favour of the /reserved-memory node, but it has users and I absolutely
> do not want to create barriers to adopting the UEFI boot flow.
>
> >> EfiRuntimeServicesData: Keeps the region protected and in the linear
> >> map, but feels 'wrong'. An OS might decide to reclaim it anyway if it
> >> doesn't use runtime services (against spec?).
> >>
> >
> > EfiRuntimeServicesData is not covered by the linear map, but will map
> > it in the EFI page tables for access by the firmware itself at
> > runtime, so it is not an option here.
>
> Ah, right. So that isn't right either.
>
> g.
>
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> recipient, please notify the sender immediately and do not disclose the 
> contents to any other person, use it for any purpose, or store or copy the 
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Re: [PATCH 1/1] GetMemoryMap(), handling of no-map DT property

[Heinrich Schuchardt]

On 15.09.20 16:16, Ard Biesheuvel wrote:
> On Tue, 15 Sep 2020 at 17:05, Grant Likely  wrote:
>>
>>
>>
>> On 15/09/2020 14:46, Leif Lindholm wrote:
>>> On Tue, Sep 15, 2020 at 14:14:30 +0100, Grant Likely wrote:
> The EFI stub in Linux removes /memreserve/ entries from the DT before
> handing it to the kernel proper.
>
> commit 0ceac9e094b065fe3fec19669740f338d3480498
> Author: Mark Salter 
> Date:   Mon Sep 8 13:01:08 2014 -0400
>
>  efi/arm64: Fix fdt-related memory reservation

 Does that still make sense? I understand why it was done, but is it
 right to ignore those reservations outright?
>>>
>>> Yes. It is duplication of (sources of) information, forcing the
>>> operating system to make runtime, or compile time, judgement calls of
>>> which source(s) of information to respect.
>>
>> Not quite that simple. We're not talking about a clean cut-over from
>> non-UEFI to UEFI platforms, but rather a phased transition where with a
>> given DT, both the non-UEFI and UEFI boot paths need to work. e.g.,
>> U-Boot platforms where most people are using 'bootm', but want to start
>> encouraging them to use the UEFI infrastructure.
>>
>> Or in other words, the master source of information is the .dts file,
>> not the firmware itself.
>>
>> The other issue is that the reserved memory region may not be about
>> firmware at all, but rather a memory layout that is wanted only by the
>> OS. Regardless of the approach we take here, those regions must be
>> respected.
>>
 As more U-Boot platforms
 turn on UEFI there could be unexpected consequences if the memory
 reservation block are silently ignored. I'm think that on the U-Boot
 platforms it is more likely that /memreserve/ is in use.
>>>
>>> That should also make it easy to intercept? Like putting a hook in the
>>> DT update code that triggers build error/warning (or even update the
>>> UEFI memory map) if someone is trying to memreserve with the UEFI
>>> interface enabled.
>>
>> It should not be an error to use /memreserve/. That creates a hard break
>> between UEFI and non-UEFI boot paths for /memreserve/. Updating the
>> memory map is fine, which leads to the question of what memory type
>> should be used?
>>
>> EfiBootServicesData: Memory still gets mapped in the linear map, but
>> nothing protects it after ExitBootServices (would require leaving
>> /memreserve/ intact so the OS knows to protect them).
>>
>> EfiReservedMemory: (As I understand it) Doesn't need /memreserve/, but
>> causes a change in behaviour. The memory will not appear in the linear
>> map. This will possibly cause problems with existing drivers
>>
>
> I wouldn't expect so. Unlike /reserved-memory nodes, which can be
> referenced by other nodes and explicitly tagged as reusable,
> /memreserve/s are anonymous holes that are punched into the memory
> map, so I don't see how a driver would be able to get a reference to
> that memory (and gets its linear address if it _happens_ to be in
> lowmem in the first place.)
>
>> EfiRuntimeServicesData: Keeps the region protected and in the linear
>> map, but feels 'wrong'. An OS might decide to reclaim it anyway if it
>> doesn't use runtime services (against spec?).
>>
>
> EfiRuntimeServicesData is not covered by the linear map, but will map
> it in the EFI page tables for access by the firmware itself at
> runtime, so it is not an option here.


The device-tree spec specifically says /mmemreserve/ serve to "define an
entry for the devicetree blob’s memory reservation table."

If I look at Linux code I find things like:

/* First 4KB has trampoline code for secondary cores. */
/memreserve/ 0x 0x0001000;

/* firmware-provided startup stubs live here, where the secondary CPUs are
 * spinning.
 */
/memreserve/ 0x 0x1000;

/memreserve/ 0x1000 0x0004000;*/  /* DSP RAM */

CPUs with a 'spin-table' enable-method "should spin outside of the
kernel in a reserved area of memory (communicated to the kernel by a
/memreserve/ region in the device tree".

This usage is not what I would have understood under the description in
the devicetree spec. So the DT spec needs some clarification.

The problem with EfiRuntimeServicesData is that it can be moved anywhere
in the virtual address space via SetVirtualAddressMap(). But do we know
that the firmware can handle such a relocation?

Best regards

Heinrich

>
>
>>
>>>
 It should be fine for /memreserve/ entries to get applied to the memmap
 during boot. Are there problems that I'm missing?
>>>
>>> Sure. They can be applied in the UEFI memory map. By u-boot, during
>>> boot.
>>>
>>> /
>>>  Leif
>>>
 g.
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 contents to any other person, use it for any purpose, or store or copy the 
 information in 

Re: [PATCH 1/1] GetMemoryMap(), handling of no-map DT property

[Ard Biesheuvel]

On Tue, 15 Sep 2020 at 17:05, Grant Likely  wrote:
>
>
>
> On 15/09/2020 14:46, Leif Lindholm wrote:
> > On Tue, Sep 15, 2020 at 14:14:30 +0100, Grant Likely wrote:
> >>> The EFI stub in Linux removes /memreserve/ entries from the DT before
> >>> handing it to the kernel proper.
> >>>
> >>> commit 0ceac9e094b065fe3fec19669740f338d3480498
> >>> Author: Mark Salter 
> >>> Date:   Mon Sep 8 13:01:08 2014 -0400
> >>>
> >>>  efi/arm64: Fix fdt-related memory reservation
> >>
> >> Does that still make sense? I understand why it was done, but is it
> >> right to ignore those reservations outright?
> >
> > Yes. It is duplication of (sources of) information, forcing the
> > operating system to make runtime, or compile time, judgement calls of
> > which source(s) of information to respect.
>
> Not quite that simple. We're not talking about a clean cut-over from
> non-UEFI to UEFI platforms, but rather a phased transition where with a
> given DT, both the non-UEFI and UEFI boot paths need to work. e.g.,
> U-Boot platforms where most people are using 'bootm', but want to start
> encouraging them to use the UEFI infrastructure.
>
> Or in other words, the master source of information is the .dts file,
> not the firmware itself.
>
> The other issue is that the reserved memory region may not be about
> firmware at all, but rather a memory layout that is wanted only by the
> OS. Regardless of the approach we take here, those regions must be
> respected.
>
> >> As more U-Boot platforms
> >> turn on UEFI there could be unexpected consequences if the memory
> >> reservation block are silently ignored. I'm think that on the U-Boot
> >> platforms it is more likely that /memreserve/ is in use.
> >
> > That should also make it easy to intercept? Like putting a hook in the
> > DT update code that triggers build error/warning (or even update the
> > UEFI memory map) if someone is trying to memreserve with the UEFI
> > interface enabled.
>
> It should not be an error to use /memreserve/. That creates a hard break
> between UEFI and non-UEFI boot paths for /memreserve/. Updating the
> memory map is fine, which leads to the question of what memory type
> should be used?
>
> EfiBootServicesData: Memory still gets mapped in the linear map, but
> nothing protects it after ExitBootServices (would require leaving
> /memreserve/ intact so the OS knows to protect them).
>
> EfiReservedMemory: (As I understand it) Doesn't need /memreserve/, but
> causes a change in behaviour. The memory will not appear in the linear
> map. This will possibly cause problems with existing drivers
>

I wouldn't expect so. Unlike /reserved-memory nodes, which can be
referenced by other nodes and explicitly tagged as reusable,
/memreserve/s are anonymous holes that are punched into the memory
map, so I don't see how a driver would be able to get a reference to
that memory (and gets its linear address if it _happens_ to be in
lowmem in the first place.)

> EfiRuntimeServicesData: Keeps the region protected and in the linear
> map, but feels 'wrong'. An OS might decide to reclaim it anyway if it
> doesn't use runtime services (against spec?).
>

EfiRuntimeServicesData is not covered by the linear map, but will map
it in the EFI page tables for access by the firmware itself at
runtime, so it is not an option here.


>
> >
> >> It should be fine for /memreserve/ entries to get applied to the memmap
> >> during boot. Are there problems that I'm missing?
> >
> > Sure. They can be applied in the UEFI memory map. By u-boot, during
> > boot.
> >
> > /
> >  Leif
> >
> >> g.
> >> IMPORTANT NOTICE: The contents of this email and any attachments are 
> >> confidential and may also be privileged. If you are not the intended 
> >> recipient, please notify the sender immediately and do not disclose the 
> >> contents to any other person, use it for any purpose, or store or copy the 
> >> information in any medium. Thank you.
> >> ___
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> >> boot-architecture@lists.linaro.org
> >> https://lists.linaro.org/mailman/listinfo/boot-architecture
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Re: [PATCH 1/1] GetMemoryMap(), handling of no-map DT property

[Grant Likely]

On 15/09/2020 14:59, Heinrich Schuchardt wrote:

On 15.09.20 15:46, Leif Lindholm wrote:

On Tue, Sep 15, 2020 at 14:14:30 +0100, Grant Likely wrote:

+``/memory`` node and UEFI
+~~
+
+When booting via [UEFI]_, the system memory map is obtained via the
+GetMemoryMap() UEFI boot time service as defined in [UEFI]_ § 7.2,
+and if present, the OS must ignore any ``/memory`` nodes.



This should cover /memreserve/ entries as well.


What memory type should be used for /memreserve/? The memory reserve
block isn't nearly as expressive, so we don't have details about how to
use it. Be conservative and specify EfiReservedMemoryType?



Currently, we simply ignore memreserve's like we ignore the memory
nodes as well.


Looks like in Linux the memory is reserved without the nomap behaviour
(not removed). Unlike with /reserved-memory, EfiBootServicesData won't
currently give us the behaviour we want if the kernel is currently
ignoring the memory reserved block. (for /reserved-memory, the kernel
'finds' the reservations again during early boot, so the UEFI
protections only need to extend to the ExitBootServices() call. With the
memory reserved block, the kernel has no way to know if it should
continue to respect those reservations after ExitBootServices if it
isn't parsing the block.

Should the kernel still respect Memory Reserved block when booting via
UEFI? At this point I'm inclined to say yes.



The EFI stub in Linux removes /memreserve/ entries from the DT before
handing it to the kernel proper.

commit 0ceac9e094b065fe3fec19669740f338d3480498
Author: Mark Salter 
Date:   Mon Sep 8 13:01:08 2014 -0400

 efi/arm64: Fix fdt-related memory reservation


Does that still make sense? I understand why it was done, but is it
right to ignore those reservations outright?


Yes. It is duplication of (sources of) information, forcing the
operating system to make runtime, or compile time, judgement calls of
which source(s) of information to respect.


As more U-Boot platforms
turn on UEFI there could be unexpected consequences if the memory
reservation block are silently ignored. I'm think that on the U-Boot
platforms it is more likely that /memreserve/ is in use.


That should also make it easy to intercept? Like putting a hook in the
DT update code that triggers build error/warning (or even update the
UEFI memory map) if someone is trying to memreserve with the UEFI
interface enabled.


It should be fine for /memreserve/ entries to get applied to the memmap
during boot. Are there problems that I'm missing?


Sure. They can be applied in the UEFI memory map. By u-boot, during
boot.

The device-tree spec says they are used for device tree blobs. So I
guess in the memory map returned by GetMemoryMap() they would have to be
EfiACPIReclaimMemory like the area for the device-tree itself. We should
define this in the EBBR.


What bit is that? I see the text saying /memreserve/ adds an entry to
the blob's reservation table, but not that it is used for device tree blobs:

   Memory reservations define an entry for the devicetree blob’s memory
   reservation table. They have the form: e.g., /memreserve/ 
   ; Where  and  are 64-bit C-style integers.

g.



In the device-tree spec an example showing the syntax of /memreserve/
nodes should be added.

Best regards

Heinrich



/
 Leif


g.
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Re: [PATCH 1/1] GetMemoryMap(), handling of no-map DT property

[Grant Likely]

On 15/09/2020 14:46, Leif Lindholm wrote:

On Tue, Sep 15, 2020 at 14:14:30 +0100, Grant Likely wrote:

The EFI stub in Linux removes /memreserve/ entries from the DT before
handing it to the kernel proper.

commit 0ceac9e094b065fe3fec19669740f338d3480498
Author: Mark Salter 
Date:   Mon Sep 8 13:01:08 2014 -0400

 efi/arm64: Fix fdt-related memory reservation


Does that still make sense? I understand why it was done, but is it
right to ignore those reservations outright?


Yes. It is duplication of (sources of) information, forcing the
operating system to make runtime, or compile time, judgement calls of
which source(s) of information to respect.


Not quite that simple. We're not talking about a clean cut-over from
non-UEFI to UEFI platforms, but rather a phased transition where with a
given DT, both the non-UEFI and UEFI boot paths need to work. e.g.,
U-Boot platforms where most people are using 'bootm', but want to start
encouraging them to use the UEFI infrastructure.

Or in other words, the master source of information is the .dts file,
not the firmware itself.

The other issue is that the reserved memory region may not be about
firmware at all, but rather a memory layout that is wanted only by the
OS. Regardless of the approach we take here, those regions must be
respected.


As more U-Boot platforms
turn on UEFI there could be unexpected consequences if the memory
reservation block are silently ignored. I'm think that on the U-Boot
platforms it is more likely that /memreserve/ is in use.


That should also make it easy to intercept? Like putting a hook in the
DT update code that triggers build error/warning (or even update the
UEFI memory map) if someone is trying to memreserve with the UEFI
interface enabled.


It should not be an error to use /memreserve/. That creates a hard break
between UEFI and non-UEFI boot paths for /memreserve/. Updating the
memory map is fine, which leads to the question of what memory type
should be used?

EfiBootServicesData: Memory still gets mapped in the linear map, but
nothing protects it after ExitBootServices (would require leaving
/memreserve/ intact so the OS knows to protect them).

EfiReservedMemory: (As I understand it) Doesn't need /memreserve/, but
causes a change in behaviour. The memory will not appear in the linear
map. This will possibly cause problems with existing drivers

EfiRuntimeServicesData: Keeps the region protected and in the linear
map, but feels 'wrong'. An OS might decide to reclaim it anyway if it
doesn't use runtime services (against spec?).

Other options?




It should be fine for /memreserve/ entries to get applied to the memmap
during boot. Are there problems that I'm missing?


Sure. They can be applied in the UEFI memory map. By u-boot, during
boot.

/
 Leif


g.
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Re: [PATCH 1/1] GetMemoryMap(), handling of no-map DT property

[Heinrich Schuchardt]

On 15.09.20 15:46, Leif Lindholm wrote:
> On Tue, Sep 15, 2020 at 14:14:30 +0100, Grant Likely wrote:
 +``/memory`` node and UEFI
 +~~
 +
 +When booting via [UEFI]_, the system memory map is obtained via the
 +GetMemoryMap() UEFI boot time service as defined in [UEFI]_ § 7.2,
 +and if present, the OS must ignore any ``/memory`` nodes.

>>>
>>> This should cover /memreserve/ entries as well.
>>
>> What memory type should be used for /memreserve/? The memory reserve
>> block isn't nearly as expressive, so we don't have details about how to
>> use it. Be conservative and specify EfiReservedMemoryType?
>>
>
> Currently, we simply ignore memreserve's like we ignore the memory
> nodes as well.

 Looks like in Linux the memory is reserved without the nomap behaviour
 (not removed). Unlike with /reserved-memory, EfiBootServicesData won't
 currently give us the behaviour we want if the kernel is currently
 ignoring the memory reserved block. (for /reserved-memory, the kernel
 'finds' the reservations again during early boot, so the UEFI
 protections only need to extend to the ExitBootServices() call. With the
 memory reserved block, the kernel has no way to know if it should
 continue to respect those reservations after ExitBootServices if it
 isn't parsing the block.

 Should the kernel still respect Memory Reserved block when booting via
 UEFI? At this point I'm inclined to say yes.

>>>
>>> The EFI stub in Linux removes /memreserve/ entries from the DT before
>>> handing it to the kernel proper.
>>>
>>> commit 0ceac9e094b065fe3fec19669740f338d3480498
>>> Author: Mark Salter 
>>> Date:   Mon Sep 8 13:01:08 2014 -0400
>>>
>>> efi/arm64: Fix fdt-related memory reservation
>>
>> Does that still make sense? I understand why it was done, but is it
>> right to ignore those reservations outright?
>
> Yes. It is duplication of (sources of) information, forcing the
> operating system to make runtime, or compile time, judgement calls of
> which source(s) of information to respect.
>
>> As more U-Boot platforms
>> turn on UEFI there could be unexpected consequences if the memory
>> reservation block are silently ignored. I'm think that on the U-Boot
>> platforms it is more likely that /memreserve/ is in use.
>
> That should also make it easy to intercept? Like putting a hook in the
> DT update code that triggers build error/warning (or even update the
> UEFI memory map) if someone is trying to memreserve with the UEFI
> interface enabled.
>
>> It should be fine for /memreserve/ entries to get applied to the memmap
>> during boot. Are there problems that I'm missing?
>
> Sure. They can be applied in the UEFI memory map. By u-boot, during
> boot.
The device-tree spec says they are used for device tree blobs. So I
guess in the memory map returned by GetMemoryMap() they would have to be
EfiACPIReclaimMemory like the area for the device-tree itself. We should
define this in the EBBR.

In the device-tree spec an example showing the syntax of /memreserve/
nodes should be added.

Best regards

Heinrich

>
> /
> Leif
>
>> g.
>> IMPORTANT NOTICE: The contents of this email and any attachments are 
>> confidential and may also be privileged. If you are not the intended 
>> recipient, please notify the sender immediately and do not disclose the 
>> contents to any other person, use it for any purpose, or store or copy the 
>> information in any medium. Thank you.
>> ___
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>> boot-architecture@lists.linaro.org
>> https://lists.linaro.org/mailman/listinfo/boot-architecture

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Re: [PATCH 1/1] GetMemoryMap(), handling of no-map DT property

[Ard Biesheuvel]

On Tue, 15 Sep 2020 at 16:15, Grant Likely  wrote:
>
> On 15/09/2020 14:02, Ard Biesheuvel wrote:
> > On Tue, 15 Sep 2020 at 15:59, Grant Likely  wrote:
> >>
> >>
> >>
> >> On 15/09/2020 13:35, Ard Biesheuvel wrote:
> >>> On Tue, 15 Sep 2020 at 15:34, Grant Likely  wrote:
> 
> 
> 
>  On 15/09/2020 13:25, Ard Biesheuvel wrote:
> > On Tue, 15 Sep 2020 at 15:22, Grant Likely  wrote:
> >>
> >> On 15/09/2020 09:33, Heinrich Schuchardt wrote:
> >>> Closes: #52
> >>>
> >>> The no-map property of the /reserved-memory device tree nodes is used 
> >>> to
> >>> signal that a memory region shall not be accessed by the operating 
> >>> system,
> >>> even not via speculative access.
> >>>
> >>> /reserved-memory nodes without the no-map property describe memory 
> >>> that
> >>> have special usage by the operating system.
> >>>
> >>> This difference has to be reflected in the memory map returned by
> >>> GetMemoryMap().
> >>>
> >>> Signed-off-by: Heinrich Schuchardt 
> >>> ---
> >>>  source/chapter2-uefi.rst | 13 +
> >>>  source/references.rst|  4 
> >>>  2 files changed, 17 insertions(+)
> >>>
> >>> diff --git a/source/chapter2-uefi.rst b/source/chapter2-uefi.rst
> >>> index 74ef70e..f410c57 100644
> >>> --- a/source/chapter2-uefi.rst
> >>> +++ b/source/chapter2-uefi.rst
> >>> @@ -74,6 +74,19 @@ that virtual addresses must equal physical 
> >>> addresses.
> >>>
> >>>  The default RAM allocated attribute must be EFI_MEMORY_WB.
> >>>
> >>> +In the device tree reserved memory in modelled as a /reserved-memory 
> >>> nodes
> >>> +[RESMEM]_. The reserved-memory node MAY carry either the no-map or 
> >>> the resue
> >>> +property. It MUST NOT carry both properties as this would be 
> >>> contradictary.
> >>> +
> >> After having looked at reserved-memory.txt in the kernel and the
> >> devicetree spec, I think this should just go straight into dtspec or
> >> into the kernel tree. I drafted a couple patches yesterday that first
> >> imports /reserved-memory into dtspec, and then adds the UEFI
> >> annotations. Here's the current patch for the latter:
> >>
> >> 
> >>
> >> diff --git a/source/chapter3-devicenodes.rst
> >> b/source/chapter3-devicenodes.rst
> >> index 3043b8a..647e487 100644
> >> --- a/source/chapter3-devicenodes.rst
> >> +++ b/source/chapter3-devicenodes.rst
> >> @@ -160,6 +160,12 @@ If the VLE storage attribute is supported, with 
> >> VLE=0.
> >>  .. note:: All other standard properties (section
> >> :ref:`sect-standard-properties`) are allowed but are optional.
> >>
> >> +``/memory`` node and UEFI
> >> +~~
> >> +
> >> +When booting via [UEFI]_, the system memory map is obtained via the
> >> +GetMemoryMap() UEFI boot time service as defined in [UEFI]_ § 7.2,
> >> +and if present, the OS must ignore any ``/memory`` nodes.
> >>
> >
> > This should cover /memreserve/ entries as well.
> 
>  What memory type should be used for /memreserve/? The memory reserve
>  block isn't nearly as expressive, so we don't have details about how to
>  use it. Be conservative and specify EfiReservedMemoryType?
> 
> >>>
> >>> Currently, we simply ignore memreserve's like we ignore the memory
> >>> nodes as well.
> >>
> >> Looks like in Linux the memory is reserved without the nomap behaviour
> >> (not removed). Unlike with /reserved-memory, EfiBootServicesData won't
> >> currently give us the behaviour we want if the kernel is currently
> >> ignoring the memory reserved block. (for /reserved-memory, the kernel
> >> 'finds' the reservations again during early boot, so the UEFI
> >> protections only need to extend to the ExitBootServices() call. With the
> >> memory reserved block, the kernel has no way to know if it should
> >> continue to respect those reservations after ExitBootServices if it
> >> isn't parsing the block.
> >>
> >> Should the kernel still respect Memory Reserved block when booting via
> >> UEFI? At this point I'm inclined to say yes.
> >>
> >
> > The EFI stub in Linux removes /memreserve/ entries from the DT before
> > handing it to the kernel proper.
> >
> > commit 0ceac9e094b065fe3fec19669740f338d3480498
> > Author: Mark Salter 
> > Date:   Mon Sep 8 13:01:08 2014 -0400
> >
> > efi/arm64: Fix fdt-related memory reservation
>
> Does that still make sense? I understand why it was done, but is it
> right to ignore those reservations outright? As more U-Boot platforms
> turn on UEFI there could be unexpected consequences if the memory
> reservation block are silently ignored. I'm think that on the U-Boot
> platforms it is more likely that /memreserve/ is in use.
>
> It should be fine for /memreserve/ entries to get applied to the memmap
> 

Re: [PATCH 1/1] GetMemoryMap(), handling of no-map DT property

[Leif Lindholm]

On Tue, Sep 15, 2020 at 14:14:30 +0100, Grant Likely wrote:
> > > > > > > +``/memory`` node and UEFI
> > > > > > > +~~
> > > > > > > +
> > > > > > > +When booting via [UEFI]_, the system memory map is obtained via 
> > > > > > > the
> > > > > > > +GetMemoryMap() UEFI boot time service as defined in [UEFI]_ § 
> > > > > > > 7.2,
> > > > > > > +and if present, the OS must ignore any ``/memory`` nodes.
> > > > > > > 
> > > > > > 
> > > > > > This should cover /memreserve/ entries as well.
> > > > > 
> > > > > What memory type should be used for /memreserve/? The memory reserve
> > > > > block isn't nearly as expressive, so we don't have details about how 
> > > > > to
> > > > > use it. Be conservative and specify EfiReservedMemoryType?
> > > > > 
> > > > 
> > > > Currently, we simply ignore memreserve's like we ignore the memory
> > > > nodes as well.
> > > 
> > > Looks like in Linux the memory is reserved without the nomap behaviour
> > > (not removed). Unlike with /reserved-memory, EfiBootServicesData won't
> > > currently give us the behaviour we want if the kernel is currently
> > > ignoring the memory reserved block. (for /reserved-memory, the kernel
> > > 'finds' the reservations again during early boot, so the UEFI
> > > protections only need to extend to the ExitBootServices() call. With the
> > > memory reserved block, the kernel has no way to know if it should
> > > continue to respect those reservations after ExitBootServices if it
> > > isn't parsing the block.
> > > 
> > > Should the kernel still respect Memory Reserved block when booting via
> > > UEFI? At this point I'm inclined to say yes.
> > > 
> > 
> > The EFI stub in Linux removes /memreserve/ entries from the DT before
> > handing it to the kernel proper.
> > 
> > commit 0ceac9e094b065fe3fec19669740f338d3480498
> > Author: Mark Salter 
> > Date:   Mon Sep 8 13:01:08 2014 -0400
> > 
> > efi/arm64: Fix fdt-related memory reservation
> 
> Does that still make sense? I understand why it was done, but is it
> right to ignore those reservations outright?

Yes. It is duplication of (sources of) information, forcing the
operating system to make runtime, or compile time, judgement calls of
which source(s) of information to respect.

> As more U-Boot platforms
> turn on UEFI there could be unexpected consequences if the memory
> reservation block are silently ignored. I'm think that on the U-Boot
> platforms it is more likely that /memreserve/ is in use.

That should also make it easy to intercept? Like putting a hook in the
DT update code that triggers build error/warning (or even update the
UEFI memory map) if someone is trying to memreserve with the UEFI
interface enabled.

> It should be fine for /memreserve/ entries to get applied to the memmap
> during boot. Are there problems that I'm missing?

Sure. They can be applied in the UEFI memory map. By u-boot, during
boot.

/
Leif

> g.
> IMPORTANT NOTICE: The contents of this email and any attachments are 
> confidential and may also be privileged. If you are not the intended 
> recipient, please notify the sender immediately and do not disclose the 
> contents to any other person, use it for any purpose, or store or copy the 
> information in any medium. Thank you.
> ___
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Re: [PATCH 1/1] GetMemoryMap(), handling of no-map DT property

[Ard Biesheuvel]

On Tue, 15 Sep 2020 at 15:59, Grant Likely  wrote:
>
>
>
> On 15/09/2020 13:35, Ard Biesheuvel wrote:
> > On Tue, 15 Sep 2020 at 15:34, Grant Likely  wrote:
> >>
> >>
> >>
> >> On 15/09/2020 13:25, Ard Biesheuvel wrote:
> >>> On Tue, 15 Sep 2020 at 15:22, Grant Likely  wrote:
> 
>  On 15/09/2020 09:33, Heinrich Schuchardt wrote:
> > Closes: #52
> >
> > The no-map property of the /reserved-memory device tree nodes is used to
> > signal that a memory region shall not be accessed by the operating 
> > system,
> > even not via speculative access.
> >
> > /reserved-memory nodes without the no-map property describe memory that
> > have special usage by the operating system.
> >
> > This difference has to be reflected in the memory map returned by
> > GetMemoryMap().
> >
> > Signed-off-by: Heinrich Schuchardt 
> > ---
> > source/chapter2-uefi.rst | 13 +
> > source/references.rst|  4 
> > 2 files changed, 17 insertions(+)
> >
> > diff --git a/source/chapter2-uefi.rst b/source/chapter2-uefi.rst
> > index 74ef70e..f410c57 100644
> > --- a/source/chapter2-uefi.rst
> > +++ b/source/chapter2-uefi.rst
> > @@ -74,6 +74,19 @@ that virtual addresses must equal physical addresses.
> >
> > The default RAM allocated attribute must be EFI_MEMORY_WB.
> >
> > +In the device tree reserved memory in modelled as a /reserved-memory 
> > nodes
> > +[RESMEM]_. The reserved-memory node MAY carry either the no-map or the 
> > resue
> > +property. It MUST NOT carry both properties as this would be 
> > contradictary.
> > +
>  After having looked at reserved-memory.txt in the kernel and the
>  devicetree spec, I think this should just go straight into dtspec or
>  into the kernel tree. I drafted a couple patches yesterday that first
>  imports /reserved-memory into dtspec, and then adds the UEFI
>  annotations. Here's the current patch for the latter:
> 
>  
> 
>  diff --git a/source/chapter3-devicenodes.rst
>  b/source/chapter3-devicenodes.rst
>  index 3043b8a..647e487 100644
>  --- a/source/chapter3-devicenodes.rst
>  +++ b/source/chapter3-devicenodes.rst
>  @@ -160,6 +160,12 @@ If the VLE storage attribute is supported, with 
>  VLE=0.
>  .. note:: All other standard properties (section
> :ref:`sect-standard-properties`) are allowed but are optional.
> 
>  +``/memory`` node and UEFI
>  +~~
>  +
>  +When booting via [UEFI]_, the system memory map is obtained via the
>  +GetMemoryMap() UEFI boot time service as defined in [UEFI]_ § 7.2,
>  +and if present, the OS must ignore any ``/memory`` nodes.
> 
> >>>
> >>> This should cover /memreserve/ entries as well.
> >>
> >> What memory type should be used for /memreserve/? The memory reserve
> >> block isn't nearly as expressive, so we don't have details about how to
> >> use it. Be conservative and specify EfiReservedMemoryType?
> >>
> >
> > Currently, we simply ignore memreserve's like we ignore the memory
> > nodes as well.
>
> Looks like in Linux the memory is reserved without the nomap behaviour
> (not removed). Unlike with /reserved-memory, EfiBootServicesData won't
> currently give us the behaviour we want if the kernel is currently
> ignoring the memory reserved block. (for /reserved-memory, the kernel
> 'finds' the reservations again during early boot, so the UEFI
> protections only need to extend to the ExitBootServices() call. With the
> memory reserved block, the kernel has no way to know if it should
> continue to respect those reservations after ExitBootServices if it
> isn't parsing the block.
>
> Should the kernel still respect Memory Reserved block when booting via
> UEFI? At this point I'm inclined to say yes.
>

The EFI stub in Linux removes /memreserve/ entries from the DT before
handing it to the kernel proper.

commit 0ceac9e094b065fe3fec19669740f338d3480498
Author: Mark Salter 
Date:   Mon Sep 8 13:01:08 2014 -0400

   efi/arm64: Fix fdt-related memory reservation
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Re: [PATCH 1/1] GetMemoryMap(), handling of no-map DT property

[Ard Biesheuvel]

On Tue, 15 Sep 2020 at 15:34, Grant Likely  wrote:
>
>
>
> On 15/09/2020 13:25, Ard Biesheuvel wrote:
> > On Tue, 15 Sep 2020 at 15:22, Grant Likely  wrote:
> >>
> >> On 15/09/2020 09:33, Heinrich Schuchardt wrote:
> >>> Closes: #52
> >>>
> >>> The no-map property of the /reserved-memory device tree nodes is used to
> >>> signal that a memory region shall not be accessed by the operating system,
> >>> even not via speculative access.
> >>>
> >>> /reserved-memory nodes without the no-map property describe memory that
> >>> have special usage by the operating system.
> >>>
> >>> This difference has to be reflected in the memory map returned by
> >>> GetMemoryMap().
> >>>
> >>> Signed-off-by: Heinrich Schuchardt 
> >>> ---
> >>>source/chapter2-uefi.rst | 13 +
> >>>source/references.rst|  4 
> >>>2 files changed, 17 insertions(+)
> >>>
> >>> diff --git a/source/chapter2-uefi.rst b/source/chapter2-uefi.rst
> >>> index 74ef70e..f410c57 100644
> >>> --- a/source/chapter2-uefi.rst
> >>> +++ b/source/chapter2-uefi.rst
> >>> @@ -74,6 +74,19 @@ that virtual addresses must equal physical addresses.
> >>>
> >>>The default RAM allocated attribute must be EFI_MEMORY_WB.
> >>>
> >>> +In the device tree reserved memory in modelled as a /reserved-memory 
> >>> nodes
> >>> +[RESMEM]_. The reserved-memory node MAY carry either the no-map or the 
> >>> resue
> >>> +property. It MUST NOT carry both properties as this would be 
> >>> contradictary.
> >>> +
> >> After having looked at reserved-memory.txt in the kernel and the
> >> devicetree spec, I think this should just go straight into dtspec or
> >> into the kernel tree. I drafted a couple patches yesterday that first
> >> imports /reserved-memory into dtspec, and then adds the UEFI
> >> annotations. Here's the current patch for the latter:
> >>
> >> 
> >>
> >> diff --git a/source/chapter3-devicenodes.rst
> >> b/source/chapter3-devicenodes.rst
> >> index 3043b8a..647e487 100644
> >> --- a/source/chapter3-devicenodes.rst
> >> +++ b/source/chapter3-devicenodes.rst
> >> @@ -160,6 +160,12 @@ If the VLE storage attribute is supported, with VLE=0.
> >>.. note:: All other standard properties (section
> >>   :ref:`sect-standard-properties`) are allowed but are optional.
> >>
> >> +``/memory`` node and UEFI
> >> +~~
> >> +
> >> +When booting via [UEFI]_, the system memory map is obtained via the
> >> +GetMemoryMap() UEFI boot time service as defined in [UEFI]_ § 7.2,
> >> +and if present, the OS must ignore any ``/memory`` nodes.
> >>
> >
> > This should cover /memreserve/ entries as well.
>
> What memory type should be used for /memreserve/? The memory reserve
> block isn't nearly as expressive, so we don't have details about how to
> use it. Be conservative and specify EfiReservedMemoryType?
>

Currently, we simply ignore memreserve's like we ignore the memory
nodes as well.


>
> >
> >>``/memory`` Examples
> >>
> >> @@ -314,6 +320,9 @@ is ignored.
> >>The ``no-map`` and ``reusable`` properties are mutually exclusive and
> >> both must
> >>not be used together in the same node.
> >>
> >> +Dynamic reserved memory regions must not listed in the [UEFI]_ memory map
> >
> > not be listed
> >
> >> +because they are allocated by the OS after exiting firmware boot services.
> >> +
> >>Linux implementation notes:
> >>
> >>- If a ``linux,cma-default`` property is present, then Linux will use 
> >> the
> >> @@ -341,6 +350,19 @@ nodes by adding a ``memory-region`` property to the
> >> device node.
> >>   Usage legend: R=Required, O=Optional, OR=Optional but Recommended,
> >> SD=See Definition
> >>
> >> ===
> >>
> >> +``/reserved-memory`` and UEFI
> >> +~
> >> +When booting via [UEFI]_, static ``/reserved-memory`` regions must
> >> +also be listed in the system memory map obtained via the GetMemoryMap()
> >> +UEFI boot time service as defined in [UEFI]_ § 7.2.
> >> +The reserved memory regions need to be included in the UEFI memory map to
> >> +protect them from memory allocations by UEFI applications.
> >> +
> >> +Reserved regions with the ``no-map`` property must be listed in the memory
> >> +map with type ``EfiReservedMemoryType``.
> >> +All other reserved regions must be listed with the type
> >> +``EfiBootServicesData``.
> >> +
> >>``/reserved-memory`` Example
> >>
> >>
> >> diff --git a/source/references.rst b/source/references.rst
> >> index 961fa20..8400e96 100644
> >> --- a/source/references.rst
> >> +++ b/source/references.rst
> >> @@ -23,3 +23,7 @@
> >>.. [EPAPR] *Power.org Standard for Embedded Power Architecture
> >>   Platform Requirements*, power.org, 2011,
> >>
> >> https://www.power.org/documentation/power-org-standard-for-embedded-power-architecture-platform-requirements-epapr-v1-1-2/
> >> 

Re: [PATCH 1/1] GetMemoryMap(), handling of no-map DT property

[Ard Biesheuvel]

On Tue, 15 Sep 2020 at 15:22, Grant Likely  wrote:
>
> On 15/09/2020 09:33, Heinrich Schuchardt wrote:
> > Closes: #52
> >
> > The no-map property of the /reserved-memory device tree nodes is used to
> > signal that a memory region shall not be accessed by the operating system,
> > even not via speculative access.
> >
> > /reserved-memory nodes without the no-map property describe memory that
> > have special usage by the operating system.
> >
> > This difference has to be reflected in the memory map returned by
> > GetMemoryMap().
> >
> > Signed-off-by: Heinrich Schuchardt 
> > ---
> >   source/chapter2-uefi.rst | 13 +
> >   source/references.rst|  4 
> >   2 files changed, 17 insertions(+)
> >
> > diff --git a/source/chapter2-uefi.rst b/source/chapter2-uefi.rst
> > index 74ef70e..f410c57 100644
> > --- a/source/chapter2-uefi.rst
> > +++ b/source/chapter2-uefi.rst
> > @@ -74,6 +74,19 @@ that virtual addresses must equal physical addresses.
> >
> >   The default RAM allocated attribute must be EFI_MEMORY_WB.
> >
> > +In the device tree reserved memory in modelled as a /reserved-memory nodes
> > +[RESMEM]_. The reserved-memory node MAY carry either the no-map or the 
> > resue
> > +property. It MUST NOT carry both properties as this would be contradictary.
> > +
> After having looked at reserved-memory.txt in the kernel and the
> devicetree spec, I think this should just go straight into dtspec or
> into the kernel tree. I drafted a couple patches yesterday that first
> imports /reserved-memory into dtspec, and then adds the UEFI
> annotations. Here's the current patch for the latter:
>
> 
>
> diff --git a/source/chapter3-devicenodes.rst
> b/source/chapter3-devicenodes.rst
> index 3043b8a..647e487 100644
> --- a/source/chapter3-devicenodes.rst
> +++ b/source/chapter3-devicenodes.rst
> @@ -160,6 +160,12 @@ If the VLE storage attribute is supported, with VLE=0.
>   .. note:: All other standard properties (section
>  :ref:`sect-standard-properties`) are allowed but are optional.
>
> +``/memory`` node and UEFI
> +~~
> +
> +When booting via [UEFI]_, the system memory map is obtained via the
> +GetMemoryMap() UEFI boot time service as defined in [UEFI]_ § 7.2,
> +and if present, the OS must ignore any ``/memory`` nodes.
>

This should cover /memreserve/ entries as well.

>   ``/memory`` Examples
>   
> @@ -314,6 +320,9 @@ is ignored.
>   The ``no-map`` and ``reusable`` properties are mutually exclusive and
> both must
>   not be used together in the same node.
>
> +Dynamic reserved memory regions must not listed in the [UEFI]_ memory map

not be listed

> +because they are allocated by the OS after exiting firmware boot services.
> +
>   Linux implementation notes:
>
>   - If a ``linux,cma-default`` property is present, then Linux will use the
> @@ -341,6 +350,19 @@ nodes by adding a ``memory-region`` property to the
> device node.
>  Usage legend: R=Required, O=Optional, OR=Optional but Recommended,
> SD=See Definition
>
> ===
>
> +``/reserved-memory`` and UEFI
> +~
> +When booting via [UEFI]_, static ``/reserved-memory`` regions must
> +also be listed in the system memory map obtained via the GetMemoryMap()
> +UEFI boot time service as defined in [UEFI]_ § 7.2.
> +The reserved memory regions need to be included in the UEFI memory map to
> +protect them from memory allocations by UEFI applications.
> +
> +Reserved regions with the ``no-map`` property must be listed in the memory
> +map with type ``EfiReservedMemoryType``.
> +All other reserved regions must be listed with the type
> +``EfiBootServicesData``.
> +
>   ``/reserved-memory`` Example
>   
>
> diff --git a/source/references.rst b/source/references.rst
> index 961fa20..8400e96 100644
> --- a/source/references.rst
> +++ b/source/references.rst
> @@ -23,3 +23,7 @@
>   .. [EPAPR] *Power.org Standard for Embedded Power Architecture
>  Platform Requirements*, power.org, 2011,
>
> https://www.power.org/documentation/power-org-standard-for-embedded-power-architecture-platform-requirements-epapr-v1-1-2/
> +
> +.. [UEFI] `Unified Extensable Firmware Interface Specification v2.8
> Errata A
> +
> `_,
> +   February 2020, `UEFI Forum `_
> IMPORTANT NOTICE: The contents of this email and any attachments are 
> confidential and may also be privileged. If you are not the intended 
> recipient, please notify the sender immediately and do not disclose the 
> contents to any other person, use it for any purpose, or store or copy the 
> information in any medium. Thank you.
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Re: [PATCH 1/1] GetMemoryMap(), handling of no-map DT property

[Grant Likely]

On 15/09/2020 09:33, Heinrich Schuchardt wrote:

Closes: #52

The no-map property of the /reserved-memory device tree nodes is used to
signal that a memory region shall not be accessed by the operating system,
even not via speculative access.

/reserved-memory nodes without the no-map property describe memory that
have special usage by the operating system.

This difference has to be reflected in the memory map returned by
GetMemoryMap().

Signed-off-by: Heinrich Schuchardt 
---
  source/chapter2-uefi.rst | 13 +
  source/references.rst|  4 
  2 files changed, 17 insertions(+)

diff --git a/source/chapter2-uefi.rst b/source/chapter2-uefi.rst
index 74ef70e..f410c57 100644
--- a/source/chapter2-uefi.rst
+++ b/source/chapter2-uefi.rst
@@ -74,6 +74,19 @@ that virtual addresses must equal physical addresses.

  The default RAM allocated attribute must be EFI_MEMORY_WB.

+In the device tree reserved memory in modelled as a /reserved-memory nodes
+[RESMEM]_. The reserved-memory node MAY carry either the no-map or the resue
+property. It MUST NOT carry both properties as this would be contradictary.
+

After having looked at reserved-memory.txt in the kernel and the
devicetree spec, I think this should just go straight into dtspec or
into the kernel tree. I drafted a couple patches yesterday that first
imports /reserved-memory into dtspec, and then adds the UEFI
annotations. Here's the current patch for the latter:



diff --git a/source/chapter3-devicenodes.rst
b/source/chapter3-devicenodes.rst
index 3043b8a..647e487 100644
--- a/source/chapter3-devicenodes.rst
+++ b/source/chapter3-devicenodes.rst
@@ -160,6 +160,12 @@ If the VLE storage attribute is supported, with VLE=0.
 .. note:: All other standard properties (section
:ref:`sect-standard-properties`) are allowed but are optional.

+``/memory`` node and UEFI
+~~
+
+When booting via [UEFI]_, the system memory map is obtained via the
+GetMemoryMap() UEFI boot time service as defined in [UEFI]_ § 7.2,
+and if present, the OS must ignore any ``/memory`` nodes.

 ``/memory`` Examples
 
@@ -314,6 +320,9 @@ is ignored.
 The ``no-map`` and ``reusable`` properties are mutually exclusive and
both must
 not be used together in the same node.

+Dynamic reserved memory regions must not listed in the [UEFI]_ memory map
+because they are allocated by the OS after exiting firmware boot services.
+
 Linux implementation notes:

 - If a ``linux,cma-default`` property is present, then Linux will use the
@@ -341,6 +350,19 @@ nodes by adding a ``memory-region`` property to the
device node.
Usage legend: R=Required, O=Optional, OR=Optional but Recommended,
SD=See Definition

===

+``/reserved-memory`` and UEFI
+~
+When booting via [UEFI]_, static ``/reserved-memory`` regions must
+also be listed in the system memory map obtained via the GetMemoryMap()
+UEFI boot time service as defined in [UEFI]_ § 7.2.
+The reserved memory regions need to be included in the UEFI memory map to
+protect them from memory allocations by UEFI applications.
+
+Reserved regions with the ``no-map`` property must be listed in the memory
+map with type ``EfiReservedMemoryType``.
+All other reserved regions must be listed with the type
+``EfiBootServicesData``.
+
 ``/reserved-memory`` Example
 

diff --git a/source/references.rst b/source/references.rst
index 961fa20..8400e96 100644
--- a/source/references.rst
+++ b/source/references.rst
@@ -23,3 +23,7 @@
 .. [EPAPR] *Power.org Standard for Embedded Power Architecture
Platform Requirements*, power.org, 2011,

https://www.power.org/documentation/power-org-standard-for-embedded-power-architecture-platform-requirements-epapr-v1-1-2/
+
+.. [UEFI] `Unified Extensable Firmware Interface Specification v2.8
Errata A
+
`_,
+   February 2020, `UEFI Forum `_
IMPORTANT NOTICE: The contents of this email and any attachments are 
confidential and may also be privileged. If you are not the intended recipient, 
please notify the sender immediately and do not disclose the contents to any 
other person, use it for any purpose, or store or copy the information in any 
medium. Thank you.
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[PATCH 1/1] GetMemoryMap(), handling of no-map DT property

[Heinrich Schuchardt]

Closes: #52

The no-map property of the /reserved-memory device tree nodes is used to
signal that a memory region shall not be accessed by the operating system,
even not via speculative access.

/reserved-memory nodes without the no-map property describe memory that
have special usage by the operating system.

This difference has to be reflected in the memory map returned by
GetMemoryMap().

Signed-off-by: Heinrich Schuchardt 
---
 source/chapter2-uefi.rst | 13 +
 source/references.rst|  4 
 2 files changed, 17 insertions(+)

diff --git a/source/chapter2-uefi.rst b/source/chapter2-uefi.rst
index 74ef70e..f410c57 100644
--- a/source/chapter2-uefi.rst
+++ b/source/chapter2-uefi.rst
@@ -74,6 +74,19 @@ that virtual addresses must equal physical addresses.

 The default RAM allocated attribute must be EFI_MEMORY_WB.

+In the device tree reserved memory in modelled as a /reserved-memory nodes
+[RESMEM]_. The reserved-memory node MAY carry either the no-map or the resue
+property. It MUST NOT carry both properties as this would be contradictary.
+
+A 'no-map' reserved memory node describes memory that the UEFI payload MUST NOT
+access. It MUST be modelled as a EfiReservedMemoryType entry in the memory map.
+
+A reserved memory without the 'no-map' describes memory that MAY be used by the
+UEFI payload after ExitBootServices(). It MUST be modelled as a memory map 
entry
+that can only be used by the UEFI payload after ExitBootServices(). It
+is recommended to use EfiBootServicesData. The node MUST NOT be modelled as
+EfiReservedMemoryType and NOT as EfiConventionalMemory.
+
 Configuration Tables
 

diff --git a/source/references.rst b/source/references.rst
index 1eb0509..2434137 100644
--- a/source/references.rst
+++ b/source/references.rst
@@ -16,6 +16,10 @@

`_
30 January 2015, `Arm Limited `_

+.. [RESMEM] `Reserved memory regions
+   
`_,
+   21 July 2020, Linux kernel
+
 .. [SBBR] `Arm Server Base Boot Requirements specification Issue B (v1.0)

`_
8 March 2016, `Arm Limited `_
--
2.28.0

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