Re: [PATCH kernel v8 10/10] KVM: PPC: VFIO: Add in-kernel acceleration for VFIO

[David Gibson]

On Wed, Mar 15, 2017 at 10:18:18AM -0600, Alex Williamson wrote:
> On Wed, 15 Mar 2017 15:40:14 +1100
> David Gibson  wrote:
> > > > diff --git a/arch/powerpc/kvm/book3s_64_vio.c 
> > > > b/arch/powerpc/kvm/book3s_64_vio.c
> > > > index e96a4590464c..be18cda01e1b 100644
> > > > --- a/arch/powerpc/kvm/book3s_64_vio.c
> > > > +++ b/arch/powerpc/kvm/book3s_64_vio.c
> > > > @@ -28,6 +28,10 @@
> > > >  #include 
> > > >  #include 
> > > >  #include 
> > > > +#include 
> > > > +#include 
> > > > +#include 
> > > > +#include 
> > > >  
> > > >  #include 
> > > >  #include 
> > > > @@ -40,6 +44,36 @@
> > > >  #include 
> > > >  #include 
> > > >  #include 
> > > > +#include 
> > > > +
> > > > +static void kvm_vfio_group_put_external_user(struct vfio_group 
> > > > *vfio_group)
> > > > +{
> > > > +   void (*fn)(struct vfio_group *);
> > > > +
> > > > +   fn = symbol_get(vfio_group_put_external_user);
> > > > +   if (WARN_ON(!fn))
> > > > +   return;
> > > > +
> > > > +   fn(vfio_group);
> > > > +
> > > > +   symbol_put(vfio_group_put_external_user);
> > > > +}
> > > > +
> > > > +static int kvm_vfio_external_user_iommu_id(struct vfio_group 
> > > > *vfio_group)
> > > > +{
> > > > +   int (*fn)(struct vfio_group *);
> > > > +   int ret = -1;
> > > > +
> > > > +   fn = symbol_get(vfio_external_user_iommu_id);
> > > > +   if (!fn)
> > > > +   return ret;
> > > > +
> > > > +   ret = fn(vfio_group);
> > > > +
> > > > +   symbol_put(vfio_external_user_iommu_id);
> > > > +
> > > > +   return ret;
> > > > +}  
> > > 
> > > 
> > > Ugh.  This feels so wrong.  Why can't you have kvm-vfio pass the
> > > iommu_group?  Why do you need to hold this additional vfio_group
> > > reference?  
> > 
> > Keeping the vfio_group reference makes sense to me, since we don't
> > want the vfio context for the group to go away while it's attached to
> > the LIOBN.
> 
> But there's already a reference for that, it's taken by
> KVM_DEV_VFIO_GROUP_ADD and held until KVM_DEV_VFIO_GROUP_DEL.  Both the
> DEL path and the cleanup path call kvm_spapr_tce_release_iommu_group()
> before releasing that reference, so it seems entirely redundant.

Oh, good point.  And we already verify that the group has been ADDed
before setting the LIOBN association.

> > However, going via the iommu_id rather than just having an interface
> > to directly grab the iommu group from the vfio_group seems bizarre to
> > me.  I'm ok with cleaning that up later, however.
> 
> We have kvm_spapr_tce_attach_iommu_group() and
> kvm_spapr_tce_release_iommu_group(), but both take a vfio_group, not an
> iommu_group as a parameter.  I don't particularly have a problem with
> the vfio_group -> iommu ID -> iommu_group, but if we drop the extra
> vfio_group reference and pass the iommu_group itself to these functions
> then we can keep all the symbol reference stuff in the kvm-vfio glue
> layer.  Thanks,

Makes sense.

-- 
David Gibson| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson


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Re: [PATCH kernel v8 10/10] KVM: PPC: VFIO: Add in-kernel acceleration for VFIO

[Alexey Kardashevskiy]

On 16/03/17 03:39, Alex Williamson wrote:
> On Thu, 16 Mar 2017 00:21:07 +1100
> Alexey Kardashevskiy  wrote:
> 
>> On 15/03/17 08:05, Alex Williamson wrote:
>>> On Fri, 10 Mar 2017 14:53:37 +1100
>>> Alexey Kardashevskiy  wrote:
>>>   
 This allows the host kernel to handle H_PUT_TCE, H_PUT_TCE_INDIRECT
 and H_STUFF_TCE requests targeted an IOMMU TCE table used for VFIO
 without passing them to user space which saves time on switching
 to user space and back.

 This adds H_PUT_TCE/H_PUT_TCE_INDIRECT/H_STUFF_TCE handlers to KVM.
 KVM tries to handle a TCE request in the real mode, if failed
 it passes the request to the virtual mode to complete the operation.
 If it a virtual mode handler fails, the request is passed to
 the user space; this is not expected to happen though.

 To avoid dealing with page use counters (which is tricky in real mode),
 this only accelerates SPAPR TCE IOMMU v2 clients which are required
 to pre-register the userspace memory. The very first TCE request will
 be handled in the VFIO SPAPR TCE driver anyway as the userspace view
 of the TCE table (iommu_table::it_userspace) is not allocated till
 the very first mapping happens and we cannot call vmalloc in real mode.

 If we fail to update a hardware IOMMU table unexpected reason, we just
 clear it and move on as there is nothing really we can do about it -
 for example, if we hot plug a VFIO device to a guest, existing TCE tables
 will be mirrored automatically to the hardware and there is no interface
 to report to the guest about possible failures.

 This adds new attribute - KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE - to
 the VFIO KVM device. It takes a VFIO group fd and SPAPR TCE table fd
 and associates a physical IOMMU table with the SPAPR TCE table (which
 is a guest view of the hardware IOMMU table). The iommu_table object
 is cached and referenced so we do not have to look up for it in real mode.

 This does not implement the UNSET counterpart as there is no use for it -
 once the acceleration is enabled, the existing userspace won't
 disable it unless a VFIO container is destroyed; this adds necessary
 cleanup to the KVM_DEV_VFIO_GROUP_DEL handler.

 As this creates a descriptor per IOMMU table-LIOBN couple (called
 kvmppc_spapr_tce_iommu_table), it is possible to have several
 descriptors with the same iommu_table (hardware IOMMU table) attached
 to the same LIOBN; we do not remove duplicates though as
 iommu_table_ops::exchange not just update a TCE entry (which is
 shared among IOMMU groups) but also invalidates the TCE cache
 (one per IOMMU group).

 This advertises the new KVM_CAP_SPAPR_TCE_VFIO capability to the user
 space.

 This adds real mode version of WARN_ON_ONCE() as the generic version
 causes problems with rcu_sched. Since we testing what vmalloc_to_phys()
 returns in the code, this also adds a check for already existing
 vmalloc_to_phys() call in kvmppc_rm_h_put_tce_indirect().

 This finally makes use of vfio_external_user_iommu_id() which was
 introduced quite some time ago and was considered for removal.

 Tests show that this patch increases transmission speed from 220MB/s
 to 750..1020MB/s on 10Gb network (Chelsea CXGB3 10Gb ethernet card).

 Signed-off-by: Alexey Kardashevskiy 
 ---
 Changes:
 v8:
 * changed all (!pua) checks to return H_TOO_HARD as ioctl() is supposed
 to handle them
 * changed vmalloc_to_phys() callers to return H_HARDWARE
 * changed real mode iommu_tce_xchg_rm() callers to return H_TOO_HARD
 and added a comment about this in the code
 * changed virtual mode iommu_tce_xchg() callers to return H_HARDWARE
 and do WARN_ON
 * added WARN_ON_ONCE_RM(!rmap) in kvmppc_rm_h_put_tce_indirect() to
 have all vmalloc_to_phys() callsites covered

 v7:
 * added realmode-friendly WARN_ON_ONCE_RM

 v6:
 * changed handling of errors returned by kvmppc_(rm_)tce_iommu_(un)map()
 * moved kvmppc_gpa_to_ua() to TCE validation

 v5:
 * changed error codes in multiple places
 * added bunch of WARN_ON() in places which should not really happen
 * adde a check that an iommu table is not attached already to LIOBN
 * dropped explicit calls to iommu_tce_clear_param_check/
 iommu_tce_put_param_check as kvmppc_tce_validate/kvmppc_ioba_validate
 call them anyway (since the previous patch)
 * if we fail to update a hardware IOMMU table for unexpected reason,
 this just clears the entry

 v4:
 * added note to the commit log about allowing multiple updates of
 the same IOMMU table;
 * instead of checking for if any memory was preregistered, this
 returns H_TOO_HARD if a specific page was not;
 * fixed 

Re: [PATCH kernel v8 10/10] KVM: PPC: VFIO: Add in-kernel acceleration for VFIO

[Alex Williamson]

On Thu, 16 Mar 2017 00:21:07 +1100
Alexey Kardashevskiy  wrote:

> On 15/03/17 08:05, Alex Williamson wrote:
> > On Fri, 10 Mar 2017 14:53:37 +1100
> > Alexey Kardashevskiy  wrote:
> >   
> >> This allows the host kernel to handle H_PUT_TCE, H_PUT_TCE_INDIRECT
> >> and H_STUFF_TCE requests targeted an IOMMU TCE table used for VFIO
> >> without passing them to user space which saves time on switching
> >> to user space and back.
> >>
> >> This adds H_PUT_TCE/H_PUT_TCE_INDIRECT/H_STUFF_TCE handlers to KVM.
> >> KVM tries to handle a TCE request in the real mode, if failed
> >> it passes the request to the virtual mode to complete the operation.
> >> If it a virtual mode handler fails, the request is passed to
> >> the user space; this is not expected to happen though.
> >>
> >> To avoid dealing with page use counters (which is tricky in real mode),
> >> this only accelerates SPAPR TCE IOMMU v2 clients which are required
> >> to pre-register the userspace memory. The very first TCE request will
> >> be handled in the VFIO SPAPR TCE driver anyway as the userspace view
> >> of the TCE table (iommu_table::it_userspace) is not allocated till
> >> the very first mapping happens and we cannot call vmalloc in real mode.
> >>
> >> If we fail to update a hardware IOMMU table unexpected reason, we just
> >> clear it and move on as there is nothing really we can do about it -
> >> for example, if we hot plug a VFIO device to a guest, existing TCE tables
> >> will be mirrored automatically to the hardware and there is no interface
> >> to report to the guest about possible failures.
> >>
> >> This adds new attribute - KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE - to
> >> the VFIO KVM device. It takes a VFIO group fd and SPAPR TCE table fd
> >> and associates a physical IOMMU table with the SPAPR TCE table (which
> >> is a guest view of the hardware IOMMU table). The iommu_table object
> >> is cached and referenced so we do not have to look up for it in real mode.
> >>
> >> This does not implement the UNSET counterpart as there is no use for it -
> >> once the acceleration is enabled, the existing userspace won't
> >> disable it unless a VFIO container is destroyed; this adds necessary
> >> cleanup to the KVM_DEV_VFIO_GROUP_DEL handler.
> >>
> >> As this creates a descriptor per IOMMU table-LIOBN couple (called
> >> kvmppc_spapr_tce_iommu_table), it is possible to have several
> >> descriptors with the same iommu_table (hardware IOMMU table) attached
> >> to the same LIOBN; we do not remove duplicates though as
> >> iommu_table_ops::exchange not just update a TCE entry (which is
> >> shared among IOMMU groups) but also invalidates the TCE cache
> >> (one per IOMMU group).
> >>
> >> This advertises the new KVM_CAP_SPAPR_TCE_VFIO capability to the user
> >> space.
> >>
> >> This adds real mode version of WARN_ON_ONCE() as the generic version
> >> causes problems with rcu_sched. Since we testing what vmalloc_to_phys()
> >> returns in the code, this also adds a check for already existing
> >> vmalloc_to_phys() call in kvmppc_rm_h_put_tce_indirect().
> >>
> >> This finally makes use of vfio_external_user_iommu_id() which was
> >> introduced quite some time ago and was considered for removal.
> >>
> >> Tests show that this patch increases transmission speed from 220MB/s
> >> to 750..1020MB/s on 10Gb network (Chelsea CXGB3 10Gb ethernet card).
> >>
> >> Signed-off-by: Alexey Kardashevskiy 
> >> ---
> >> Changes:
> >> v8:
> >> * changed all (!pua) checks to return H_TOO_HARD as ioctl() is supposed
> >> to handle them
> >> * changed vmalloc_to_phys() callers to return H_HARDWARE
> >> * changed real mode iommu_tce_xchg_rm() callers to return H_TOO_HARD
> >> and added a comment about this in the code
> >> * changed virtual mode iommu_tce_xchg() callers to return H_HARDWARE
> >> and do WARN_ON
> >> * added WARN_ON_ONCE_RM(!rmap) in kvmppc_rm_h_put_tce_indirect() to
> >> have all vmalloc_to_phys() callsites covered
> >>
> >> v7:
> >> * added realmode-friendly WARN_ON_ONCE_RM
> >>
> >> v6:
> >> * changed handling of errors returned by kvmppc_(rm_)tce_iommu_(un)map()
> >> * moved kvmppc_gpa_to_ua() to TCE validation
> >>
> >> v5:
> >> * changed error codes in multiple places
> >> * added bunch of WARN_ON() in places which should not really happen
> >> * adde a check that an iommu table is not attached already to LIOBN
> >> * dropped explicit calls to iommu_tce_clear_param_check/
> >> iommu_tce_put_param_check as kvmppc_tce_validate/kvmppc_ioba_validate
> >> call them anyway (since the previous patch)
> >> * if we fail to update a hardware IOMMU table for unexpected reason,
> >> this just clears the entry
> >>
> >> v4:
> >> * added note to the commit log about allowing multiple updates of
> >> the same IOMMU table;
> >> * instead of checking for if any memory was preregistered, this
> >> returns H_TOO_HARD if a specific page was not;
> >> * fixed comments from v3 about error handling in many places;

Re: [PATCH kernel v8 10/10] KVM: PPC: VFIO: Add in-kernel acceleration for VFIO

[Alex Williamson]

On Wed, 15 Mar 2017 15:40:14 +1100
David Gibson  wrote:
> > > diff --git a/arch/powerpc/kvm/book3s_64_vio.c 
> > > b/arch/powerpc/kvm/book3s_64_vio.c
> > > index e96a4590464c..be18cda01e1b 100644
> > > --- a/arch/powerpc/kvm/book3s_64_vio.c
> > > +++ b/arch/powerpc/kvm/book3s_64_vio.c
> > > @@ -28,6 +28,10 @@
> > >  #include 
> > >  #include 
> > >  #include 
> > > +#include 
> > > +#include 
> > > +#include 
> > > +#include 
> > >  
> > >  #include 
> > >  #include 
> > > @@ -40,6 +44,36 @@
> > >  #include 
> > >  #include 
> > >  #include 
> > > +#include 
> > > +
> > > +static void kvm_vfio_group_put_external_user(struct vfio_group 
> > > *vfio_group)
> > > +{
> > > + void (*fn)(struct vfio_group *);
> > > +
> > > + fn = symbol_get(vfio_group_put_external_user);
> > > + if (WARN_ON(!fn))
> > > + return;
> > > +
> > > + fn(vfio_group);
> > > +
> > > + symbol_put(vfio_group_put_external_user);
> > > +}
> > > +
> > > +static int kvm_vfio_external_user_iommu_id(struct vfio_group *vfio_group)
> > > +{
> > > + int (*fn)(struct vfio_group *);
> > > + int ret = -1;
> > > +
> > > + fn = symbol_get(vfio_external_user_iommu_id);
> > > + if (!fn)
> > > + return ret;
> > > +
> > > + ret = fn(vfio_group);
> > > +
> > > + symbol_put(vfio_external_user_iommu_id);
> > > +
> > > + return ret;
> > > +}  
> > 
> > 
> > Ugh.  This feels so wrong.  Why can't you have kvm-vfio pass the
> > iommu_group?  Why do you need to hold this additional vfio_group
> > reference?  
> 
> Keeping the vfio_group reference makes sense to me, since we don't
> want the vfio context for the group to go away while it's attached to
> the LIOBN.

But there's already a reference for that, it's taken by
KVM_DEV_VFIO_GROUP_ADD and held until KVM_DEV_VFIO_GROUP_DEL.  Both the
DEL path and the cleanup path call kvm_spapr_tce_release_iommu_group()
before releasing that reference, so it seems entirely redundant.

> However, going via the iommu_id rather than just having an interface
> to directly grab the iommu group from the vfio_group seems bizarre to
> me.  I'm ok with cleaning that up later, however.

We have kvm_spapr_tce_attach_iommu_group() and
kvm_spapr_tce_release_iommu_group(), but both take a vfio_group, not an
iommu_group as a parameter.  I don't particularly have a problem with
the vfio_group -> iommu ID -> iommu_group, but if we drop the extra
vfio_group reference and pass the iommu_group itself to these functions
then we can keep all the symbol reference stuff in the kvm-vfio glue
layer.  Thanks,

Alex

Re: [PATCH kernel v8 10/10] KVM: PPC: VFIO: Add in-kernel acceleration for VFIO

[Alexey Kardashevskiy]

On 15/03/17 08:05, Alex Williamson wrote:
> On Fri, 10 Mar 2017 14:53:37 +1100
> Alexey Kardashevskiy  wrote:
> 
>> This allows the host kernel to handle H_PUT_TCE, H_PUT_TCE_INDIRECT
>> and H_STUFF_TCE requests targeted an IOMMU TCE table used for VFIO
>> without passing them to user space which saves time on switching
>> to user space and back.
>>
>> This adds H_PUT_TCE/H_PUT_TCE_INDIRECT/H_STUFF_TCE handlers to KVM.
>> KVM tries to handle a TCE request in the real mode, if failed
>> it passes the request to the virtual mode to complete the operation.
>> If it a virtual mode handler fails, the request is passed to
>> the user space; this is not expected to happen though.
>>
>> To avoid dealing with page use counters (which is tricky in real mode),
>> this only accelerates SPAPR TCE IOMMU v2 clients which are required
>> to pre-register the userspace memory. The very first TCE request will
>> be handled in the VFIO SPAPR TCE driver anyway as the userspace view
>> of the TCE table (iommu_table::it_userspace) is not allocated till
>> the very first mapping happens and we cannot call vmalloc in real mode.
>>
>> If we fail to update a hardware IOMMU table unexpected reason, we just
>> clear it and move on as there is nothing really we can do about it -
>> for example, if we hot plug a VFIO device to a guest, existing TCE tables
>> will be mirrored automatically to the hardware and there is no interface
>> to report to the guest about possible failures.
>>
>> This adds new attribute - KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE - to
>> the VFIO KVM device. It takes a VFIO group fd and SPAPR TCE table fd
>> and associates a physical IOMMU table with the SPAPR TCE table (which
>> is a guest view of the hardware IOMMU table). The iommu_table object
>> is cached and referenced so we do not have to look up for it in real mode.
>>
>> This does not implement the UNSET counterpart as there is no use for it -
>> once the acceleration is enabled, the existing userspace won't
>> disable it unless a VFIO container is destroyed; this adds necessary
>> cleanup to the KVM_DEV_VFIO_GROUP_DEL handler.
>>
>> As this creates a descriptor per IOMMU table-LIOBN couple (called
>> kvmppc_spapr_tce_iommu_table), it is possible to have several
>> descriptors with the same iommu_table (hardware IOMMU table) attached
>> to the same LIOBN; we do not remove duplicates though as
>> iommu_table_ops::exchange not just update a TCE entry (which is
>> shared among IOMMU groups) but also invalidates the TCE cache
>> (one per IOMMU group).
>>
>> This advertises the new KVM_CAP_SPAPR_TCE_VFIO capability to the user
>> space.
>>
>> This adds real mode version of WARN_ON_ONCE() as the generic version
>> causes problems with rcu_sched. Since we testing what vmalloc_to_phys()
>> returns in the code, this also adds a check for already existing
>> vmalloc_to_phys() call in kvmppc_rm_h_put_tce_indirect().
>>
>> This finally makes use of vfio_external_user_iommu_id() which was
>> introduced quite some time ago and was considered for removal.
>>
>> Tests show that this patch increases transmission speed from 220MB/s
>> to 750..1020MB/s on 10Gb network (Chelsea CXGB3 10Gb ethernet card).
>>
>> Signed-off-by: Alexey Kardashevskiy 
>> ---
>> Changes:
>> v8:
>> * changed all (!pua) checks to return H_TOO_HARD as ioctl() is supposed
>> to handle them
>> * changed vmalloc_to_phys() callers to return H_HARDWARE
>> * changed real mode iommu_tce_xchg_rm() callers to return H_TOO_HARD
>> and added a comment about this in the code
>> * changed virtual mode iommu_tce_xchg() callers to return H_HARDWARE
>> and do WARN_ON
>> * added WARN_ON_ONCE_RM(!rmap) in kvmppc_rm_h_put_tce_indirect() to
>> have all vmalloc_to_phys() callsites covered
>>
>> v7:
>> * added realmode-friendly WARN_ON_ONCE_RM
>>
>> v6:
>> * changed handling of errors returned by kvmppc_(rm_)tce_iommu_(un)map()
>> * moved kvmppc_gpa_to_ua() to TCE validation
>>
>> v5:
>> * changed error codes in multiple places
>> * added bunch of WARN_ON() in places which should not really happen
>> * adde a check that an iommu table is not attached already to LIOBN
>> * dropped explicit calls to iommu_tce_clear_param_check/
>> iommu_tce_put_param_check as kvmppc_tce_validate/kvmppc_ioba_validate
>> call them anyway (since the previous patch)
>> * if we fail to update a hardware IOMMU table for unexpected reason,
>> this just clears the entry
>>
>> v4:
>> * added note to the commit log about allowing multiple updates of
>> the same IOMMU table;
>> * instead of checking for if any memory was preregistered, this
>> returns H_TOO_HARD if a specific page was not;
>> * fixed comments from v3 about error handling in many places;
>> * simplified TCE handlers and merged IOMMU parts inline - for example,
>> there used to be kvmppc_h_put_tce_iommu(), now it is merged into
>> kvmppc_h_put_tce(); this allows to check IOBA boundaries against
>> the first attached table only (makes the code simpler);
>>
>> v3:

Re: [PATCH kernel v8 10/10] KVM: PPC: VFIO: Add in-kernel acceleration for VFIO

[David Gibson]

On Tue, Mar 14, 2017 at 03:05:27PM -0600, Alex Williamson wrote:
> On Fri, 10 Mar 2017 14:53:37 +1100
> Alexey Kardashevskiy  wrote:
> 
> > This allows the host kernel to handle H_PUT_TCE, H_PUT_TCE_INDIRECT
> > and H_STUFF_TCE requests targeted an IOMMU TCE table used for VFIO
> > without passing them to user space which saves time on switching
> > to user space and back.
> > 
> > This adds H_PUT_TCE/H_PUT_TCE_INDIRECT/H_STUFF_TCE handlers to KVM.
> > KVM tries to handle a TCE request in the real mode, if failed
> > it passes the request to the virtual mode to complete the operation.
> > If it a virtual mode handler fails, the request is passed to
> > the user space; this is not expected to happen though.
> > 
> > To avoid dealing with page use counters (which is tricky in real mode),
> > this only accelerates SPAPR TCE IOMMU v2 clients which are required
> > to pre-register the userspace memory. The very first TCE request will
> > be handled in the VFIO SPAPR TCE driver anyway as the userspace view
> > of the TCE table (iommu_table::it_userspace) is not allocated till
> > the very first mapping happens and we cannot call vmalloc in real mode.
> > 
> > If we fail to update a hardware IOMMU table unexpected reason, we just
> > clear it and move on as there is nothing really we can do about it -
> > for example, if we hot plug a VFIO device to a guest, existing TCE tables
> > will be mirrored automatically to the hardware and there is no interface
> > to report to the guest about possible failures.
> > 
> > This adds new attribute - KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE - to
> > the VFIO KVM device. It takes a VFIO group fd and SPAPR TCE table fd
> > and associates a physical IOMMU table with the SPAPR TCE table (which
> > is a guest view of the hardware IOMMU table). The iommu_table object
> > is cached and referenced so we do not have to look up for it in real mode.
> > 
> > This does not implement the UNSET counterpart as there is no use for it -
> > once the acceleration is enabled, the existing userspace won't
> > disable it unless a VFIO container is destroyed; this adds necessary
> > cleanup to the KVM_DEV_VFIO_GROUP_DEL handler.
> > 
> > As this creates a descriptor per IOMMU table-LIOBN couple (called
> > kvmppc_spapr_tce_iommu_table), it is possible to have several
> > descriptors with the same iommu_table (hardware IOMMU table) attached
> > to the same LIOBN; we do not remove duplicates though as
> > iommu_table_ops::exchange not just update a TCE entry (which is
> > shared among IOMMU groups) but also invalidates the TCE cache
> > (one per IOMMU group).
> > 
> > This advertises the new KVM_CAP_SPAPR_TCE_VFIO capability to the user
> > space.
> > 
> > This adds real mode version of WARN_ON_ONCE() as the generic version
> > causes problems with rcu_sched. Since we testing what vmalloc_to_phys()
> > returns in the code, this also adds a check for already existing
> > vmalloc_to_phys() call in kvmppc_rm_h_put_tce_indirect().
> > 
> > This finally makes use of vfio_external_user_iommu_id() which was
> > introduced quite some time ago and was considered for removal.
> > 
> > Tests show that this patch increases transmission speed from 220MB/s
> > to 750..1020MB/s on 10Gb network (Chelsea CXGB3 10Gb ethernet card).
> > 
> > Signed-off-by: Alexey Kardashevskiy 
> > ---
> > Changes:
> > v8:
> > * changed all (!pua) checks to return H_TOO_HARD as ioctl() is supposed
> > to handle them
> > * changed vmalloc_to_phys() callers to return H_HARDWARE
> > * changed real mode iommu_tce_xchg_rm() callers to return H_TOO_HARD
> > and added a comment about this in the code
> > * changed virtual mode iommu_tce_xchg() callers to return H_HARDWARE
> > and do WARN_ON
> > * added WARN_ON_ONCE_RM(!rmap) in kvmppc_rm_h_put_tce_indirect() to
> > have all vmalloc_to_phys() callsites covered
> > 
> > v7:
> > * added realmode-friendly WARN_ON_ONCE_RM
> > 
> > v6:
> > * changed handling of errors returned by kvmppc_(rm_)tce_iommu_(un)map()
> > * moved kvmppc_gpa_to_ua() to TCE validation
> > 
> > v5:
> > * changed error codes in multiple places
> > * added bunch of WARN_ON() in places which should not really happen
> > * adde a check that an iommu table is not attached already to LIOBN
> > * dropped explicit calls to iommu_tce_clear_param_check/
> > iommu_tce_put_param_check as kvmppc_tce_validate/kvmppc_ioba_validate
> > call them anyway (since the previous patch)
> > * if we fail to update a hardware IOMMU table for unexpected reason,
> > this just clears the entry
> > 
> > v4:
> > * added note to the commit log about allowing multiple updates of
> > the same IOMMU table;
> > * instead of checking for if any memory was preregistered, this
> > returns H_TOO_HARD if a specific page was not;
> > * fixed comments from v3 about error handling in many places;
> > * simplified TCE handlers and merged IOMMU parts inline - for example,
> > there used to be kvmppc_h_put_tce_iommu(), now it is merged into
> > 

Re: [PATCH kernel v8 10/10] KVM: PPC: VFIO: Add in-kernel acceleration for VFIO

[Alex Williamson]

On Fri, 10 Mar 2017 14:53:37 +1100
Alexey Kardashevskiy  wrote:

> This allows the host kernel to handle H_PUT_TCE, H_PUT_TCE_INDIRECT
> and H_STUFF_TCE requests targeted an IOMMU TCE table used for VFIO
> without passing them to user space which saves time on switching
> to user space and back.
> 
> This adds H_PUT_TCE/H_PUT_TCE_INDIRECT/H_STUFF_TCE handlers to KVM.
> KVM tries to handle a TCE request in the real mode, if failed
> it passes the request to the virtual mode to complete the operation.
> If it a virtual mode handler fails, the request is passed to
> the user space; this is not expected to happen though.
> 
> To avoid dealing with page use counters (which is tricky in real mode),
> this only accelerates SPAPR TCE IOMMU v2 clients which are required
> to pre-register the userspace memory. The very first TCE request will
> be handled in the VFIO SPAPR TCE driver anyway as the userspace view
> of the TCE table (iommu_table::it_userspace) is not allocated till
> the very first mapping happens and we cannot call vmalloc in real mode.
> 
> If we fail to update a hardware IOMMU table unexpected reason, we just
> clear it and move on as there is nothing really we can do about it -
> for example, if we hot plug a VFIO device to a guest, existing TCE tables
> will be mirrored automatically to the hardware and there is no interface
> to report to the guest about possible failures.
> 
> This adds new attribute - KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE - to
> the VFIO KVM device. It takes a VFIO group fd and SPAPR TCE table fd
> and associates a physical IOMMU table with the SPAPR TCE table (which
> is a guest view of the hardware IOMMU table). The iommu_table object
> is cached and referenced so we do not have to look up for it in real mode.
> 
> This does not implement the UNSET counterpart as there is no use for it -
> once the acceleration is enabled, the existing userspace won't
> disable it unless a VFIO container is destroyed; this adds necessary
> cleanup to the KVM_DEV_VFIO_GROUP_DEL handler.
> 
> As this creates a descriptor per IOMMU table-LIOBN couple (called
> kvmppc_spapr_tce_iommu_table), it is possible to have several
> descriptors with the same iommu_table (hardware IOMMU table) attached
> to the same LIOBN; we do not remove duplicates though as
> iommu_table_ops::exchange not just update a TCE entry (which is
> shared among IOMMU groups) but also invalidates the TCE cache
> (one per IOMMU group).
> 
> This advertises the new KVM_CAP_SPAPR_TCE_VFIO capability to the user
> space.
> 
> This adds real mode version of WARN_ON_ONCE() as the generic version
> causes problems with rcu_sched. Since we testing what vmalloc_to_phys()
> returns in the code, this also adds a check for already existing
> vmalloc_to_phys() call in kvmppc_rm_h_put_tce_indirect().
> 
> This finally makes use of vfio_external_user_iommu_id() which was
> introduced quite some time ago and was considered for removal.
> 
> Tests show that this patch increases transmission speed from 220MB/s
> to 750..1020MB/s on 10Gb network (Chelsea CXGB3 10Gb ethernet card).
> 
> Signed-off-by: Alexey Kardashevskiy 
> ---
> Changes:
> v8:
> * changed all (!pua) checks to return H_TOO_HARD as ioctl() is supposed
> to handle them
> * changed vmalloc_to_phys() callers to return H_HARDWARE
> * changed real mode iommu_tce_xchg_rm() callers to return H_TOO_HARD
> and added a comment about this in the code
> * changed virtual mode iommu_tce_xchg() callers to return H_HARDWARE
> and do WARN_ON
> * added WARN_ON_ONCE_RM(!rmap) in kvmppc_rm_h_put_tce_indirect() to
> have all vmalloc_to_phys() callsites covered
> 
> v7:
> * added realmode-friendly WARN_ON_ONCE_RM
> 
> v6:
> * changed handling of errors returned by kvmppc_(rm_)tce_iommu_(un)map()
> * moved kvmppc_gpa_to_ua() to TCE validation
> 
> v5:
> * changed error codes in multiple places
> * added bunch of WARN_ON() in places which should not really happen
> * adde a check that an iommu table is not attached already to LIOBN
> * dropped explicit calls to iommu_tce_clear_param_check/
> iommu_tce_put_param_check as kvmppc_tce_validate/kvmppc_ioba_validate
> call them anyway (since the previous patch)
> * if we fail to update a hardware IOMMU table for unexpected reason,
> this just clears the entry
> 
> v4:
> * added note to the commit log about allowing multiple updates of
> the same IOMMU table;
> * instead of checking for if any memory was preregistered, this
> returns H_TOO_HARD if a specific page was not;
> * fixed comments from v3 about error handling in many places;
> * simplified TCE handlers and merged IOMMU parts inline - for example,
> there used to be kvmppc_h_put_tce_iommu(), now it is merged into
> kvmppc_h_put_tce(); this allows to check IOBA boundaries against
> the first attached table only (makes the code simpler);
> 
> v3:
> * simplified not to use VFIO group notifiers
> * reworked cleanup, should be cleaner/simpler now
> 
> v2:
> * reworked to use new 

Re: [PATCH kernel v8 10/10] KVM: PPC: VFIO: Add in-kernel acceleration for VFIO

[David Gibson]

On Fri, Mar 10, 2017 at 02:53:37PM +1100, Alexey Kardashevskiy wrote:
> This allows the host kernel to handle H_PUT_TCE, H_PUT_TCE_INDIRECT
> and H_STUFF_TCE requests targeted an IOMMU TCE table used for VFIO
> without passing them to user space which saves time on switching
> to user space and back.
> 
> This adds H_PUT_TCE/H_PUT_TCE_INDIRECT/H_STUFF_TCE handlers to KVM.
> KVM tries to handle a TCE request in the real mode, if failed
> it passes the request to the virtual mode to complete the operation.
> If it a virtual mode handler fails, the request is passed to
> the user space; this is not expected to happen though.
> 
> To avoid dealing with page use counters (which is tricky in real mode),
> this only accelerates SPAPR TCE IOMMU v2 clients which are required
> to pre-register the userspace memory. The very first TCE request will
> be handled in the VFIO SPAPR TCE driver anyway as the userspace view
> of the TCE table (iommu_table::it_userspace) is not allocated till
> the very first mapping happens and we cannot call vmalloc in real mode.
> 
> If we fail to update a hardware IOMMU table unexpected reason, we just
> clear it and move on as there is nothing really we can do about it -
> for example, if we hot plug a VFIO device to a guest, existing TCE tables
> will be mirrored automatically to the hardware and there is no interface
> to report to the guest about possible failures.
> 
> This adds new attribute - KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE - to
> the VFIO KVM device. It takes a VFIO group fd and SPAPR TCE table fd
> and associates a physical IOMMU table with the SPAPR TCE table (which
> is a guest view of the hardware IOMMU table). The iommu_table object
> is cached and referenced so we do not have to look up for it in real mode.
> 
> This does not implement the UNSET counterpart as there is no use for it -
> once the acceleration is enabled, the existing userspace won't
> disable it unless a VFIO container is destroyed; this adds necessary
> cleanup to the KVM_DEV_VFIO_GROUP_DEL handler.
> 
> As this creates a descriptor per IOMMU table-LIOBN couple (called
> kvmppc_spapr_tce_iommu_table), it is possible to have several
> descriptors with the same iommu_table (hardware IOMMU table) attached
> to the same LIOBN; we do not remove duplicates though as
> iommu_table_ops::exchange not just update a TCE entry (which is
> shared among IOMMU groups) but also invalidates the TCE cache
> (one per IOMMU group).
> 
> This advertises the new KVM_CAP_SPAPR_TCE_VFIO capability to the user
> space.
> 
> This adds real mode version of WARN_ON_ONCE() as the generic version
> causes problems with rcu_sched. Since we testing what vmalloc_to_phys()
> returns in the code, this also adds a check for already existing
> vmalloc_to_phys() call in kvmppc_rm_h_put_tce_indirect().
> 
> This finally makes use of vfio_external_user_iommu_id() which was
> introduced quite some time ago and was considered for removal.
> 
> Tests show that this patch increases transmission speed from 220MB/s
> to 750..1020MB/s on 10Gb network (Chelsea CXGB3 10Gb ethernet card).
> 
> Signed-off-by: Alexey Kardashevskiy 

Reviewed-by: David Gibson 

> ---
> Changes:
> v8:
> * changed all (!pua) checks to return H_TOO_HARD as ioctl() is supposed
> to handle them
> * changed vmalloc_to_phys() callers to return H_HARDWARE
> * changed real mode iommu_tce_xchg_rm() callers to return H_TOO_HARD
> and added a comment about this in the code
> * changed virtual mode iommu_tce_xchg() callers to return H_HARDWARE
> and do WARN_ON
> * added WARN_ON_ONCE_RM(!rmap) in kvmppc_rm_h_put_tce_indirect() to
> have all vmalloc_to_phys() callsites covered
> 
> v7:
> * added realmode-friendly WARN_ON_ONCE_RM
> 
> v6:
> * changed handling of errors returned by kvmppc_(rm_)tce_iommu_(un)map()
> * moved kvmppc_gpa_to_ua() to TCE validation
> 
> v5:
> * changed error codes in multiple places
> * added bunch of WARN_ON() in places which should not really happen
> * adde a check that an iommu table is not attached already to LIOBN
> * dropped explicit calls to iommu_tce_clear_param_check/
> iommu_tce_put_param_check as kvmppc_tce_validate/kvmppc_ioba_validate
> call them anyway (since the previous patch)
> * if we fail to update a hardware IOMMU table for unexpected reason,
> this just clears the entry
> 
> v4:
> * added note to the commit log about allowing multiple updates of
> the same IOMMU table;
> * instead of checking for if any memory was preregistered, this
> returns H_TOO_HARD if a specific page was not;
> * fixed comments from v3 about error handling in many places;
> * simplified TCE handlers and merged IOMMU parts inline - for example,
> there used to be kvmppc_h_put_tce_iommu(), now it is merged into
> kvmppc_h_put_tce(); this allows to check IOBA boundaries against
> the first attached table only (makes the code simpler);
> 
> v3:
> * simplified not to use VFIO group notifiers
> * reworked cleanup, should be 

[PATCH kernel v8 10/10] KVM: PPC: VFIO: Add in-kernel acceleration for VFIO

[Alexey Kardashevskiy]

This allows the host kernel to handle H_PUT_TCE, H_PUT_TCE_INDIRECT
and H_STUFF_TCE requests targeted an IOMMU TCE table used for VFIO
without passing them to user space which saves time on switching
to user space and back.

This adds H_PUT_TCE/H_PUT_TCE_INDIRECT/H_STUFF_TCE handlers to KVM.
KVM tries to handle a TCE request in the real mode, if failed
it passes the request to the virtual mode to complete the operation.
If it a virtual mode handler fails, the request is passed to
the user space; this is not expected to happen though.

To avoid dealing with page use counters (which is tricky in real mode),
this only accelerates SPAPR TCE IOMMU v2 clients which are required
to pre-register the userspace memory. The very first TCE request will
be handled in the VFIO SPAPR TCE driver anyway as the userspace view
of the TCE table (iommu_table::it_userspace) is not allocated till
the very first mapping happens and we cannot call vmalloc in real mode.

If we fail to update a hardware IOMMU table unexpected reason, we just
clear it and move on as there is nothing really we can do about it -
for example, if we hot plug a VFIO device to a guest, existing TCE tables
will be mirrored automatically to the hardware and there is no interface
to report to the guest about possible failures.

This adds new attribute - KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE - to
the VFIO KVM device. It takes a VFIO group fd and SPAPR TCE table fd
and associates a physical IOMMU table with the SPAPR TCE table (which
is a guest view of the hardware IOMMU table). The iommu_table object
is cached and referenced so we do not have to look up for it in real mode.

This does not implement the UNSET counterpart as there is no use for it -
once the acceleration is enabled, the existing userspace won't
disable it unless a VFIO container is destroyed; this adds necessary
cleanup to the KVM_DEV_VFIO_GROUP_DEL handler.

As this creates a descriptor per IOMMU table-LIOBN couple (called
kvmppc_spapr_tce_iommu_table), it is possible to have several
descriptors with the same iommu_table (hardware IOMMU table) attached
to the same LIOBN; we do not remove duplicates though as
iommu_table_ops::exchange not just update a TCE entry (which is
shared among IOMMU groups) but also invalidates the TCE cache
(one per IOMMU group).

This advertises the new KVM_CAP_SPAPR_TCE_VFIO capability to the user
space.

This adds real mode version of WARN_ON_ONCE() as the generic version
causes problems with rcu_sched. Since we testing what vmalloc_to_phys()
returns in the code, this also adds a check for already existing
vmalloc_to_phys() call in kvmppc_rm_h_put_tce_indirect().

This finally makes use of vfio_external_user_iommu_id() which was
introduced quite some time ago and was considered for removal.

Tests show that this patch increases transmission speed from 220MB/s
to 750..1020MB/s on 10Gb network (Chelsea CXGB3 10Gb ethernet card).

Signed-off-by: Alexey Kardashevskiy 
---
Changes:
v8:
* changed all (!pua) checks to return H_TOO_HARD as ioctl() is supposed
to handle them
* changed vmalloc_to_phys() callers to return H_HARDWARE
* changed real mode iommu_tce_xchg_rm() callers to return H_TOO_HARD
and added a comment about this in the code
* changed virtual mode iommu_tce_xchg() callers to return H_HARDWARE
and do WARN_ON
* added WARN_ON_ONCE_RM(!rmap) in kvmppc_rm_h_put_tce_indirect() to
have all vmalloc_to_phys() callsites covered

v7:
* added realmode-friendly WARN_ON_ONCE_RM

v6:
* changed handling of errors returned by kvmppc_(rm_)tce_iommu_(un)map()
* moved kvmppc_gpa_to_ua() to TCE validation

v5:
* changed error codes in multiple places
* added bunch of WARN_ON() in places which should not really happen
* adde a check that an iommu table is not attached already to LIOBN
* dropped explicit calls to iommu_tce_clear_param_check/
iommu_tce_put_param_check as kvmppc_tce_validate/kvmppc_ioba_validate
call them anyway (since the previous patch)
* if we fail to update a hardware IOMMU table for unexpected reason,
this just clears the entry

v4:
* added note to the commit log about allowing multiple updates of
the same IOMMU table;
* instead of checking for if any memory was preregistered, this
returns H_TOO_HARD if a specific page was not;
* fixed comments from v3 about error handling in many places;
* simplified TCE handlers and merged IOMMU parts inline - for example,
there used to be kvmppc_h_put_tce_iommu(), now it is merged into
kvmppc_h_put_tce(); this allows to check IOBA boundaries against
the first attached table only (makes the code simpler);

v3:
* simplified not to use VFIO group notifiers
* reworked cleanup, should be cleaner/simpler now

v2:
* reworked to use new VFIO notifiers
* now same iommu_table may appear in the list several times, to be fixed later
---
 Documentation/virtual/kvm/devices/vfio.txt |  22 +-
 arch/powerpc/include/asm/kvm_host.h|   8 +
 arch/powerpc/include/asm/kvm_ppc.h |   4 +
 include/uapi/linux/kvm.h