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Re: [PATCH kernel 0/3 REPOST] vfio-pci: Add support for mmapping MSI-X table

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  Re: [PATCH kernel 0/3 REPOST] vfio-pci: Add support for mmapping  MSI-X table Alex Williamson <alex.williamson@redhat.com> - 2017-06-22 23:20 +0200
    Re: [PATCH kernel 0/3 REPOST] vfio-pci: Add support for mmapping  MSI-X table Alexey Kardashevskiy <aik@ozlabs.ru> - 2017-06-23 07:10 +0200
      Re: [PATCH kernel 0/3 REPOST] vfio-pci: Add support for mmapping  MSI-X table Alex Williamson <alex.williamson@redhat.com> - 2017-06-23 17:20 +0200
        Re: [PATCH kernel 0/3 REPOST] vfio-pci: Add support for mmapping  MSI-X table Alexey Kardashevskiy <aik@ozlabs.ru> - 2017-06-28 09:30 +0200
          Re: [PATCH kernel 0/3 REPOST] vfio-pci: Add support for mmapping  MSI-X table Alex Williamson <alex.williamson@redhat.com> - 2017-06-29 22:10 +0200

#1673056 — Re: [PATCH kernel 0/3 REPOST] vfio-pci: Add support for mmapping MSI-X table

On Thu, 15 Jun 2017 15:48:42 +1000
Alexey Kardashevskiy <aik@ozlabs.ru> wrote:

> Here is a patchset which Yongji was working on before
> leaving IBM LTC. Since we still want to have this functionality
> in the kernel (DPDK is the first user), here is a rebase
> on the current upstream.
> 
> 
> Current vfio-pci implementation disallows to mmap the page
> containing MSI-X table in case that users can write directly
> to MSI-X table and generate an incorrect MSIs.
> 
> However, this will cause some performance issue when there
> are some critical device registers in the same page as the
> MSI-X table. We have to handle the mmio access to these
> registers in QEMU emulation rather than in guest.
> 
> To solve this issue, this series allows to expose MSI-X table
> to userspace when hardware enables the capability of interrupt
> remapping which can ensure that a given PCI device can only
> shoot the MSIs assigned for it. And we introduce a new bus_flags
> PCI_BUS_FLAGS_MSI_REMAP to test this capability on PCI side
> for different archs.
> 
> The patch 3 are based on the proposed patchset[1].
> 
> Changelog
> v3:
> - rebased on the current upstream

There's something not forthcoming here, the last version I see from
Yongji is this one:

https://lists.linuxfoundation.org/pipermail/iommu/2016-June/017245.html

Which was a 6-patch series where patches 2-4 tried to apply
PCI_BUS_FLAGS_MSI_REMAP for cases that supported other platforms.  That
doesn't exist here, so it's not simply a rebase.  Patch 1/ seems to
equate this new flag to the IOMMU capability IOMMU_CAP_INTR_REMAP, but
nothing is done here to match them together.  That patch also mentions
the work Eric has done for similar features on ARM, but again those
patches are dropped.  It seems like an incomplete feature now.  Thanks,

Alex

> v2:
> - Make the commit log more clear
> - Replace pci_bus_check_msi_remapping() with pci_bus_msi_isolated()
>   so that we could clearly know what the function does
> - Set PCI_BUS_FLAGS_MSI_REMAP in pci_create_root_bus() instead
>   of iommu_bus_notifier()
> - Reserve VFIO_REGION_INFO_FLAG_CAPS when we allow to mmap MSI-X
>   table so that we can know whether we allow to mmap MSI-X table
>   in QEMU
> 
> [1] https://www.mail-archive.com/linux-kernel%40vger.kernel.org/msg1138820.html
> 
> 
> This is based on sha1
> 63f700aab4c1 Linus Torvalds "Merge tag 'xtensa-20170612' of git://github.com/jcmvbkbc/linux-xtensa".
> 
> Please comment. Thanks.
> 
> 
> 
> Yongji Xie (3):
>   PCI: Add a new PCI_BUS_FLAGS_MSI_REMAP flag
>   pci-ioda: Set PCI_BUS_FLAGS_MSI_REMAP for IODA host bridge
>   vfio-pci: Allow to expose MSI-X table to userspace if interrupt
>     remapping is enabled
> 
>  include/linux/pci.h                       |  1 +
>  arch/powerpc/platforms/powernv/pci-ioda.c |  8 ++++++++
>  drivers/vfio/pci/vfio_pci.c               | 18 +++++++++++++++---
>  drivers/vfio/pci/vfio_pci_rdwr.c          |  3 ++-
>  4 files changed, 26 insertions(+), 4 deletions(-)
> 

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#1673250

On 23/06/17 07:11, Alex Williamson wrote:
> On Thu, 15 Jun 2017 15:48:42 +1000
> Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
> 
>> Here is a patchset which Yongji was working on before
>> leaving IBM LTC. Since we still want to have this functionality
>> in the kernel (DPDK is the first user), here is a rebase
>> on the current upstream.
>>
>>
>> Current vfio-pci implementation disallows to mmap the page
>> containing MSI-X table in case that users can write directly
>> to MSI-X table and generate an incorrect MSIs.
>>
>> However, this will cause some performance issue when there
>> are some critical device registers in the same page as the
>> MSI-X table. We have to handle the mmio access to these
>> registers in QEMU emulation rather than in guest.
>>
>> To solve this issue, this series allows to expose MSI-X table
>> to userspace when hardware enables the capability of interrupt
>> remapping which can ensure that a given PCI device can only
>> shoot the MSIs assigned for it. And we introduce a new bus_flags
>> PCI_BUS_FLAGS_MSI_REMAP to test this capability on PCI side
>> for different archs.
>>
>> The patch 3 are based on the proposed patchset[1].
>>
>> Changelog
>> v3:
>> - rebased on the current upstream
> 
> There's something not forthcoming here, the last version I see from
> Yongji is this one:
> 
> https://lists.linuxfoundation.org/pipermail/iommu/2016-June/017245.html
> 
> Which was a 6-patch series where patches 2-4 tried to apply
> PCI_BUS_FLAGS_MSI_REMAP for cases that supported other platforms.  That
> doesn't exist here, so it's not simply a rebase.  Patch 1/ seems to
> equate this new flag to the IOMMU capability IOMMU_CAP_INTR_REMAP, but
> nothing is done here to match them together.  That patch also mentions
> the work Eric has done for similar features on ARM, but again those
> patches are dropped.  It seems like an incomplete feature now.  Thanks,


Thanks! I suspected this is not the latest but could not find anything
better than we use internally for tests, and I could not reach Yongji for
comments whether this was the latest update.

As I am reading the patches, I notice that the "msi remap" term is used all
over the place. While this remapping capability may be the case for x86/arm
(and therefore the IOMMU_CAP_INTR_REMAP flag makes sense), powernv does not
do remapping but provides hardware isolation. When we are allowing MSIX BAR
mapping to the userspace - the isolation is what we really care about. Will
it make sense to rename PCI_BUS_FLAGS_MSI_REMAP to
PCI_BUS_FLAGS_MSI_ISOLATED ?

Another thing - the patchset enables PCI_BUS_FLAGS_MSI_REMAP when IOMMU
just advertises IOMMU_CAP_INTR_REMAP, not necessarily uses it, should the
patchset actually look at something like irq_remapping_enabled in
drivers/iommu/amd_iommu.c instead?



> 
> Alex
> 
>> v2:
>> - Make the commit log more clear
>> - Replace pci_bus_check_msi_remapping() with pci_bus_msi_isolated()
>>   so that we could clearly know what the function does
>> - Set PCI_BUS_FLAGS_MSI_REMAP in pci_create_root_bus() instead
>>   of iommu_bus_notifier()
>> - Reserve VFIO_REGION_INFO_FLAG_CAPS when we allow to mmap MSI-X
>>   table so that we can know whether we allow to mmap MSI-X table
>>   in QEMU
>>
>> [1] https://www.mail-archive.com/linux-kernel%40vger.kernel.org/msg1138820.html
>>
>>
>> This is based on sha1
>> 63f700aab4c1 Linus Torvalds "Merge tag 'xtensa-20170612' of git://github.com/jcmvbkbc/linux-xtensa".
>>
>> Please comment. Thanks.
>>
>>
>>
>> Yongji Xie (3):
>>   PCI: Add a new PCI_BUS_FLAGS_MSI_REMAP flag
>>   pci-ioda: Set PCI_BUS_FLAGS_MSI_REMAP for IODA host bridge
>>   vfio-pci: Allow to expose MSI-X table to userspace if interrupt
>>     remapping is enabled
>>
>>  include/linux/pci.h                       |  1 +
>>  arch/powerpc/platforms/powernv/pci-ioda.c |  8 ++++++++
>>  drivers/vfio/pci/vfio_pci.c               | 18 +++++++++++++++---
>>  drivers/vfio/pci/vfio_pci_rdwr.c          |  3 ++-
>>  4 files changed, 26 insertions(+), 4 deletions(-)
>>
> 


-- 
Alexey

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#1673627

On Fri, 23 Jun 2017 15:06:37 +1000
Alexey Kardashevskiy <aik@ozlabs.ru> wrote:

> On 23/06/17 07:11, Alex Williamson wrote:
> > On Thu, 15 Jun 2017 15:48:42 +1000
> > Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
> >   
> >> Here is a patchset which Yongji was working on before
> >> leaving IBM LTC. Since we still want to have this functionality
> >> in the kernel (DPDK is the first user), here is a rebase
> >> on the current upstream.
> >>
> >>
> >> Current vfio-pci implementation disallows to mmap the page
> >> containing MSI-X table in case that users can write directly
> >> to MSI-X table and generate an incorrect MSIs.
> >>
> >> However, this will cause some performance issue when there
> >> are some critical device registers in the same page as the
> >> MSI-X table. We have to handle the mmio access to these
> >> registers in QEMU emulation rather than in guest.
> >>
> >> To solve this issue, this series allows to expose MSI-X table
> >> to userspace when hardware enables the capability of interrupt
> >> remapping which can ensure that a given PCI device can only
> >> shoot the MSIs assigned for it. And we introduce a new bus_flags
> >> PCI_BUS_FLAGS_MSI_REMAP to test this capability on PCI side
> >> for different archs.
> >>
> >> The patch 3 are based on the proposed patchset[1].
> >>
> >> Changelog
> >> v3:
> >> - rebased on the current upstream  
> > 
> > There's something not forthcoming here, the last version I see from
> > Yongji is this one:
> > 
> > https://lists.linuxfoundation.org/pipermail/iommu/2016-June/017245.html
> > 
> > Which was a 6-patch series where patches 2-4 tried to apply
> > PCI_BUS_FLAGS_MSI_REMAP for cases that supported other platforms.  That
> > doesn't exist here, so it's not simply a rebase.  Patch 1/ seems to
> > equate this new flag to the IOMMU capability IOMMU_CAP_INTR_REMAP, but
> > nothing is done here to match them together.  That patch also mentions
> > the work Eric has done for similar features on ARM, but again those
> > patches are dropped.  It seems like an incomplete feature now.  Thanks,  
> 
> 
> Thanks! I suspected this is not the latest but could not find anything
> better than we use internally for tests, and I could not reach Yongji for
> comments whether this was the latest update.
> 
> As I am reading the patches, I notice that the "msi remap" term is used all
> over the place. While this remapping capability may be the case for x86/arm
> (and therefore the IOMMU_CAP_INTR_REMAP flag makes sense), powernv does not
> do remapping but provides hardware isolation. When we are allowing MSIX BAR
> mapping to the userspace - the isolation is what we really care about. Will
> it make sense to rename PCI_BUS_FLAGS_MSI_REMAP to
> PCI_BUS_FLAGS_MSI_ISOLATED ?

I don't have a strong opinion either way, so long as it's fully
described what the flag indicates.

> Another thing - the patchset enables PCI_BUS_FLAGS_MSI_REMAP when IOMMU
> just advertises IOMMU_CAP_INTR_REMAP, not necessarily uses it, should the
> patchset actually look at something like irq_remapping_enabled in
> drivers/iommu/amd_iommu.c instead?

Interrupt remapping being enabled is implicit in IOMMU_CAP_INTR_REMAP,
neither intel or amd iommu export the capability unless enabled.
Nobody cares if it's supported but not enabled.  Thanks,

Alex

> >> v2:
> >> - Make the commit log more clear
> >> - Replace pci_bus_check_msi_remapping() with pci_bus_msi_isolated()
> >>   so that we could clearly know what the function does
> >> - Set PCI_BUS_FLAGS_MSI_REMAP in pci_create_root_bus() instead
> >>   of iommu_bus_notifier()
> >> - Reserve VFIO_REGION_INFO_FLAG_CAPS when we allow to mmap MSI-X
> >>   table so that we can know whether we allow to mmap MSI-X table
> >>   in QEMU
> >>
> >> [1] https://www.mail-archive.com/linux-kernel%40vger.kernel.org/msg1138820.html
> >>
> >>
> >> This is based on sha1
> >> 63f700aab4c1 Linus Torvalds "Merge tag 'xtensa-20170612' of git://github.com/jcmvbkbc/linux-xtensa".
> >>
> >> Please comment. Thanks.
> >>
> >>
> >>
> >> Yongji Xie (3):
> >>   PCI: Add a new PCI_BUS_FLAGS_MSI_REMAP flag
> >>   pci-ioda: Set PCI_BUS_FLAGS_MSI_REMAP for IODA host bridge
> >>   vfio-pci: Allow to expose MSI-X table to userspace if interrupt
> >>     remapping is enabled
> >>
> >>  include/linux/pci.h                       |  1 +
> >>  arch/powerpc/platforms/powernv/pci-ioda.c |  8 ++++++++
> >>  drivers/vfio/pci/vfio_pci.c               | 18 +++++++++++++++---
> >>  drivers/vfio/pci/vfio_pci_rdwr.c          |  3 ++-
> >>  4 files changed, 26 insertions(+), 4 deletions(-)
> >>  
> >   
> 
> 

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#1676420

On 24/06/17 01:17, Alex Williamson wrote:
> On Fri, 23 Jun 2017 15:06:37 +1000
> Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
> 
>> On 23/06/17 07:11, Alex Williamson wrote:
>>> On Thu, 15 Jun 2017 15:48:42 +1000
>>> Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
>>>   
>>>> Here is a patchset which Yongji was working on before
>>>> leaving IBM LTC. Since we still want to have this functionality
>>>> in the kernel (DPDK is the first user), here is a rebase
>>>> on the current upstream.
>>>>
>>>>
>>>> Current vfio-pci implementation disallows to mmap the page
>>>> containing MSI-X table in case that users can write directly
>>>> to MSI-X table and generate an incorrect MSIs.
>>>>
>>>> However, this will cause some performance issue when there
>>>> are some critical device registers in the same page as the
>>>> MSI-X table. We have to handle the mmio access to these
>>>> registers in QEMU emulation rather than in guest.
>>>>
>>>> To solve this issue, this series allows to expose MSI-X table
>>>> to userspace when hardware enables the capability of interrupt
>>>> remapping which can ensure that a given PCI device can only
>>>> shoot the MSIs assigned for it. And we introduce a new bus_flags
>>>> PCI_BUS_FLAGS_MSI_REMAP to test this capability on PCI side
>>>> for different archs.
>>>>
>>>> The patch 3 are based on the proposed patchset[1].
>>>>
>>>> Changelog
>>>> v3:
>>>> - rebased on the current upstream  
>>>
>>> There's something not forthcoming here, the last version I see from
>>> Yongji is this one:
>>>
>>> https://lists.linuxfoundation.org/pipermail/iommu/2016-June/017245.html
>>>
>>> Which was a 6-patch series where patches 2-4 tried to apply
>>> PCI_BUS_FLAGS_MSI_REMAP for cases that supported other platforms.  That
>>> doesn't exist here, so it's not simply a rebase.  Patch 1/ seems to
>>> equate this new flag to the IOMMU capability IOMMU_CAP_INTR_REMAP, but
>>> nothing is done here to match them together.  That patch also mentions
>>> the work Eric has done for similar features on ARM, but again those
>>> patches are dropped.  It seems like an incomplete feature now.  Thanks,  
>>
>>
>> Thanks! I suspected this is not the latest but could not find anything
>> better than we use internally for tests, and I could not reach Yongji for
>> comments whether this was the latest update.
>>
>> As I am reading the patches, I notice that the "msi remap" term is used all
>> over the place. While this remapping capability may be the case for x86/arm
>> (and therefore the IOMMU_CAP_INTR_REMAP flag makes sense), powernv does not
>> do remapping but provides hardware isolation. When we are allowing MSIX BAR
>> mapping to the userspace - the isolation is what we really care about. Will
>> it make sense to rename PCI_BUS_FLAGS_MSI_REMAP to
>> PCI_BUS_FLAGS_MSI_ISOLATED ?
> 
> I don't have a strong opinion either way, so long as it's fully
> described what the flag indicates.
> 
>> Another thing - the patchset enables PCI_BUS_FLAGS_MSI_REMAP when IOMMU
>> just advertises IOMMU_CAP_INTR_REMAP, not necessarily uses it, should the
>> patchset actually look at something like irq_remapping_enabled in
>> drivers/iommu/amd_iommu.c instead?
> 
> Interrupt remapping being enabled is implicit in IOMMU_CAP_INTR_REMAP,
> neither intel or amd iommu export the capability unless enabled.
> Nobody cares if it's supported but not enabled.  Thanks,


As I am reading the current drivers/vfio/vfio_iommu_type1.c, it feels like
MSIX BAR mappings can always be allowed for the type1 IOMMU as
vfio_iommu_type1_attach_group() performs this check:

msi_remap = resv_msi ? irq_domain_check_msi_remap() :
    iommu_capable(bus, IOMMU_CAP_INTR_REMAP);

and simply does not proceed if MSI remap is not supported. Is that correct
or I miss something here? Thanks.




-- 
Alexey

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#1678149

On Wed, 28 Jun 2017 17:27:32 +1000
Alexey Kardashevskiy <aik@ozlabs.ru> wrote:

> On 24/06/17 01:17, Alex Williamson wrote:
> > On Fri, 23 Jun 2017 15:06:37 +1000
> > Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
> >   
> >> On 23/06/17 07:11, Alex Williamson wrote:  
> >>> On Thu, 15 Jun 2017 15:48:42 +1000
> >>> Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
> >>>     
> >>>> Here is a patchset which Yongji was working on before
> >>>> leaving IBM LTC. Since we still want to have this functionality
> >>>> in the kernel (DPDK is the first user), here is a rebase
> >>>> on the current upstream.
> >>>>
> >>>>
> >>>> Current vfio-pci implementation disallows to mmap the page
> >>>> containing MSI-X table in case that users can write directly
> >>>> to MSI-X table and generate an incorrect MSIs.
> >>>>
> >>>> However, this will cause some performance issue when there
> >>>> are some critical device registers in the same page as the
> >>>> MSI-X table. We have to handle the mmio access to these
> >>>> registers in QEMU emulation rather than in guest.
> >>>>
> >>>> To solve this issue, this series allows to expose MSI-X table
> >>>> to userspace when hardware enables the capability of interrupt
> >>>> remapping which can ensure that a given PCI device can only
> >>>> shoot the MSIs assigned for it. And we introduce a new bus_flags
> >>>> PCI_BUS_FLAGS_MSI_REMAP to test this capability on PCI side
> >>>> for different archs.
> >>>>
> >>>> The patch 3 are based on the proposed patchset[1].
> >>>>
> >>>> Changelog
> >>>> v3:
> >>>> - rebased on the current upstream    
> >>>
> >>> There's something not forthcoming here, the last version I see from
> >>> Yongji is this one:
> >>>
> >>> https://lists.linuxfoundation.org/pipermail/iommu/2016-June/017245.html
> >>>
> >>> Which was a 6-patch series where patches 2-4 tried to apply
> >>> PCI_BUS_FLAGS_MSI_REMAP for cases that supported other platforms.  That
> >>> doesn't exist here, so it's not simply a rebase.  Patch 1/ seems to
> >>> equate this new flag to the IOMMU capability IOMMU_CAP_INTR_REMAP, but
> >>> nothing is done here to match them together.  That patch also mentions
> >>> the work Eric has done for similar features on ARM, but again those
> >>> patches are dropped.  It seems like an incomplete feature now.  Thanks,    
> >>
> >>
> >> Thanks! I suspected this is not the latest but could not find anything
> >> better than we use internally for tests, and I could not reach Yongji for
> >> comments whether this was the latest update.
> >>
> >> As I am reading the patches, I notice that the "msi remap" term is used all
> >> over the place. While this remapping capability may be the case for x86/arm
> >> (and therefore the IOMMU_CAP_INTR_REMAP flag makes sense), powernv does not
> >> do remapping but provides hardware isolation. When we are allowing MSIX BAR
> >> mapping to the userspace - the isolation is what we really care about. Will
> >> it make sense to rename PCI_BUS_FLAGS_MSI_REMAP to
> >> PCI_BUS_FLAGS_MSI_ISOLATED ?  
> > 
> > I don't have a strong opinion either way, so long as it's fully
> > described what the flag indicates.
> >   
> >> Another thing - the patchset enables PCI_BUS_FLAGS_MSI_REMAP when IOMMU
> >> just advertises IOMMU_CAP_INTR_REMAP, not necessarily uses it, should the
> >> patchset actually look at something like irq_remapping_enabled in
> >> drivers/iommu/amd_iommu.c instead?  
> > 
> > Interrupt remapping being enabled is implicit in IOMMU_CAP_INTR_REMAP,
> > neither intel or amd iommu export the capability unless enabled.
> > Nobody cares if it's supported but not enabled.  Thanks,  
> 
> 
> As I am reading the current drivers/vfio/vfio_iommu_type1.c, it feels like
> MSIX BAR mappings can always be allowed for the type1 IOMMU as
> vfio_iommu_type1_attach_group() performs this check:
> 
> msi_remap = resv_msi ? irq_domain_check_msi_remap() :
>     iommu_capable(bus, IOMMU_CAP_INTR_REMAP);
> 
> and simply does not proceed if MSI remap is not supported. Is that correct
> or I miss something here? Thanks.

The MSI code in type1 has absolutely nothing to do with BAR mappings.
That's looking at how MSI is handled by the IOMMU, whether it needs a
reserved mapping area and whether MSI writes have source ID
validation.  Thanks,

Alex

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