Re: [RFC v6 00/10] vfio-pci: Allow to mmap sub-page MMIO BARs and MSI-X table

[Yongji Xie <xyjxie@linux.vnet.ibm.com>]

On 2016/4/27 0:40, Alex Williamson wrote:

> On Mon, 25 Apr 2016 18:05:53 +0800
> Yongji Xie <xyjxie@linux.vnet.ibm.com> wrote:
>
>> Hi Alex,
>>
>> Any comment?
> TBH, I shuffled this to the bottom of the review pile because you're
> depending on a patch series for ARM MSI mapping that's still very much
> in flux.  You've really got 3 or 4 separate patch series here that
> should be separated so they can be sent as non-RFC and you can start
> making progress.  For instance, patches 1-4 are PCI-core enabling
> PAGE_SIZE aligned BARs, patch 5 discovers PAGE_SIZE aligned BARs and
> enables mmapping them through vfio.  Now that you're using shadow
> resources to attempt to reserve the remainder of the page in patch 5,
> doesn't that make it independent of patches 1-4?  These could be sent
> as separate series in parallel.  Patches 6-9 are another separate
> series, but here you start to depend on the changes happening with ARM
> MSI mapping to determine whether we have real interrupt isolation. Once
> that gets settled, patch 10 becomes a much less controversial follow-on
> patch.  Thanks,
>
> Alex

That's a really good idea! Thank you!

Regards,
Yongji

>> On 2016/4/18 18:53, Yongji Xie wrote:
>>> Current vfio-pci implementation disallows to mmap
>>> sub-page(size < PAGE_SIZE) MMIO BARs and MSI-X table. This is because
>>> sub-page BARs' mmio page may be shared with other BARs and MSI-X table
>>> should not be accessed directly from the guest for security reasons.
>>>
>>> But it will easily cause some performance issues for mmio accesses
>>> in guest when vfio passthrough sub-page BARs or BARs containing MSI-X
>>> table on PPC64 platform. This is because PAGE_SIZE is 64KB by default
>>> on PPC64 platform and the big page may easily hit the sub-page MMIO
>>> BARs' unmmapping and cause the unmmaping of the mmio page which
>>> MSI-X table locate in, which lead to mmio emulation in host.
>>>
>>> For sub-page MMIO BARs' unmmapping, this patchset modifies
>>> resource_alignment kernel parameter to enforce the alignment of all
>>> MMIO BARs to be at least PAGE_SZIE so that sub-page BAR's mmio page
>>> will not be shared with other BARs. And we also add shadow resources
>>> to the vfio device and put them into the holes of mmio pages in case
>>> that hot-add device's BARs are assigned into the holes. Then we can
>>> mmap sub-page MMIO BARs safely.
>>>
>>> For MSI-X table's unmmapping, we think MSI-X table is safe to access
>>> directly from userspace if hardware supports the capability of
>>> interrupt remapping which can ensure that a given pci device can
>>> only shoot the MSIs assigned for it. But the implenmentation of
>>> this capability is arch-independent. To have a universal way
>>> to test this capability on PCI side for different archs, we introduce
>>> a new bus_flags PCI_BUS_FLAGS_MSI_REMAP.
>>>
>>> With this patchset applied, we can get almost 100% improvement on
>>> performance for small block 4k random read when we passthrough a FC
>>> HBA containing sub-page BARs and MSI-X BARs to guest on PPC64 in
>>> our test.
>>>
>>> The patch 8 are based on the proposed patchset[2].
>>>
>>> Changelog v6:
>>> - Rebase on vfio/next with patchset[2] applied
>>> - Fix some bugs of v5
>>> - Add three patches to make PCI_BUS_FLAGS_MSI_REMAP as
>>>     a universal flag to test IRQ remapping
>>>
>>> Changelog v5:
>>> - Rebase on vfio/next
>>> - Change the order of patch 1,2,3
>>> - Move the warning "resource_alignment will not work with
>>>     PCI_PROBE_ONLY set" from documentation to kernel log
>>> - Remove IORESOURCE_WINDOW
>>> - Add description for parameter "resize"
>>> - Add PCIBIOS_MIN_ALIGNMENT to force all MMIO BARs to
>>>     get minimum alignment
>>> - Add shadow resources to make sure sub-page BAR's mmio
>>>     page will not be shared with hot-add BARs.
>>> - Add a new bit to pci_bus_flags to indicate the capbility
>>>     of interrupt remapping on PPC64
>>> - Remove IOMMU_CAP_INTR_REMAP on PPC64
>>> - Add a property msi_remap to vfio_pci_device to cache the
>>>     capbility of interrupt remapping
>>>
>>> Changelog v4:
>>> - Rebase on v4.5-rc6 with patchset[1] applied.
>>> - Remove resource_page_aligned kernel parameter
>>> - Fix some problems with resource_alignment kernel parameter
>>> - Modify resource_alignment kernel parameter to support multiple
>>>     devices.
>>> - Remove host bridge attribute: msi_filtered
>>> - Use IOMMU_CAP_INTR_REMAP to check if MSI-X table can be mmapped
>>> - Add IOMMU_CAP_INTR_REMAP for IODA host bridge on PPC64 platform
>>>
>>> Changelog v3:
>>> - Rebase on new linux kernel mainline with the patchset[1] applied.
>>> - Add a function to check whether PCI BARs'mmio page is shared with
>>>     other BARs.
>>> - Add a host bridge attribute to indicate PCI host bridge support
>>>     filtering of MSIs.
>>> - Use the new host bridge attribute to check if MSI-X table can
>>>     be mmapped instead of CONFIG_EEH.
>>> - Remove Kconfig option VFIO_PCI_MMAP_MSIX
>>>
>>> Changelog v2:
>>> - Rebase on v4.4-rc6 with the patchset[1] applied.
>>> - Use kernel parameter to enforce all MMIO BARs to be page aligned
>>>     on PCI core code instead of doing it on PPC64 arch code.
>>> - Remove flags: VFIO_DEVICE_FLAGS_PCI_PAGE_ALIGNED
>>>
>>> [1] http://www.spinics.net/lists/kvm/msg127812.html
>>> [2] http://www.spinics.net/lists/kvm/msg130256.html
>>>
>>> Yongji Xie (10):
>>>     PCI: Ignore resource_alignment if PCI_PROBE_ONLY was set
>>>     PCI: Do not Use IORESOURCE_STARTALIGN to identify bridge resources
>>>     PCI: Add a new option for resource_alignment to reassign alignment
>>>     PCI: Add support for enforcing all MMIO BARs to be page aligned
>>>     vfio-pci: Allow to mmap sub-page MMIO BARs if the mmio page is exclusive
>>>     PCI: Add a new PCI_BUS_FLAGS_MSI_REMAP flag
>>>     iommu: Set PCI_BUS_FLAGS_MSI_REMAP if IOMMU have capability of IRQ remapping
>>>     PCI: Set PCI_BUS_FLAGS_MSI_REMAP if MSI controller supports IRQ remapping
>>>     pci-ioda: Set PCI_BUS_FLAGS_MSI_REMAP for IODA host bridge
>>>     vfio-pci: Allow to mmap MSI-X table if interrupt remapping is supported
>>>
>>>    Documentation/kernel-parameters.txt       |    7 +-
>>>    arch/powerpc/include/asm/pci.h            |    2 +
>>>    arch/powerpc/platforms/powernv/pci-ioda.c |    8 +++
>>>    drivers/iommu/iommu.c                     |   15 +++++
>>>    drivers/pci/msi.c                         |   12 ++++
>>>    drivers/pci/pci.c                         |  105 +++++++++++++++++++++++------
>>>    drivers/pci/probe.c                       |    3 +
>>>    drivers/pci/setup-bus.c                   |    9 ++-
>>>    drivers/vfio/pci/vfio_pci.c               |   65 +++++++++++++++---
>>>    drivers/vfio/pci/vfio_pci_private.h       |    8 +++
>>>    drivers/vfio/pci/vfio_pci_rdwr.c          |    3 +-
>>>    include/linux/msi.h                       |    6 +-
>>>    include/linux/pci.h                       |    1 +
>>>    13 files changed, 208 insertions(+), 36 deletions(-)
>>>   
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