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

[Yongji Xie]

Hi Alex,

Any comment?

Thanks,
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(-)