Subject: Re: [RFC PATCH v4 0/7] vfio-pci: Allow to mmap sub-page MMIO BARs and
 MSI-X table
To: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-pci@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
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        alex.williamson@redhat.com, benh@kernel.crashing.org, paulus@samba.org,
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        zhong@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com
From: Yongji Xie <xyjxie@linux.vnet.ibm.com>
Message-ID: <56E93ACC.7080403@linux.vnet.ibm.com>
Date: Wed, 16 Mar 2016 18:51:56 +0800
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Ping.

On 2016/3/7 15:48, 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 these 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. Then we can mmap sub-page MMIO BARs
> in vfio-pci driver with the modified resource_alignment.
>
> For MSI-X table's unmmapping, we think MSI-X table is safe to access
> directly from userspace if PCI host bridge support filtering of MSIs
> which can ensure that a given pci device can only shoot the MSIs
> assigned for it. So we allow to mmap MSI-X table if
> IOMMU_CAP_INTR_REMAP was set. And we add IOMMU_CAP_INTR_REMAP for
> IODA host bridge on PPC64 platform.
>
> With this patchset applied, we can get almost 100% improvement on
> performance for mmio accesses when we passthrough sub-page BARs to guest
> in our test.
>
> The two vfio related patches(patch 5 and patch 6) are based on the
> proposed patchset[1].
>
> 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
> 		VFIO_DEVICE_FLAGS_PCI_MSIX_MMAP
> - Add a Kconfig option to support for mmapping MSI-X table.
>
> [1] http://www.spinics.net/lists/kvm/msg127812.html
>
> Yongji Xie (7):
>    PCI: Add a new option for resource_alignment to reassign alignment
>    PCI: Use IORESOURCE_WINDOW to identify bridge resources
>    PCI: Ignore resource_alignment if PCI_PROBE_ONLY was set
>    PCI: Modify resource_alignment to support multiple devices
>    vfio-pci: Allow to mmap sub-page MMIO BARs if the mmio page is exclusive
>    vfio-pci: Allow to mmap MSI-X table if IOMMU_CAP_INTR_REMAP was set
>    powerpc/powernv/pci-ioda: Add IOMMU_CAP_INTR_REMAP for IODA host bridge
>
>   Documentation/kernel-parameters.txt       |    9 ++-
>   arch/powerpc/platforms/powernv/pci-ioda.c |   17 ++++
>   drivers/pci/pci.c                         |  126 ++++++++++++++++++++++++-----
>   drivers/pci/probe.c                       |    3 +-
>   drivers/pci/setup-bus.c                   |   21 ++---
>   drivers/vfio/pci/vfio_pci.c               |   15 +++-
>   drivers/vfio/pci/vfio_pci_rdwr.c          |    4 +-
>   include/linux/pci.h                       |    4 +
>   8 files changed, 162 insertions(+), 37 deletions(-)
>