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(-) -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
