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 adds a kernel parameter for PCI resource allocator to enforce the alignment of all MMIO BARs to be at least PAGE_SZIE and make it enabled by default on PPC64 platform 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 this parameter enabled. For MSI-X table's unmmapping, we think MSI-X table is safe to access directly from userspace with EEH mechanism enabled which can ensure that a given pci device can only shoot the MSIs assigned for its PE. So we add a Kconfig option to support for mmapping MSI-X table in vfio-pci driver if EEH is supported. 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 last two patches are based on the proposed patchset[1]. 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] https://lkml.org/lkml/2015/11/23/748 Yongji Xie (3): PCI: Add support for enforcing all MMIO BARs to be page aligned vfio-pci: Allow to mmap sub-page MMIO BARs if all MMIO BARs are page aligned vfio-pci: Allow to mmap MSI-X table if EEH is supported Documentation/kernel-parameters.txt | 4 ++++ arch/powerpc/include/asm/pci.h | 11 +++++++++++ drivers/pci/pci.c | 17 +++++++++++++++++ drivers/pci/pci.h | 7 ++++++- drivers/vfio/pci/Kconfig | 4 ++++ drivers/vfio/pci/vfio_pci.c | 13 ++++++++++--- include/linux/pci.h | 2 ++ 7 files changed, 54 insertions(+), 4 deletions(-) -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html