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 capbility of interrupt remapping which can ensure that a given pci device can only shoot the MSIs assigned for it. So it's safe to mmap MSI-X table if IOMMU_CAP_INTR_REMAP was set. But on PPC64, it's hard to use this existing flag to indicate the capbility because we never set/use iommu_ops. Now I'm trying to find a proper way to indicate that on PPC64. In this patchset, we add a new bit to pci_bus_flags to indicate that. But I'm not sure whether it's good enough. 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. 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 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: 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 bit to pci_bus_flags to indicate interrupt remapping 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/pci/pci.c | 107 +++++++++++++++++++++++------ drivers/pci/setup-bus.c | 10 ++- drivers/vfio/pci/vfio_pci.c | 67 +++++++++++++++--- drivers/vfio/pci/vfio_pci_private.h | 9 +++ drivers/vfio/pci/vfio_pci_rdwr.c | 2 +- include/linux/pci.h | 1 + 9 files changed, 178 insertions(+), 35 deletions(-) -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
