Hi Laszlo,
(5.3) All virtio driver code should treat VIRTIO_F_IOMMU_PLATFORM simply
in parallel with VIRTIO_F_VERSION_1, and don't act upon
VIRTIO_F_IOMMU_PLATFORM in any special shape or form. So basically this
is just my point (3) from above.
(5.4) There are three VIRTIO_DEVICE_PROTOCOL implementations in edk2:
- "OvmfPkg/VirtioPciDeviceDxe" binds legacy-only and transitional
virtio-pci devices, and offers virtio 0.9.5 semantics.
- "ArmVirtPkg/VirtioFdtDxe" (via "OvmfPkg/Library/VirtioMmioDeviceLib")
binds virtio-mmio devices, and offers virtio 0.9.5 semantics.
- "OvmfPkg/Virtio10Dxe" binds modern-only virtio-pci devices, and offers
virtio 1.0.0 semantics.
The first two drivers should implement the AllocateSharedPages() and
FreeSharedPages() member functions simply with the corresponding
MemoryAllocationLib functions (using BootServicesData type memory), and
implement the MapSharedPages() and UnmapSharedPages() member functions
as no-ops (return the input addresses transparently).
The third driver should implement all four new member functions by
respectively delegating the job to:
- EFI_PCI_IO_PROTOCOL.AllocateBuffer() -- with BootServicesData --
- EFI_PCI_IO_PROTOCOL.FreeBuffer()
- EFI_PCI_IO_PROTOCOL.Map() -- with BusMasterCommonBuffer64 --
- EFI_PCI_IO_PROTOCOL.Unmap()
I have working to implement patch per your recommendation. I assume you mean
map the buffers with EfiPciIoOperationBusMasterCommonBuffer [1]. If so, I see
one issue with SEV guest. When SEV is active, IOMMU driver uses a bounce buffer
to map host address to a device address. While creating bounce buffer we can map
it either for EfiPciIoOperationBusMasterRead or EfiPciIoOperationBusMasterWrite
Operation. If caller wants to map EfiPciIoOperationBusMasterCommonBuffer then it
must allocate the buffer using EFI_PCI_IO_PROTOCOL.AllocateBuffer() [2]
otherwise
we will fail to map. I see that PciRootBridgeIo.c has similar check when using
a bounce buffer for < 4GB use cases [3].
Do you see any issue if we use EfiPciIoOperationBusMasterRead or
EfiPciIoOperationBusMasterWrite
instead of EfiPciIoOperationBusMasterCommonBuffer ?
[1]
https://github.com/tianocore/edk2/blob/master/EdkCompatibilityPkg/Foundation/Efi/Protocol/PciIo/PciIo.h#L169
[2]
https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Bus/Pci/PciBusDxe/PciIo.c#L1082
[3]
https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Bus/Pci/PciHostBridgeDxe/PciRootBridgeIo.c#L1109
The EFI_PCI_IO_PROTOCOL implementation will delegate these calls to the
platform-specific PCI host bridge / root bridge driver, and *that*
driver in turn is allowed to talk to an IOMMU protocol (if any).
(This last step is already covered by the following edk2 commits:
- generally, c15da8eb3587 ("MdeModulePkg/PciHostBridge: Add IOMMU
support.", 2017-04-29),
- specifically for SEV in OVMF, c6ab9aecb71b ("OvmfPkg: update
PciHostBridgeDxe to use PlatformHasIoMmuLib", 2017-07-06).)
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