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Diffstat (limited to 'Documentation/vfio.txt')
| -rw-r--r-- | Documentation/vfio.txt | 31 |
1 files changed, 28 insertions, 3 deletions
diff --git a/Documentation/vfio.txt b/Documentation/vfio.txt index 4c746a7e717a..dcc37e109c68 100644 --- a/Documentation/vfio.txt +++ b/Documentation/vfio.txt @@ -289,10 +289,12 @@ PPC64 sPAPR implementation note This implementation has some specifics: -1) Only one IOMMU group per container is supported as an IOMMU group -represents the minimal entity which isolation can be guaranteed for and -groups are allocated statically, one per a Partitionable Endpoint (PE) +1) On older systems (POWER7 with P5IOC2/IODA1) only one IOMMU group per +container is supported as an IOMMU table is allocated at the boot time, +one table per a IOMMU group which is a Partitionable Endpoint (PE) (PE is often a PCI domain but not always). +Newer systems (POWER8 with IODA2) have improved hardware design which allows +to remove this limitation and have multiple IOMMU groups per a VFIO container. 2) The hardware supports so called DMA windows - the PCI address range within which DMA transfer is allowed, any attempt to access address space @@ -439,6 +441,29 @@ The code flow from the example above should be slightly changed: .... +5) There is v2 of SPAPR TCE IOMMU. It deprecates VFIO_IOMMU_ENABLE/ +VFIO_IOMMU_DISABLE and implements 2 new ioctls: +VFIO_IOMMU_SPAPR_REGISTER_MEMORY and VFIO_IOMMU_SPAPR_UNREGISTER_MEMORY +(which are unsupported in v1 IOMMU). + +PPC64 paravirtualized guests generate a lot of map/unmap requests, +and the handling of those includes pinning/unpinning pages and updating +mm::locked_vm counter to make sure we do not exceed the rlimit. +The v2 IOMMU splits accounting and pinning into separate operations: + +- VFIO_IOMMU_SPAPR_REGISTER_MEMORY/VFIO_IOMMU_SPAPR_UNREGISTER_MEMORY ioctls +receive a user space address and size of the block to be pinned. +Bisecting is not supported and VFIO_IOMMU_UNREGISTER_MEMORY is expected to +be called with the exact address and size used for registering +the memory block. The userspace is not expected to call these often. +The ranges are stored in a linked list in a VFIO container. + +- VFIO_IOMMU_MAP_DMA/VFIO_IOMMU_UNMAP_DMA ioctls only update the actual +IOMMU table and do not do pinning; instead these check that the userspace +address is from pre-registered range. + +This separation helps in optimizing DMA for guests. + ------------------------------------------------------------------------------- [1] VFIO was originally an acronym for "Virtual Function I/O" in its |