[dpdk-dev] [PATCH v8 0/3] fix issue with partial DMA unmap

Burakov, Anatoly anatoly.burakov at intel.com
Tue Feb 16 14:14:37 CET 2021

On 15-Jan-21 7:32 AM, Nithin Dabilpuram wrote:
> Partial DMA unmap is not supported by VFIO type1 IOMMU
> in Linux. Though the return value is zero, the returned
> DMA unmap size is not same as expected size.
> So add test case and fix to both heap triggered DMA
> mapping and user triggered DMA mapping/unmapping.
> Refer vfio_dma_do_unmap() in drivers/vfio/vfio_iommu_type1.c
> Snippet of comment is below.
>          /*
>           * vfio-iommu-type1 (v1) - User mappings were coalesced together to
>           * avoid tracking individual mappings.  This means that the granularity
>           * of the original mapping was lost and the user was allowed to attempt
>           * to unmap any range.  Depending on the contiguousness of physical
>           * memory and page sizes supported by the IOMMU, arbitrary unmaps may
>           * or may not have worked.  We only guaranteed unmap granularity
>           * matching the original mapping; even though it was untracked here,
>           * the original mappings are reflected in IOMMU mappings.  This
>           * resulted in a couple unusual behaviors.  First, if a range is not
>           * able to be unmapped, ex. a set of 4k pages that was mapped as a
>           * 2M hugepage into the IOMMU, the unmap ioctl returns success but with
>           * a zero sized unmap.  Also, if an unmap request overlaps the first
>           * address of a hugepage, the IOMMU will unmap the entire hugepage.
>           * This also returns success and the returned unmap size reflects the
>           * actual size unmapped.
>           * We attempt to maintain compatibility with this "v1" interface, but
>           * we take control out of the hands of the IOMMU.  Therefore, an unmap
>           * request offset from the beginning of the original mapping will
>           * return success with zero sized unmap.  And an unmap request covering
>           * the first iova of mapping will unmap the entire range.
> This behavior can be verified by using first patch and add return check for
> dma_unmap.size != len in vfio_type1_dma_mem_map()
> v8:
> - Add cc stable to patch 3/3
> v7:
> - Dropped vfio test case of patch 3/4 i.e
>    "test: add test case to validate VFIO DMA map/unmap"
>    as it couldn't be supported in POWER9 system.
> v6:
> - Fixed issue with x86-32 build introduced by v5.
> v5:
> - Changed vfio test in test_vfio.c to use system pages allocated from
>    heap instead of mmap() so that it comes in range of initially configured
>    window for POWER9 System.
> - Added acked-by from David for 1/4, 2/4.
> v4:
> - Fixed issue with patch 4/4 on x86 builds.
> v3:
> - Fixed external memory test case(4/4) to use system page size
>    instead of 4K.
> - Fixed check-git-log.sh issue and rebased.
> - Added acked-by from anatoly.burakov at intel.com to first 3 patches.
> v2:
> - Reverted earlier commit that enables mergin contiguous mapping for
>    IOVA as PA. (see 1/3)
> - Updated documentation about kernel dma mapping limits and vfio
>    module parameter.
> - Moved vfio test to test_vfio.c and handled comments from
>    Anatoly.
> Nithin Dabilpuram (3):
>    vfio: revert changes for map contiguous areas in one go
>    vfio: fix DMA mapping granularity for type1 IOVA as VA
>    test: change external memory test to use system page sz

Is there anything preventing this from getting merged? Let's try for 
21.05 :)


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