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

David Marchand david.marchand at redhat.com
Mon Mar 1 13:13:32 CET 2021


On Fri, Jan 15, 2021 at 8:33 AM Nithin Dabilpuram
<ndabilpuram at marvell.com> 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()

Series applied, thanks.


-- 
David Marchand



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