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

Nithin Dabilpuram nithind1988 at gmail.com
Mon Feb 22 10:41:46 CET 2021


Ping. 
Can this be merged for 21.05 ? It is pending since few releases.

--
Thanks
Nihtin

On Tue, Feb 16, 2021 at 01:14:37PM +0000, Burakov, Anatoly wrote:
> 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
> :)
> 
> -- 
> Thanks,
> Anatoly


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