linux-kernel - Re: [PATCH] vfio: selftests: Add vfio_dma_mapping_mmio

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Message-ID: <aWAhuSgEQzr_hzv9@google.com>
Date: Thu, 8 Jan 2026 21:29:29 +0000
From: David Matlack <dmatlack@...gle.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Alex Williamson <alex@...zbot.org>, Alex Mastro <amastro@...com>,
	Shuah Khan <shuah@...nel.org>, Peter Xu <peterx@...hat.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH] vfio: selftests: Add vfio_dma_mapping_mmio_test

On 2026-01-08 02:33 PM, Jason Gunthorpe wrote:
> On Thu, Jan 08, 2026 at 10:24:19AM -0800, David Matlack wrote:
> > > > Oh, I was thinking about a compatability only flow only in the type 1
> > > > emulation that internally magically converts a VMA to a dmabuf, but I
> > > > haven't written anything.. It is a bit tricky and the type 1 emulation
> > > > has not been as popular as I expected??
> > >
> > > In part because of this gap, I'd guess.  Thanks,
> > 
> > Lack of huge mappings in the IOMMU when using VFIO_TYPE1_IOMMU is
> > another gap I'm aware of.
> > vfio_dma_mapping_test.vfio_type1_iommu_anonymous_hugetlb_1gb.dma_map_unmap
> > fails when IOMMUFD_VFIO_CONTAINER is enabled.
> 
> What is this? I'm not aware of it..

It's one of the test cases within
tools/testing/selftests/vfio/vfio_dma_mapping_test.c.

Here's the output when running with CONFIG_IOMMUFD_VFIO_CONTAINER=y:

  #  RUN           vfio_dma_mapping_test.vfio_type1_iommu_anonymous_hugetlb_1gb.dma_map_unmap ...
  Mapped HVA 0x7f0480000000 (size 0x40000000) at IOVA 0x0
  Searching for IOVA 0x0 in /sys/kernel/debug/iommu/intel/0000:6a:01.0/domain_translation_struct
  Found IOMMU mappings for IOVA 0x0:
  PGD: 0x0000000203475027
  P4D: 0x0000000203476027
  PUD: 0x0000000203477027
  PMD: 0x00000001e7562027
  PTE: 0x00000041c0000067
  # tools/testing/selftests/vfio/vfio_dma_mapping_test.c:188:dma_map_unmap:Expected 0 (0) == mapping.pte (282394099815)
  # dma_map_unmap: Test terminated by assertion
  #          FAIL  vfio_dma_mapping_test.vfio_type1_iommu_anonymous_hugetlb_1gb.dma_map_unmap