On 2026-01-08 08:36 PM, Jason Gunthorpe wrote:
> On Thu, Jan 08, 2026 at 09:29:29PM +0000, David Matlack wrote:
> > 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
>
> I can't think of any reason this would fail, I think your tests have
> found a real bug?? Can you check into it, what kernel call fails and
> where does the kernel code come from?
Oh I thought it was by design. This code in iommufd_vfio_set_iommu():
/*
* The difference between TYPE1 and TYPE1v2 is the ability to unmap in
* the middle of mapped ranges. This is complicated by huge page support
* which creates single large IOPTEs that cannot be split by the iommu
* driver. TYPE1 is very old at this point and likely nothing uses it,
* however it is simple enough to emulate by simply disabling the
* problematic large IOPTEs. Then we can safely unmap within any range.
*/
if (type == VFIO_TYPE1_IOMMU)
rc = iopt_disable_large_pages(&ioas->iopt);
git-blame says some guy named Jason Gunthorpe wrote it :P
>
> I don't think I can run these tests with the HW I have??
FWIW all you need any PCI device that can be bound to vfio-pci and
mapped by VT-d. This test does not rely on any of the VFIO selftests
drivers to trigger DMA.
