linux-kernel - Re: [PATCH v3 0/4] vfio: selftests: update DMA mapping tests to use queried IOVA ranges

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Message-ID: <aRT8v4Yj8Lm5KlUk@devgpu015.cco6.facebook.com>
Date: Wed, 12 Nov 2025 13:31:43 -0800
From: Alex Mastro <amastro@...com>
To: Alex Williamson <alex@...zbot.org>
CC: David Matlack <dmatlack@...gle.com>, Shuah Khan <shuah@...nel.org>,
        Jason
 Gunthorpe <jgg@...pe.ca>, <kvm@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 0/4] vfio: selftests: update DMA mapping tests to use
 queried IOVA ranges

On Wed, Nov 12, 2025 at 08:30:05AM -0700, Alex Williamson wrote:
> On Tue, 11 Nov 2025 10:48:23 -0800
> Alex Mastro <amastro@...com> wrote:
> 
> > Not all IOMMUs support the same virtual address width as the processor,
> > for instance older Intel consumer platforms only support 39-bits of
> > IOMMU address space. On such platforms, using the virtual address as the
> > IOVA and mappings at the top of the address space both fail.
> > 
> > VFIO and IOMMUFD have facilities for retrieving valid IOVA ranges,
> > VFIO_IOMMU_TYPE1_INFO_CAP_IOVA_RANGE and IOMMU_IOAS_IOVA_RANGES,
> > respectively. These provide compatible arrays of ranges from which we
> > can construct a simple allocator.
> > 
> > Use this new allocator in place of reusing the virtual address, and
> > incorporate the maximum supported IOVA into the limit testing.  This
> > latter change doesn't test quite the same absolute end-of-address space
> > behavior but still seems to have some value.
> > 
> > This series is based on Alex Williamson's "Incorporate IOVA range info"
> > [1] along with feedback from the discussion in David Matlack's "Skip
> > vfio_dma_map_limit_test if mapping returns -EINVAL" [2].
> > 
> > Given David's plans to split IOMMU concerns from devices as described
> > in [3], this series' home for `struct iova_allocator` and IOVA
> > range helpers are likely to be short lived, since they reside in
> > vfio_pci_device.c. I assume that the rework can move this functionality
> > to a more appropriate location next to other IOMMU-focused code, once
> > such a place exists.
> > 
> > [1] https://lore.kernel.org/all/20251108212954.26477-1-alex@shazbot.org/#t
> > [2] https://lore.kernel.org/all/20251107222058.2009244-1-dmatlack@google.com/
> > [3] https://lore.kernel.org/all/aRIoKJk0uwLD-yGr@google.com/
> > 
> > To: Alex Williamson <alex@...zbot.org>
> > To: David Matlack <dmatlack@...gle.com>
> > To: Shuah Khan <shuah@...nel.org>
> > To: Jason Gunthorpe <jgg@...pe.ca>
> > Cc: kvm@...r.kernel.org
> > Cc: linux-kselftest@...r.kernel.org
> > Cc: linux-kernel@...r.kernel.org
> > Signed-off-by: Alex Mastro <amastro@...com>
> > 
> > Changes in v3:
> > - Update capability chain cycle detection
> > - Clarify the iova=vaddr commit message
> > - Link to v2: https://lore.kernel.org/r/20251111-iova-ranges-v2-0-0fa267ff9b78@fb.com
> 
> Applied to vfio for-linus branch for v6.18.  Thanks for the quick
> resolution on this!

No problem, thanks for the reviews!

> 
> Alex