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

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Message-ID: <20260108005406.GA545276@ziepe.ca>
Date: Wed, 7 Jan 2026 20:54:06 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: David Matlack <dmatlack@...gle.com>
Cc: Alex Mastro <amastro@...com>, Alex Williamson <alex@...zbot.org>,
	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 Wed, Jan 07, 2026 at 11:54:09PM +0000, David Matlack wrote:
> On 2026-01-07 02:13 PM, Alex Mastro wrote:
> > Test MMIO-backed DMA mappings by iommu_map()-ing mmap'ed BAR regions.
> 
> Thanks for adding this!
> 
> > Also update vfio_pci_bar_map() to align BAR mmaps for efficient huge
> > page mappings.
> > 
> > Only vfio_type1 variants are tested; iommufd variants can be added
> > once kernel support lands.
> 
> Are there plans to support mapping BARs via virtual address in iommufd?
> I thought the plan was only to support via dma-bufs. Maybe Jason can
> confirm.

Only dmabuf.

> Assuming not, should we add negative tests here to make sure iommufd
> does not allow mapping BARs?

Yes
 
> And then we can add dma-buf tests in a future commit.

Yes

Jason