linux-kernel - Re: [PATCH v6 00/11] vfio/pci: Allow MMIO regions to be exported through dma-buf

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Message-ID: <20251104192616.GJ1204670@ziepe.ca>
Date: Tue, 4 Nov 2025 15:26:16 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: Leon Romanovsky <leon@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Logan Gunthorpe <logang@...tatee.com>, Jens Axboe <axboe@...nel.dk>,
	Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Christian König <christian.koenig@....com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Kees Cook <kees@...nel.org>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Ankit Agrawal <ankita@...dia.com>,
	Yishai Hadas <yishaih@...dia.com>,
	Shameer Kolothum <skolothumtho@...dia.com>,
	Kevin Tian <kevin.tian@...el.com>,
	Krishnakant Jaju <kjaju@...dia.com>, Matt Ochs <mochs@...dia.com>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-block@...r.kernel.org, iommu@...ts.linux.dev,
	linux-mm@...ck.org, linux-doc@...r.kernel.org,
	linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linaro-mm-sig@...ts.linaro.org, kvm@...r.kernel.org,
	linux-hardening@...r.kernel.org,
	Vivek Kasireddy <vivek.kasireddy@...el.com>
Subject: Re: [PATCH v6 00/11] vfio/pci: Allow MMIO regions to be exported
 through dma-buf

On Tue, Nov 04, 2025 at 11:19:43AM -0800, Nicolin Chen wrote:
> On Sun, Nov 02, 2025 at 10:00:48AM +0200, Leon Romanovsky wrote:
> > Changelog:
> > v6:
> >  * Fixed wrong error check from pcim_p2pdma_init().
> >  * Documented pcim_p2pdma_provider() function.
> >  * Improved commit messages.
> >  * Added VFIO DMA-BUF selftest.
> >  * Added __counted_by(nr_ranges) annotation to struct vfio_device_feature_dma_buf.
> >  * Fixed error unwind when dma_buf_fd() fails.
> >  * Document latest changes to p2pmem.
> >  * Removed EXPORT_SYMBOL_GPL from pci_p2pdma_map_type.
> >  * Moved DMA mapping logic to DMA-BUF.
> >  * Removed types patch to avoid dependencies between subsystems.
> >  * Moved vfio_pci_dma_buf_move() in err_undo block.
> >  * Added nvgrace patch.
> 
> I have verified this v6 using Jason's iommufd dmabuf branch:
> https://github.com/jgunthorpe/linux/commits/iommufd_dmabuf/
> 
> by drafting a QEMU patch on top of Shameer's vSMMU v5 series:
> https://github.com/nicolinc/qemu/commits/wip/iommufd_dmabuf/
> 
> with that, I see GPU BAR memory be correctly fetched in the QEMU:
> vfio_region_dmabuf Device 0009:01:00.0, region "0009:01:00.0 BAR 0", offset: 0x0, size: 0x1000000
> vfio_region_dmabuf Device 0009:01:00.0, region "0009:01:00.0 BAR 2", offset: 0x0, size: 0x44f00000
> vfio_region_dmabuf Device 0009:01:00.0, region "0009:01:00.0 BAR 4", offset: 0x0, size: 0x17a0000000

Great thanks! This means we finally have a solution to that follow_pfn
lifetime problem in type 1! What a long journey :)

For those following along this same flow will be used with KVM to
allow it to map VFIO as well. Confidential Compute will require this
because some arches can't put confidential MMIO (or RAM) into a VMA.

Jason