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

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Message-ID: <9d06837d-7aed-43ef-87c2-1ce4f921dff2@redhat.com>
Date: Wed, 17 Dec 2025 18:01:48 +0100
From: Cédric Le Goater <clg@...hat.com>
To: Nicolin Chen <nicolinc@...dia.com>, Leon Romanovsky <leon@...nel.org>
Cc: 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>,
 Jason Gunthorpe <jgg@...pe.ca>, 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

Hello Nicolin,

On 11/4/25 20:19, 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
> 
> Tested-by: Nicolin Chen <nicolinc@...dia.com>

Do you plan to provide P2P support with IOMMUFD for QEMU ?

Thanks,

C.