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

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Message-ID:
 <IA0PR12MB755536B17795F5188B9493EEABABA@IA0PR12MB7555.namprd12.prod.outlook.com>
Date: Wed, 17 Dec 2025 17:15:58 +0000
From: Shameer Kolothum <skolothumtho@...dia.com>
To: Cédric Le Goater <clg@...hat.com>, 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>, Kevin Tian
	<kevin.tian@...el.com>, Krishnakant Jaju <kjaju@...dia.com>, Matt Ochs
	<mochs@...dia.com>, "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>, "linux-mm@...ck.org"
	<linux-mm@...ck.org>, "linux-doc@...r.kernel.org"
	<linux-doc@...r.kernel.org>, "linux-media@...r.kernel.org"
	<linux-media@...r.kernel.org>, "dri-devel@...ts.freedesktop.org"
	<dri-devel@...ts.freedesktop.org>, "linaro-mm-sig@...ts.linaro.org"
	<linaro-mm-sig@...ts.linaro.org>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "linux-hardening@...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

Hi Cédric,

> -----Original Message-----
> From: Cédric Le Goater <clg@...hat.com>
> Sent: 17 December 2025 17:02
> 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
> 
> External email: Use caution opening links or attachments
> 
> 
> 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 ?

Yes. We do plan to send that support patch soon.

Thanks,
Shameer