linux-kernel - Re: [PATCH v9 00/11] vfio/pci: Allow MMIO regions to be exported through dma-buf

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Message-ID:
 <SA1PR12MB71997E0FE7E8CD84586FD7E6B0D4A@SA1PR12MB7199.namprd12.prod.outlook.com>
Date: Thu, 20 Nov 2025 17:23:09 +0000
From: Ankit Agrawal <ankita@...dia.com>
To: 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>, 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>, Kees Cook
	<kees@...nel.org>, "Gustavo A. R. Silva" <gustavoars@...nel.org>, Yishai
 Hadas <yishaih@...dia.com>, Shameer Kolothum <skolothumtho@...dia.com>, Kevin
 Tian <kevin.tian@...el.com>, Alex Williamson <alex@...zbot.org>
CC: 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>, Alex Mastro <amastro@...com>, Nicolin Chen
	<nicolinc@...dia.com>, Vivek Kasireddy <vivek.kasireddy@...el.com>
Subject: Re: [PATCH v9 00/11] vfio/pci: Allow MMIO regions to be exported
 through dma-buf

> This series extends the VFIO PCI subsystem to support exporting MMIO
> regions from PCI device BARs as dma-buf objects, enabling safe sharing of
> non-struct page memory with controlled lifetime management. This allows RDMA
> and other subsystems to import dma-buf FDs and build them into memory regions
> for PCI P2P operations.
>
> The series supports a use case for SPDK where a NVMe device will be
> owned by SPDK through VFIO but interacting with a RDMA device. The RDMA
> device may directly access the NVMe CMB or directly manipulate the NVMe
> device's doorbell using PCI P2P.
>
> However, as a general mechanism, it can support many other scenarios with
> VFIO. This dmabuf approach can be usable by iommufd as well for generic
> and safe P2P mappings.
>
> In addition to the SPDK use-case mentioned above, the capability added
> in this patch series can also be useful when a buffer (located in device
> memory such as VRAM) needs to be shared between any two dGPU devices or
> instances (assuming one of them is bound to VFIO PCI) as long as they
> are P2P DMA compatible.
>
> The implementation provides a revocable attachment mechanism using dma-buf
> move operations. MMIO regions are normally pinned as BARs don't change
> physical addresses, but access is revoked when the VFIO device is closed
> or a PCI reset is issued. This ensures kernel self-defense against
> potentially hostile userspace.
>
> The series includes significant refactoring of the PCI P2PDMA subsystem
> to separate core P2P functionality from memory allocation features,
> making it more modular and suitable for VFIO use cases that don't need
> struct page support.
>
> -----------------------------------------------------------------------
> The series is based originally on
> https://lore.kernel.org/all/20250307052248.405803-1-vivek.kasireddy@intel.com/
> but heavily rewritten to be based on DMA physical API.
> -----------------------------------------------------------------------
> The WIP branch can be found here:
> https://git.kernel.org/pub/scm/linux/kernel/git/leon/linux-rdma.git/log/?h=dmabuf-vfio-v9

Acked-by: Ankit Agrawal <ankita@...dia.com>