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[34.124.168.21]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-13e72643a12sm39399784c88.5.2026.07.30.16.33.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Jul 2026 16:33:17 -0700 (PDT) Date: Thu, 30 Jul 2026 23:33:10 +0000 From: Pranjal Shrivastava To: Matt Evans Cc: Alex Williamson , Leon Romanovsky , Jason Gunthorpe , Alex Mastro , Christian =?iso-8859-1?Q?K=F6nig?= , Bjorn Helgaas , Logan Gunthorpe , Kevin Tian , Longfang Liu , Mahmoud Adam , David Matlack , =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= , Sumit Semwal , Ankit Agrawal , Alistair Popple , Vivek Kasireddy , linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, kvm@vger.kernel.org, linux-pci@vger.kernel.org Subject: Re: [PATCH v5 8/9] vfio/pci: Support mmap() of a VFIO DMABUF Message-ID: References: <20260715174737.15287-1-matt@ozlabs.org> <20260715174737.15287-9-matt@ozlabs.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260715174737.15287-9-matt@ozlabs.org> On Wed, Jul 15, 2026 at 06:47:31PM +0100, Matt Evans wrote: > A VFIO DMABUF can export a subset of a BAR to userspace by fd; add > support for mmap() of this fd. This provides another route for a > process to map BARs, in which the process can only map a specific > subset of a BAR represented by the exported DMABUF. > > mmap() support enables userspace driver designs that safely delegate > access to BAR sub-ranges to other client processes by sharing a DMABUF > fd, without having to share the (omnipotent) VFIO device fd with them. > > Since the main VFIO BAR mmap() is now DMABUF-aware, the new mmap() reuses > the existing vm_ops. > > The lifecycle of an exported DMABUF remains decoupled from that of the > device fd it came from, i.e. the device fd could be closed with DMABUF > VMAs present, meaning a fault on a VMA could happen concurrently with > vfio_pci_dma_buf_cleanup(). > > To deal with this scenario, the fault handler now temporarily takes a > VFIO device registration to ensure the vdev remains valid, and then > vdev->memory_lock can be taken on it. > > Signed-off-by: Matt Evans Nice note on locking, enjoyed the lock dance! Reviewed-by: Pranjal Shrivastava Thanks, Praan