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Thu, 20 Nov 2025 19:04:15 -0500 (EST) Date: Thu, 20 Nov 2025 17:04:13 -0700 From: Alex Williamson To: Leon Romanovsky Cc: Bjorn Helgaas , Logan Gunthorpe , Jens Axboe , Robin Murphy , Joerg Roedel , Will Deacon , Marek Szyprowski , Jason Gunthorpe , Andrew Morton , Jonathan Corbet , Sumit Semwal , Christian =?UTF-8?B?S8O2bmln?= , Kees Cook , "Gustavo A. R. Silva" , Ankit Agrawal , Yishai Hadas , Shameer Kolothum , Kevin Tian , Krishnakant Jaju , Matt Ochs , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, iommu@lists.linux.dev, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, kvm@vger.kernel.org, linux-hardening@vger.kernel.org, Vivek Kasireddy Subject: Re: [PATCH v9 10/11] vfio/pci: Add dma-buf export support for MMIO regions Message-ID: <20251120170413.050ccbb5.alex@shazbot.org> In-Reply-To: <20251120-dmabuf-vfio-v9-10-d7f71607f371@nvidia.com> References: <20251120-dmabuf-vfio-v9-0-d7f71607f371@nvidia.com> <20251120-dmabuf-vfio-v9-10-d7f71607f371@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 2A2C740014 X-Stat-Signature: 6xk3ehpz3t3m61gj6yptcxnba4w8wa6g X-Rspam-User: X-HE-Tag: 1763683460-831774 X-HE-Meta: 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 r1KYBLd2 /5G6fsUfbbXiyCpq2BXVaoGhA352dy4kwQdeZi1/NniOgixf+E6x5DohXlOKASxVvsQzIvincsQZQ+pk9amnX+FcYwweZnvqbiPSgw5xaQESNyHDKtLq4NglHBVpdDLn7Z9qW0KjtI7pKEGdrF3vS8HoAT4UgvTfFtXp/aIq1sEsLZDIF+r8ZTCVIRlsCUcvCrFD5bDDuLKH3ggDc+IimhFNCZw46CpA96KyqiUF96MOglZZyald2dGQXbNcPqxSogKWoyclpCK5z9/8Ln6MiUmGFCNvgrDr8eLlH0hzRkVzuD9I4804djCFxYLBPSZHToZzjHOefl8wlIJWz+S+dEo9G1VqdIHhfEtMnJa5QlaZehuwiZfZyU6kHa15oqXTqTvUK X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 20 Nov 2025 11:28:29 +0200 Leon Romanovsky wrote: > diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c > index 142b84b3f225..51a3bcc26f8b 100644 > --- a/drivers/vfio/pci/vfio_pci_core.c > +++ b/drivers/vfio/pci/vfio_pci_core.c ... > @@ -2487,8 +2500,11 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set, > > err_undo: > list_for_each_entry_from_reverse(vdev, &dev_set->device_list, > - vdev.dev_set_list) > + vdev.dev_set_list) { > + if (__vfio_pci_memory_enabled(vdev)) > + vfio_pci_dma_buf_move(vdev, false); > up_write(&vdev->memory_lock); > + } I ran into a bug here. In the hot reset path we can have dev_sets where one or more devices are not opened by the user. The vconfig buffer for the device is established on open. However: bool __vfio_pci_memory_enabled(struct vfio_pci_core_device *vdev) { struct pci_dev *pdev = vdev->pdev; u16 cmd = le16_to_cpu(*(__le16 *)&vdev->vconfig[PCI_COMMAND]); ... Leads to a NULL pointer dereference. I think the most straightforward fix is simply to test the open_count on the vfio_device, which is also protected by the dev_set->lock that we already hold here: --- a/drivers/vfio/pci/vfio_pci_core.c +++ b/drivers/vfio/pci/vfio_pci_core.c @@ -2501,7 +2501,7 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set, err_undo: list_for_each_entry_from_reverse(vdev, &dev_set->device_list, vdev.dev_set_list) { - if (__vfio_pci_memory_enabled(vdev)) + if (vdev->vdev.open_count && __vfio_pci_memory_enabled(vdev)) vfio_pci_dma_buf_move(vdev, false); up_write(&vdev->memory_lock); } Any other suggestions? This should be the only reset path with this nuance of affecting non-opened devices. Thanks, Alex