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Tsirkin" To: Igor Torrente Cc: sami.md.ko@gmail.com, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, eperezma@redhat.com, xuanzhuo@linux.alibaba.com, jasowang@redhat.com, dmitry.osipenko@collabora.com Subject: Re: [PATCH] Revert "virtio: reject shm region if length is zero" Message-ID: <20250807084310-mutt-send-email-mst@kernel.org> References: <20250807124145.81816-1-igor.torrente@collabora.com> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <20250807124145.81816-1-igor.torrente@collabora.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: wDP3rz_t2E22y-qdQr1VkjVeflUZlBFSsl4tAvKORSQ_1754570760 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Thu, Aug 07, 2025 at 09:41:45AM -0300, Igor Torrente wrote: > This reverts commit 206cc44588f72b49ad4d7e21a7472ab2a72a83df. > No that's not enough. Explain the why not the what. for example ------- The commit 206cc44588f7 ("virtio: reject shm region if length is zero") breaks the Virtio-gpu `host_visible` feature. As you can see in the snippet below, host_visible_region is zero because of the `kzalloc`. It's using the `vm_get_shm_region` (drivers/virtio/virtio_mmio.c:536) to read the `addr` and `len` from qemu/crosvm. ``` drivers/gpu/drm/virtio/virtgpu_kms.c 132 vgdev = drmm_kzalloc(dev, sizeof(struct virtio_gpu_device), GFP_KERNEL); [...] 177 if (virtio_get_shm_region(vgdev->vdev, &vgdev->host_visible_region, 178 VIRTIO_GPU_SHM_ID_HOST_VISIBLE)) { ``` Now it always fails. To fix, revert the offending commit. Fixes: 206cc44588f7 ("virtio: reject shm region if length is zero` breaks the Virtio-gpu `host_visible") ------- > Signed-off-by: Igor Torrente > --- > include/linux/virtio_config.h | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h > index b3e1d30c765b..169c7d367fac 100644 > --- a/include/linux/virtio_config.h > +++ b/include/linux/virtio_config.h > @@ -329,8 +329,6 @@ static inline > bool virtio_get_shm_region(struct virtio_device *vdev, > struct virtio_shm_region *region, u8 id) > { > - if (!region->len) > - return false; > if (!vdev->config->get_shm_region) > return false; > return vdev->config->get_shm_region(vdev, region, id); > -- > 2.49.0