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Tsirkin" To: Dmitry Osipenko Cc: Honglei Huang , David Airlie , Gerd Hoffmann , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Simona Vetter , Gurchetan Singh , Chia-I Wu , dri-devel@lists.freedesktop.org, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH] drm/virtio: fix host visible memory detection in virtio-gpu Message-ID: <20250827093320-mutt-send-email-mst@kernel.org> References: <20250827081231.1878248-1-honglei1.huang@amd.com> <9ecf015d-d96a-40ac-a7fb-50e46c4f6e00@collabora.com> 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: <9ecf015d-d96a-40ac-a7fb-50e46c4f6e00@collabora.com> On Wed, Aug 27, 2025 at 03:52:05PM +0300, Dmitry Osipenko wrote: > On 8/27/25 11:12, Honglei Huang wrote: > > From: Honglei Huang > > > > Commit 206cc44588f7 ("virtio: reject shm region if length is zero") > > enhanced the validation in virtio_get_shm_region() by adding a check > > for a zero-length shared memory region. > > > > It is performed before the underlying transport's .get_shm_region() > > implementation is called. This creates an issue in the virtio-gpu > > driver, where the `region` struct is part of a larger structure > > that is zero-initialized by drmm_kzalloc(). > > > > Consequently, the `len` field is 0 at the time of the check, causing > > virtio_get_shm_region() to return false prematurely. This prevents the > > host visible memory feature from being enabled, even when the device > > supports it. > > > > To resolve this, this patch bypasses the inline helper and calls the > > underlying vdev->config->get_shm_region() function pointer directly. > > This ensures that the region's parameters are checked only after they > > have been populated by the transport, aligning with the intended logic. > > > > Signed-off-by: Honglei Huang > > --- > > drivers/gpu/drm/virtio/virtgpu_kms.c | 6 ++++-- > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/gpu/drm/virtio/virtgpu_kms.c b/drivers/gpu/drm/virtio/virtgpu_kms.c > > index 7dfb2006c561..ed5981248302 100644 > > --- a/drivers/gpu/drm/virtio/virtgpu_kms.c > > +++ b/drivers/gpu/drm/virtio/virtgpu_kms.c > > @@ -174,8 +174,10 @@ int virtio_gpu_init(struct virtio_device *vdev, struct drm_device *dev) > > if (virtio_has_feature(vgdev->vdev, VIRTIO_GPU_F_RESOURCE_BLOB)) { > > vgdev->has_resource_blob = true; > > } > > - if (virtio_get_shm_region(vgdev->vdev, &vgdev->host_visible_region, > > - VIRTIO_GPU_SHM_ID_HOST_VISIBLE)) { > > + if (vgdev->vdev->config->get_shm_region && > > + vgdev->vdev->config->get_shm_region( > > + vgdev->vdev, &vgdev->host_visible_region, > > + VIRTIO_GPU_SHM_ID_HOST_VISIBLE)) { > > if (!devm_request_mem_region(&vgdev->vdev->dev, > > vgdev->host_visible_region.addr, > > vgdev->host_visible_region.len, > > Hi, virtio_get_shm_region() change has been reverted by [1]. Don't think > anything else needs to be done. > > [1] > https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?h=next-20250827&id=ced17ee32a9988b8a260628e7c31a100d7dc082e > > +cc Michael Tsirkin > > Might be only good to send a stable kernel PR with that revert. I see > patch available only in linux-next, while stable kernels need to be > fixed sooner. sooner than what?