Hi Dmitry, > Subject: [PATCH v2 0/5] drm/virtio: Import scanout buffers from other > devices > > Having virtio-gpu import scanout buffers (via prime) from other > devices means that we'd be adding a head to headless GPUs assigned > to a Guest VM or additional heads to regular GPU devices that are > passthrough'd to the Guest. In these cases, the Guest compositor > can render into the scanout buffer using a primary GPU and has the > secondary GPU (virtio-gpu) import it for display purposes. > > The main advantage with this is that the imported scanout buffer can > either be displayed locally on the Host (e.g, using Qemu + GTK UI) > or encoded and streamed to a remote client (e.g, Qemu + Spice UI). > Note that since Qemu uses udmabuf driver, there would be no copies > made of the scanout buffer as it is displayed. This should be > possible even when it might reside in device memory such has VRAM. > > The specific use-case that can be supported with this series is when > running Weston or other guest compositors with "additional-devices" > feature (./weston --drm-device=card1 --additional-devices=card0). > More info about this feature can be found at: > https://gitlab.freedesktop.org/wayland/weston/-/merge_requests/736 > > In the above scenario, card1 could be a dGPU or an iGPU and card0 > would be virtio-gpu in KMS only mode. However, the case where this > patch series could be particularly useful is when card1 is a GPU VF > that needs to share its scanout buffer (in a zero-copy way) with the > GPU PF on the Host. Or, it can also be useful when the scanout buffer > needs to be shared between any two GPU devices (assuming one of them > is assigned to a Guest VM) as long as they are P2P DMA compatible. > > As part of the import, the virtio-gpu driver shares the dma > addresses and lengths with Qemu which then determines whether the > memory region they belong to is owned by a VFIO device or whether it > is part of the Guest's system ram. If it is the former, it uses the > VFIO_DEVICE_FEATURE_DMA_BUF feature flag while invoking the ioctl > against the VFIO device fd and gets a dmabuf fd in return. In the > latter case, Qemu obtains the dmabuf fd using the udmabuf driver. > > Note that the virtio-gpu driver registers a move_notify() callback > to track location changes associated with the scanout buffer and > sends attach/detach backing cmds to Qemu when appropriate. And, > synchronization (that is, ensuring that Guest and Host are not > using the scanout buffer at the same time) is ensured by pinning/ > unpinning the dmabuf as part of prepare/cleanup fb and using a > fence in resource_flush cmd. > > Changelog: > > v1 -> v2: > - Use a fenced version of VIRTIO_GPU_CMD_RESOURCE_DETACH_BACKING > cmd > (Dmitry) Do you have any further comments or suggestions on this series? Thanks, Vivek > > RFC -> v1: > - Use virtio_gpu_cleanup_object() to cleanup the imported obj > - Do pin/unpin as part of prepare and cleanup fb for the imported > dmabuf obj instead doing it as part of plane update > - Tested with gnome-shell/mutter (wayland backend) > > This series is available at: > https://gitlab.freedesktop.org/Vivek/drm-tip/-/commits/virtgpu_import_v2 > > along with additional patches for Qemu and Spice here: > https://gitlab.freedesktop.org/Vivek/qemu/-/commits/vfio_dmabuf_2 > https://gitlab.freedesktop.org/Vivek/spice/-/commits/encode_dmabuf_v8 > > Patchset overview: > > Patch 1: Implement VIRTIO_GPU_CMD_RESOURCE_DETACH_BACKING cmd > Patch 2-3: Helpers to initalize, import, free imported object > Patch 4-5: Import and use buffers from other devices for scanout > > This series is tested using the following method: > - Run Qemu with the following relevant options: > qemu-system-x86_64 -m 4096m .... > -device vfio-pci,host=0000:03:00.0 > -device virtio-vga,max_outputs=1,blob=true,xres=1920,yres=1080 > -spice port=3001,gl=on,disable-ticketing=on,preferred- > codec=gstreamer:h264 > -object memory-backend-memfd,id=mem1,size=4096M > -machine memory-backend=mem1 ... > - Run upstream Weston with the following options in the Guest VM: > ./weston --drm-device=card1 --additional-devices=card0 > - Run gnome-shell/Mutter (wayland backend) with this additional patch: > https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3745 > > where card1 is a DG2 dGPU (passthrough'd and using xe driver in Guest VM), > card0 is virtio-gpu and the Host is using a RPL iGPU. > > Cc: Gerd Hoffmann <kraxel@xxxxxxxxxx> > Cc: Dongwon Kim <dongwon.kim@xxxxxxxxx> > Cc: Daniel Vetter <daniel.vetter@xxxxxxxx> > Cc: Christian Koenig <christian.koenig@xxxxxxx> > Cc: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> > Cc: Rob Clark <robdclark@xxxxxxxxx> > Cc: Gurchetan Singh <gurchetansingh@xxxxxxxxxxxx> > Cc: Chia-I Wu <olvaffe@xxxxxxxxx> > Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx> > Cc: Michal Wajdeczko <michal.wajdeczko@xxxxxxxxx> > Cc: Michael Tretter <m.tretter@xxxxxxxxxxxxxx> > > Vivek Kasireddy (5): > drm/virtio: Implement VIRTIO_GPU_CMD_RESOURCE_DETACH_BACKING > cmd > drm/virtio: Add a helper to map and note the dma addrs and lengths > drm/virtio: Add helpers to initialize and free the imported object > drm/virtio: Import prime buffers from other devices as guest blobs > drm/virtio: Add prepare and cleanup routines for imported dmabuf obj > > drivers/gpu/drm/virtio/virtgpu_drv.h | 10 ++ > drivers/gpu/drm/virtio/virtgpu_object.c | 26 ++++ > drivers/gpu/drm/virtio/virtgpu_plane.c | 71 +++++++++- > drivers/gpu/drm/virtio/virtgpu_prime.c | 170 +++++++++++++++++++++++- > drivers/gpu/drm/virtio/virtgpu_vq.c | 25 ++++ > 5 files changed, 300 insertions(+), 2 deletions(-) > > -- > 2.45.1
