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vhost-device-gpu: Add blob resource support and Venus capset for virglrenderer backend - #988

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dorindabassey:blob-resources-v3
Sep 24, 2026
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vhost-device-gpu: Add blob resource support and Venus capset for virglrenderer backend#988
aesteve-rh merged 8 commits into
rust-vmm:mainfrom
dorindabassey:blob-resources-v3

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@dorindabassey

@dorindabassey dorindabassey commented Aug 3, 2026 •
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Summary of the PR

Implement blob resource creation, mapping, and unmapping for the
virglrenderer backend, using SHMEM_MAP/UNMAP via vhost-user-backend.

This also adds per-context fence support needed for Venus multi-timeline
signaling, dynamic capset index lookup, and Venus capset exposure.

Tested with vkcube in a QEMU guest. Testing with QEMU requires the
vhost-user-gpu SHMEM support patch:
https://lore.kernel.org/all/20260717134920.265128-4-dbassey@redhat.com/

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@dorindabassey dorindabassey changed the title gpu: Add blob resource support vhost-device-gpu: Add blob resource support Aug 4, 2026
@dorindabassey dorindabassey changed the title vhost-device-gpu: Add blob resource support vhost-device-gpu: Add blob resource support and Venus capset for virglrenderer backend Aug 4, 2026
@dorindabassey
dorindabassey force-pushed the blob-resources-v3 branch 2 times, most recently from c5cc017 to 015a08c Compare August 4, 2026 09:35
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dorindabassey commented Aug 4, 2026

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CI failing, passing depends on - rust-vmm/rust-vmm-container#149

@mtjhrc mtjhrc mentioned this pull request Aug 4, 2026
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@dorindabassey
dorindabassey force-pushed the blob-resources-v3 branch 3 times, most recently from 7e7cd16 to da3259f Compare August 10, 2026 10:22
@dorindabassey
dorindabassey force-pushed the blob-resources-v3 branch 4 times, most recently from 15db044 to 9d25314 Compare August 19, 2026 09:32
@dorindabassey
dorindabassey force-pushed the blob-resources-v3 branch 6 times, most recently from 5592003 to 2fe0a59 Compare September 2, 2026 14:52
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dorindabassey commented Sep 2, 2026

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Hi @stefano-garzarella and @epilys, this PR is ready for review now Thanks.

aesteve-rh
aesteve-rh requested changes Sep 18, 2026
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Good work! Some comments here and there. I would reorganize the series a bit: split commit 4 into two commits (SHMEM/protocol vs blob commands), squash 5+7.

Comment thread vhost-device-gpu/src/device.rs
Comment thread vhost-device-gpu/src/device.rs
Comment thread vhost-device-gpu/src/lib.rs
Comment thread vhost-device-gpu/src/device.rs
Comment thread vhost-device-gpu/src/backend/common.rs
Comment thread vhost-device-gpu/src/backend/virgl.rs Outdated
Comment thread vhost-device-gpu/src/backend/virgl.rs
Dorinda Bassey and others added 3 commits September 21, 2026 11:56
Dorinda Bassey
gpu/virgl: Update virglrenderer-rs dependency
406448d 
Update virglrenderer-rs to pull in new API wrappers needed
for Venus support: context_create_fence, context_poll, and
export_resource_dmabuf.

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
@mtjhrc Dorinda Bassey
gpu/virgl: Make capset handling robust
7c51baf 
Instead of hardcoding the capset indices, lookup the capset index dynamically
based on the configured capsets in the config.

Convert the capset bitmask to a capset ID using trailing_zeros() since
bits() returns a power-of-2 bitmask, not the capset index.

Signed-off-by: Matej Hrica <mhrica@redhat.com>
Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
Dorinda Bassey
gpu/virgl: Add per-context fence support
b77e8e7 
Dispatch to context_create_fence() when the guest sets
VIRTIO_GPU_FLAG_INFO_RING_IDX, and poll per-context fences
in event_poll(). This is required for Venus multi-timeline
fence signaling.

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
@dorindabassey
dorindabassey force-pushed the blob-resources-v3 branch 3 times, most recently from c11b250 to 7303896 Compare September 21, 2026 13:34
aesteve-rh
aesteve-rh reviewed Sep 21, 2026
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Comment thread vhost-device-gpu/src/protocol.rs Outdated
aesteve-rh
aesteve-rh reviewed Sep 21, 2026
View reviewed changes
Comment thread vhost-device-gpu/src/device.rs Outdated
aesteve-rh
aesteve-rh reviewed Sep 21, 2026
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Comment thread vhost-device-gpu/README.md
mtjhrc and others added 5 commits September 21, 2026 16:39
@mtjhrc Dorinda Bassey
gpu: Add blob resource support
b113f0f 
Implement blob resource creation, mapping, and unmapping for the
virglrenderer backend. Blob resources enable zero-copy memory sharing
between guest and host, required for Venus (Vulkan) and hardware-
accelerated gfxstream rendering.

This is an atomic feature requiring both vhost-user protocol
infrastructure and virtio-gpu command handlers:

SHMEM/Protocol Infrastructure:
- Advertise SHMEM, BACKEND_REQ, and BACKEND_SEND_FD protocol features
- Implement get_shmem_config() returning 8GB HOST_VISIBLE region size
- Store backend_req_fd for SHMEM_MAP/UNMAP communication with frontend
- Add VIRTIO_GPU_SHM_ID_HOST_VISIBLE field
- Change attach_backing to take Arc<GuestMemoryMmap> to keep guest
memory alive while blob resource iovecs reference it

Blob Command Implementation:
- resource_create_blob: convert HOST3D to HOST3D_GUEST memory type,
create virglrenderer resource with guest-visible iovecs
- resource_map_blob: map blob into SHMEM region, send offset to
frontend via VHOST_USER_BACKEND_SHMEM_MAP
- resource_unmap_blob: unmap from SHMEM, notify frontend via
VHOST_USER_BACKEND_SHMEM_UNMAP
- set_scanout: re-export dmabuf on every scanout (fixes Venus
flickering with cached handles)
- Added UUID field initialization in virglrenderer for blob resources
- Added tests

Code coverage drops by ~0.5% because blob resource integration paths
(resource_create_blob with backing vecs, map/unmap SHMEM communication)
require virglrenderer GPU context not available in CI. However
manual testing in the guest with vkcube confirms functionality.

Signed-off-by: Matej Hrica <mhrica@redhat.com>
Co-authored-by: Dorinda Bassey <dbassey@redhat.com>
@mtjhrc Dorinda Bassey
gpu: Configure virglrenderer based on requested capsets
1494dce 
Expose Venus capability set support using the virglrenderer backend,
enabled by the new blob resource support. Configure virglrenderer
based on the user's capset selection. Enable virgl renderer if VIRGL
or VIRGL2 capsets are requested, and Enable Venus/render-server if
VENUS capset is requested.

Signed-off-by: Matej Hrica <mhrica@redhat.com>
Co-authored-by: Dorinda Bassey <dbassey@redhat.com>
@mtjhrc Dorinda Bassey
gpu: Fix context name parsing for raw strings
27f3b66 
Use String::from_utf8_lossy() instead of
CStr::from_bytes_with_nul() since the virtio-gpu
driver sends debug_name without null terminator.

Signed-off-by: Matej Hrica <mhrica@redhat.com>
Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
Dorinda Bassey
gpu: Add blob_alignment config field
b443495 
Add the blob_alignment field to VirtioGpuConfig to match
the virtio-gpu spec, and set it to the system page size.
This is a new config introduced in the spec and QEMU.

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
Dorinda Bassey
gpu: Add test coverage for SUBMIT_3D command
33a19ae 
Add test case for VIRTIO_GPU_CMD_SUBMIT_3D in test
display_output. This exercises the submit_cmd and
context_create_fence code paths that were previously
untested.

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
aesteve-rh
aesteve-rh approved these changes Sep 21, 2026
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Commit 4 is still a bit long, which makes it harder to review (not saying it needs another split, as we discussed that already!).

Either way, nothing major stood out on this pass. If we catch anything later it can be a follow-up.

Looks good to me, thanks!

@aesteve-rh
aesteve-rh merged commit 057db3e into rust-vmm:main Sep 24, 2026
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@aesteve-rh aesteve-rh aesteve-rh approved these changes
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