Add a new backend to enable using native driver in a VM guest, via a new
virtgpu context type which (indirectly) makes host kernel interface
available in guest and handles the details of mapping buffers to guest,
etc.
Note that fence-fd's are currently a bit awkward, in that they get
signaled by the guest kernel driver (drm/virtio) once virglrenderer in
the host has processed the execbuf, not when host kernel has signaled
the submit fence. For passing buffers to the host (virtio-wl) the egl
context in virglrenderer is used to create a fence on the host side.
But use of out-fence-fd's in guest could have slightly unexpected
results. For this reason we limit all submitqueues to default priority
(so they cannot be preepmted by host egl context). AFAICT virgl and
venus have a similar problem, which will eventually be solveable once we
have RESOURCE_CREATE_SYNC.
Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14900>
Rob Clark