On Mon, Oct 20, 2025 at 4:42 PM Dmitry Osipenko
<[email protected]> wrote:
>
> Support asynchronous fencing feature of virglrenderer. It allows Qemu to
> handle fence as soon as it's signalled instead of periodically polling
> the fence status. This feature is required for enabling DRM context
> support in Qemu because legacy fencing mode isn't supported for DRM
> contexts in virglrenderer.
>
> Reviewed-by: Akihiko Odaki <[email protected]>
> Acked-by: Michael S. Tsirkin <[email protected]>
> Tested-by: Alex Bennée <[email protected]>
> Reviewed-by: Alex Bennée <[email protected]>
> Signed-off-by: Dmitry Osipenko <[email protected]>
> ---
> hw/display/virtio-gpu-gl.c | 5 ++
> hw/display/virtio-gpu-virgl.c | 130 +++++++++++++++++++++++++++++++++
> include/hw/virtio/virtio-gpu.h | 11 +++
> meson.build | 2 +
> 4 files changed, 148 insertions(+)
>
> diff --git a/hw/display/virtio-gpu-gl.c b/hw/display/virtio-gpu-gl.c
> index c06a078fb36a..1468c6ed1467 100644
> --- a/hw/display/virtio-gpu-gl.c
> +++ b/hw/display/virtio-gpu-gl.c
> @@ -169,6 +169,11 @@ static void virtio_gpu_gl_device_unrealize(DeviceState
> *qdev)
> if (gl->renderer_state >= RS_INITED) {
> #if VIRGL_VERSION_MAJOR >= 1
> qemu_bh_delete(gl->cmdq_resume_bh);
> +
> + if (gl->async_fence_bh) {
> + virtio_gpu_virgl_reset_async_fences(g);
> + qemu_bh_delete(gl->async_fence_bh);
> + }
> #endif
> if (virtio_gpu_stats_enabled(g->parent_obj.conf)) {
> timer_free(gl->print_stats);
> diff --git a/hw/display/virtio-gpu-virgl.c b/hw/display/virtio-gpu-virgl.c
> index cd8b367f6fa6..0320d6deca76 100644
> --- a/hw/display/virtio-gpu-virgl.c
> +++ b/hw/display/virtio-gpu-virgl.c
> @@ -24,6 +24,23 @@
>
> #include <virglrenderer.h>
>
> +/*
> + * VIRGL_CHECK_VERSION available since libvirglrenderer 1.0.1 and was fixed
> + * in 1.1.0. Undefine bugged version of the macro and provide our own.
> + */
> +#if defined(VIRGL_CHECK_VERSION) && \
> + VIRGL_VERSION_MAJOR == 1 && VIRGL_VERSION_MINOR < 1
> +#undef VIRGL_CHECK_VERSION
> +#endif
> +
> +#ifndef VIRGL_CHECK_VERSION
> +#define VIRGL_CHECK_VERSION(major, minor, micro) \
> + (VIRGL_VERSION_MAJOR > (major) || \
> + VIRGL_VERSION_MAJOR == (major) && VIRGL_VERSION_MINOR > (minor) || \
> + VIRGL_VERSION_MAJOR == (major) && VIRGL_VERSION_MINOR == (minor) && \
> + VIRGL_VERSION_MICRO >= (micro))
> +#endif
> +
> struct virtio_gpu_virgl_resource {
> struct virtio_gpu_simple_resource base;
> MemoryRegion *mr;
> @@ -1051,6 +1068,106 @@ static void virgl_write_context_fence(void *opaque,
> uint32_t ctx_id,
> }
> #endif
>
> +void virtio_gpu_virgl_reset_async_fences(VirtIOGPU *g)
> +{
> + struct virtio_gpu_virgl_context_fence *f;
> + VirtIOGPUGL *gl = VIRTIO_GPU_GL(g);
> +
> + while (!QSLIST_EMPTY(&gl->async_fenceq)) {
> + f = QSLIST_FIRST(&gl->async_fenceq);
> +
> + QSLIST_REMOVE_HEAD(&gl->async_fenceq, next);
> +
> + g_free(f);
> + }
> +}
> +
> +#if VIRGL_CHECK_VERSION(1, 1, 2)
> +static void virtio_gpu_virgl_async_fence_bh(void *opaque)
> +{
> + QSLIST_HEAD(, virtio_gpu_virgl_context_fence) async_fenceq;
> + struct virtio_gpu_ctrl_command *cmd, *tmp;
> + struct virtio_gpu_virgl_context_fence *f;
> + VirtIOGPU *g = opaque;
> + VirtIOGPUGL *gl = VIRTIO_GPU_GL(g);
> +
> + if (gl->renderer_state != RS_INITED) {
> + return;
> + }
> +
> + QSLIST_MOVE_ATOMIC(&async_fenceq, &gl->async_fenceq);
> +
> + while (!QSLIST_EMPTY(&async_fenceq)) {
> + f = QSLIST_FIRST(&async_fenceq);
> +
> + QSLIST_REMOVE_HEAD(&async_fenceq, next);
> +
> + QTAILQ_FOREACH_SAFE(cmd, &g->fenceq, next, tmp) {
> + /*
> + * the guest can end up emitting fences out of order
> + * so we should check all fenced cmds not just the first one.
> + */
> + if (cmd->cmd_hdr.fence_id > f->fence_id) {
> + continue;
> + }
> + if (cmd->cmd_hdr.flags & VIRTIO_GPU_FLAG_INFO_RING_IDX) {
> + if (cmd->cmd_hdr.ring_idx != f->ring_idx) {
> + continue;
> + }
> + if (cmd->cmd_hdr.ctx_id != f->ctx_id) {
> + continue;
> + }
> + } else if (f->ring_idx >= 0) {
> + /* ctx0 GL-query fences don't have ring info */
> + continue;
> + }
> + virtio_gpu_ctrl_response_nodata(g, cmd,
> VIRTIO_GPU_RESP_OK_NODATA);
> + QTAILQ_REMOVE(&g->fenceq, cmd, next);
> + g_free(cmd);
> + }
Conditions above are a little bit confusing. Skipping unsignaled
fences first makes sense to me. Next we can use f->ctx_id == 0 to
distinguish ctx0 fence vs context fence. Then:
- for f->ctx_id == 0, skip any RING_IDX
- for f->ctx_id > 0, only care about RING_IDX along with comparing
ctx_id and ring_idx
So, if we check the RING_IDX flag first like in the existing patch,
the else condition is only meaningful for the ctx0 fence, and
f->ring_idx >= 0 will never be evaluated to true. Can we drop the
"else if" part?
> +
> + trace_virtio_gpu_fence_resp(f->fence_id);
> + g_free(f);
> + g->inflight--;
> + if (virtio_gpu_stats_enabled(g->parent_obj.conf)) {
> + trace_virtio_gpu_dec_inflight_fences(g->inflight);
> + }
> + }
> +}
> +
> +static void
> +virtio_gpu_virgl_push_async_fence(VirtIOGPU *g, uint32_t ctx_id,
> + int64_t ring_idx, uint64_t fence_id)
> +{
> + struct virtio_gpu_virgl_context_fence *f;
> + VirtIOGPUGL *gl = VIRTIO_GPU_GL(g);
> +
> + f = g_new(struct virtio_gpu_virgl_context_fence, 1);
> + f->ctx_id = ctx_id;
> + f->ring_idx = ring_idx;
> + f->fence_id = fence_id;
> +
> + QSLIST_INSERT_HEAD_ATOMIC(&gl->async_fenceq, f, next);
> +
> + qemu_bh_schedule(gl->async_fence_bh);
> +}
> +
> +static void virgl_write_async_fence(void *opaque, uint32_t fence)
> +{
> + VirtIOGPU *g = opaque;
> +
> + virtio_gpu_virgl_push_async_fence(g, 0, -1, fence);
> +}
> +
> +static void virgl_write_async_context_fence(void *opaque, uint32_t ctx_id,
> + uint32_t ring_idx, uint64_t
> fence)
> +{
> + VirtIOGPU *g = opaque;
> +
> + virtio_gpu_virgl_push_async_fence(g, ctx_id, ring_idx, fence);
> +}
> +#endif
> +
> static virgl_renderer_gl_context
> virgl_create_context(void *opaque, int scanout_idx,
> struct virgl_renderer_gl_ctx_param *params)
> @@ -1150,6 +1267,8 @@ void virtio_gpu_virgl_reset_scanout(VirtIOGPU *g)
> void virtio_gpu_virgl_reset(VirtIOGPU *g)
> {
> virgl_renderer_reset();
> +
> + virtio_gpu_virgl_reset_async_fences(g);
> }
>
> int virtio_gpu_virgl_init(VirtIOGPU *g)
> @@ -1162,6 +1281,12 @@ int virtio_gpu_virgl_init(VirtIOGPU *g)
> if (qemu_egl_display) {
> virtio_gpu_3d_cbs.version = 4;
> virtio_gpu_3d_cbs.get_egl_display = virgl_get_egl_display;
> +#if VIRGL_CHECK_VERSION(1, 1, 2)
> + virtio_gpu_3d_cbs.write_fence = virgl_write_async_fence;
> + virtio_gpu_3d_cbs.write_context_fence =
> virgl_write_async_context_fence;
> + flags |= VIRGL_RENDERER_ASYNC_FENCE_CB;
> + flags |= VIRGL_RENDERER_THREAD_SYNC;
> +#endif
> }
> #endif
> #ifdef VIRGL_RENDERER_D3D11_SHARE_TEXTURE
> @@ -1195,6 +1320,11 @@ int virtio_gpu_virgl_init(VirtIOGPU *g)
> gl->cmdq_resume_bh = aio_bh_new(qemu_get_aio_context(),
> virtio_gpu_virgl_resume_cmdq_bh,
> g);
> +#if VIRGL_CHECK_VERSION(1, 1, 2)
> + gl->async_fence_bh = aio_bh_new(qemu_get_aio_context(),
> + virtio_gpu_virgl_async_fence_bh,
> + g);
> +#endif
> #endif
>
> return 0;
> diff --git a/include/hw/virtio/virtio-gpu.h b/include/hw/virtio/virtio-gpu.h
> index 9f16f89a36d2..e15c16aa5945 100644
> --- a/include/hw/virtio/virtio-gpu.h
> +++ b/include/hw/virtio/virtio-gpu.h
> @@ -233,6 +233,13 @@ struct VirtIOGPUClass {
> Error **errp);
> };
>
> +struct virtio_gpu_virgl_context_fence {
> + uint32_t ctx_id;
> + int64_t ring_idx;
If I didn't miss anything above, we don't need -1 to tell anything.
Then the ring_idx here can be a uint32_t, and virgl_write_async_fence
can just pass 0.
> + uint64_t fence_id;
> + QSLIST_ENTRY(virtio_gpu_virgl_context_fence) next;
> +};
> +
> /* VirtIOGPUGL renderer states */
> typedef enum {
> RS_START, /* starting state */
> @@ -250,6 +257,9 @@ struct VirtIOGPUGL {
> QEMUTimer *print_stats;
>
> QEMUBH *cmdq_resume_bh;
> +
> + QEMUBH *async_fence_bh;
> + QSLIST_HEAD(, virtio_gpu_virgl_context_fence) async_fenceq;
> };
>
> struct VhostUserGPU {
> @@ -379,5 +389,6 @@ void virtio_gpu_virgl_reset_scanout(VirtIOGPU *g);
> void virtio_gpu_virgl_reset(VirtIOGPU *g);
> int virtio_gpu_virgl_init(VirtIOGPU *g);
> GArray *virtio_gpu_virgl_get_capsets(VirtIOGPU *g);
> +void virtio_gpu_virgl_reset_async_fences(VirtIOGPU *g);
>
> #endif
> diff --git a/meson.build b/meson.build
> index e96c28da09b6..e3d48150483e 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -2597,6 +2597,8 @@ config_host_data.set('CONFIG_VNC_JPEG', jpeg.found())
> config_host_data.set('CONFIG_VNC_SASL', sasl.found())
> if virgl.found()
> config_host_data.set('VIRGL_VERSION_MAJOR', virgl.version().split('.')[0])
> + config_host_data.set('VIRGL_VERSION_MINOR', virgl.version().split('.')[1])
> + config_host_data.set('VIRGL_VERSION_MICRO', virgl.version().split('.')[2])
> endif
> config_host_data.set('CONFIG_VIRTFS', have_virtfs)
> config_host_data.set('CONFIG_VTE', vte.found())
> --
> 2.51.0
>
