hw/display: fix virgl reset regression

Before commit 49afbca3 ("virtio-gpu: drop
use_virgl_renderer"), use_virgl_renderer was preventing calling GL
functions from non-GL context threads. The innocuously looking

  g->parent_obj.use_virgl_renderer = false;

was set the first time virtio_gpu_gl_reset() was called, during
pc_machine_reset() in the main thread. Further virtio_gpu_gl_reset()
calls in IO threads, without associated GL context, were thus skipping
GL calls and avoided warnings or crashes (see also
https://gitlab.freedesktop.org/virgl/virglrenderer/-/issues/226

).

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20210702123221.942432-1-marcandre.lureau@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw/display/virtio-gpu-gl.c

@@ -51,12 +51,7 @@ static void virtio_gpu_gl_update_cursor_data(VirtIOGPU *g,
 static void virtio_gpu_gl_flushed(VirtIOGPUBase *b)
 {
     VirtIOGPU *g = VIRTIO_GPU(b);
-    VirtIOGPUGL *gl = VIRTIO_GPU_GL(b);
 
-    if (gl->renderer_reset) {
-        gl->renderer_reset = false;
-        virtio_gpu_virgl_reset(g);
-    }
     virtio_gpu_process_cmdq(g);
 }
 
@@ -74,6 +69,10 @@ static void virtio_gpu_gl_handle_ctrl(VirtIODevice *vdev, VirtQueue *vq)
         virtio_gpu_virgl_init(g);
         gl->renderer_inited = true;
     }
+    if (gl->renderer_reset) {
+        gl->renderer_reset = false;
+        virtio_gpu_virgl_reset(g);
+    }
 
     cmd = virtqueue_pop(vq, sizeof(struct virtio_gpu_ctrl_command));
     while (cmd) {
@@ -95,12 +94,13 @@ static void virtio_gpu_gl_reset(VirtIODevice *vdev)
 
     virtio_gpu_reset(vdev);
 
-    if (gl->renderer_inited) {
-        if (g->parent_obj.renderer_blocked) {
-            gl->renderer_reset = true;
-        } else {
-            virtio_gpu_virgl_reset(g);
-        }
+    /*
+     * GL functions must be called with the associated GL context in main
+     * thread, and when the renderer is unblocked.
+     */
+    if (gl->renderer_inited && !gl->renderer_reset) {
+        virtio_gpu_virgl_reset_scanout(g);
+        gl->renderer_reset = true;
     }
 }
 

hw/display/virtio-gpu-virgl.c

@@ -588,17 +588,21 @@ void virtio_gpu_virgl_fence_poll(VirtIOGPU *g)
     virtio_gpu_fence_poll(g);
 }
 
-void virtio_gpu_virgl_reset(VirtIOGPU *g)
+void virtio_gpu_virgl_reset_scanout(VirtIOGPU *g)
 {
     int i;
 
-    virgl_renderer_reset();
     for (i = 0; i < g->parent_obj.conf.max_outputs; i++) {
         dpy_gfx_replace_surface(g->parent_obj.scanout[i].con, NULL);
         dpy_gl_scanout_disable(g->parent_obj.scanout[i].con);
     }
 }
 
+void virtio_gpu_virgl_reset(VirtIOGPU *g)
+{
+    virgl_renderer_reset();
+}
+
 int virtio_gpu_virgl_init(VirtIOGPU *g)
 {
     int ret;

include/hw/virtio/virtio-gpu.h

@@ -279,6 +279,7 @@ int virtio_gpu_update_dmabuf(VirtIOGPU *g,
 void virtio_gpu_virgl_process_cmd(VirtIOGPU *g,
                                   struct virtio_gpu_ctrl_command *cmd);
 void virtio_gpu_virgl_fence_poll(VirtIOGPU *g);
+void virtio_gpu_virgl_reset_scanout(VirtIOGPU *g);
 void virtio_gpu_virgl_reset(VirtIOGPU *g);
 int virtio_gpu_virgl_init(VirtIOGPU *g);
 int virtio_gpu_virgl_get_num_capsets(VirtIOGPU *g);