drm/virtio: Fix handling CONFIG_DRM_VIRTIO_GPU_KMS option

VirtIO-GPU got a new config option for disabling KMS. There were two
problems left unnoticed during review when the new option was added:

1. The IS_ENABLED(CONFIG_DRM_VIRTIO_GPU_KMS) check in the code was
inverted, hence KMS was disabled when it should be enabled and vice versa.

2. The disabled KMS crashed kernel with a NULL dereference in
drm_kms_helper_hotplug_event(), which shall not be invoked with a
disabled KMS.

Fix the inverted config option check in the code and skip handling the
VIRTIO_GPU_EVENT_DISPLAY sent by host when KMS is disabled in guest to fix
the crash.

Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Fixes: 72122c69d717 ("drm/virtio: Add option to disable KMS support")
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230306163916.1595961-1-dmitry.osipenko@collabora.com

diff --git a/drivers/gpu/drm/virtio/virtgpu_kms.c b/drivers/gpu/drm/virtio/virtgpu_kms.c
index 02e5c18c2c75085e163cf10d246554b319a6e3f6..5a3b5aaed1f36101f4d7c49c441f96539c0f7c8e 100644 (file)
--- a/drivers/gpu/drm/virtio/virtgpu_kms.c
+++ b/drivers/gpu/drm/virtio/virtgpu_kms.c
@@ -43,11 +43,13 @@ static void virtio_gpu_config_changed_work_func(struct work_struct *work)
        virtio_cread_le(vgdev->vdev, struct virtio_gpu_config,
                        events_read, &events_read);
        if (events_read & VIRTIO_GPU_EVENT_DISPLAY) {
-               if (vgdev->has_edid)
-                       virtio_gpu_cmd_get_edids(vgdev);
-               virtio_gpu_cmd_get_display_info(vgdev);
-               virtio_gpu_notify(vgdev);
-               drm_helper_hpd_irq_event(vgdev->ddev);
+               if (vgdev->num_scanouts) {
+                       if (vgdev->has_edid)
+                               virtio_gpu_cmd_get_edids(vgdev);
+                       virtio_gpu_cmd_get_display_info(vgdev);
+                       virtio_gpu_notify(vgdev);
+                       drm_helper_hpd_irq_event(vgdev->ddev);
+               }
                events_clear |= VIRTIO_GPU_EVENT_DISPLAY;
        }
        virtio_cwrite_le(vgdev->vdev, struct virtio_gpu_config,
@@ -224,7 +226,7 @@ int virtio_gpu_init(struct virtio_device *vdev, struct drm_device *dev)
        vgdev->num_scanouts = min_t(uint32_t, num_scanouts,
                                    VIRTIO_GPU_MAX_SCANOUTS);
 
-       if (IS_ENABLED(CONFIG_DRM_VIRTIO_GPU_KMS) || !vgdev->num_scanouts) {
+       if (!IS_ENABLED(CONFIG_DRM_VIRTIO_GPU_KMS) || !vgdev->num_scanouts) {
                DRM_INFO("KMS disabled\n");
                vgdev->num_scanouts = 0;
                vgdev->has_edid = false;
@@ -247,9 +249,9 @@ int virtio_gpu_init(struct virtio_device *vdev, struct drm_device *dev)
 
        if (num_capsets)
                virtio_gpu_get_capsets(vgdev, num_capsets);
-       if (vgdev->has_edid)
-               virtio_gpu_cmd_get_edids(vgdev);
        if (vgdev->num_scanouts) {
+               if (vgdev->has_edid)
+                       virtio_gpu_cmd_get_edids(vgdev);
                virtio_gpu_cmd_get_display_info(vgdev);
                virtio_gpu_notify(vgdev);
                wait_event_timeout(vgdev->resp_wq, !vgdev->display_info_pending,