[PATCH] drm/virtio: Add drm_panic support

Ryosuke Yasuoka posted 1 patch 3 weeks, 3 days ago
There is a newer version of this series
drivers/gpu/drm/virtio/virtgpu_drv.h   |  28 +++++
drivers/gpu/drm/virtio/virtgpu_plane.c | 161 +++++++++++++++++++++++++
drivers/gpu/drm/virtio/virtgpu_vq.c    | 156 +++++++++++++++++++++++-
3 files changed, 339 insertions(+), 6 deletions(-)
[PATCH] drm/virtio: Add drm_panic support
Posted by Ryosuke Yasuoka 3 weeks, 3 days ago
From: Jocelyn Falempe <jfalempe@redhat.com>

Virtio gpu supports the drm_panic module, which displays a message to
the screen when a kernel panic occurs.

Signed-off-by: Ryosuke Yasuoka <ryasuoka@redhat.com>
Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
---
 drivers/gpu/drm/virtio/virtgpu_drv.h   |  28 +++++
 drivers/gpu/drm/virtio/virtgpu_plane.c | 161 +++++++++++++++++++++++++
 drivers/gpu/drm/virtio/virtgpu_vq.c    | 156 +++++++++++++++++++++++-
 3 files changed, 339 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h b/drivers/gpu/drm/virtio/virtgpu_drv.h
index 64c236169db8..765698a6dfa3 100644
--- a/drivers/gpu/drm/virtio/virtgpu_drv.h
+++ b/drivers/gpu/drm/virtio/virtgpu_drv.h
@@ -125,7 +125,14 @@ struct virtio_gpu_object_array {
 	struct drm_gem_object *objs[] __counted_by(total);
 };
 
+#define MAX_INLINE_CMD_SIZE   96
+#define MAX_INLINE_RESP_SIZE  24
+#define VBUFFER_SIZE	      (sizeof(struct virtio_gpu_vbuffer) \
+			      + MAX_INLINE_CMD_SIZE		 \
+			      + MAX_INLINE_RESP_SIZE)
+
 struct virtio_gpu_vbuffer;
+struct virtio_gpu_vbuffer_inline;
 struct virtio_gpu_device;
 
 typedef void (*virtio_gpu_resp_cb)(struct virtio_gpu_device *vgdev,
@@ -329,12 +336,26 @@ void virtio_gpu_cmd_create_resource(struct virtio_gpu_device *vgdev,
 				    struct virtio_gpu_fence *fence);
 void virtio_gpu_cmd_unref_resource(struct virtio_gpu_device *vgdev,
 				   struct virtio_gpu_object *bo);
+void virtio_gpu_panic_cmd_transfer_to_host_2d(struct virtio_gpu_device *vgdev,
+					      uint64_t offset,
+					      uint32_t width, uint32_t height,
+					      uint32_t x, uint32_t y,
+					      struct virtio_gpu_object_array *objs,
+					      struct virtio_gpu_fence *fence,
+					      struct virtio_gpu_vbuffer *vbuf);
 void virtio_gpu_cmd_transfer_to_host_2d(struct virtio_gpu_device *vgdev,
 					uint64_t offset,
 					uint32_t width, uint32_t height,
 					uint32_t x, uint32_t y,
 					struct virtio_gpu_object_array *objs,
 					struct virtio_gpu_fence *fence);
+void virtio_gpu_panic_cmd_resource_flush(struct virtio_gpu_device *vgdev,
+					 struct virtio_gpu_vbuffer *vbuf,
+					 uint32_t resource_id,
+					 uint32_t x, uint32_t y,
+					 uint32_t width, uint32_t height,
+					 struct virtio_gpu_object_array *objs,
+					 struct virtio_gpu_fence *fence);
 void virtio_gpu_cmd_resource_flush(struct virtio_gpu_device *vgdev,
 				   uint32_t resource_id,
 				   uint32_t x, uint32_t y,
@@ -399,6 +420,7 @@ void virtio_gpu_ctrl_ack(struct virtqueue *vq);
 void virtio_gpu_cursor_ack(struct virtqueue *vq);
 void virtio_gpu_dequeue_ctrl_func(struct work_struct *work);
 void virtio_gpu_dequeue_cursor_func(struct work_struct *work);
+void virtio_gpu_panic_notify(struct virtio_gpu_device *vgdev);
 void virtio_gpu_notify(struct virtio_gpu_device *vgdev);
 
 int
@@ -435,6 +457,12 @@ struct drm_plane *virtio_gpu_plane_init(struct virtio_gpu_device *vgdev,
 					enum drm_plane_type type,
 					int index);
 
+struct virtio_gpu_vbuffer_inline {
+	struct virtio_gpu_vbuffer base;
+	u8 cmd_buf[MAX_INLINE_CMD_SIZE];
+	u8 resp_buf[MAX_INLINE_RESP_SIZE];
+};
+
 /* virtgpu_fence.c */
 struct virtio_gpu_fence *virtio_gpu_fence_alloc(struct virtio_gpu_device *vgdev,
 						uint64_t base_fence_ctx,
diff --git a/drivers/gpu/drm/virtio/virtgpu_plane.c b/drivers/gpu/drm/virtio/virtgpu_plane.c
index a72a2dbda031..84b65f6b0906 100644
--- a/drivers/gpu/drm/virtio/virtgpu_plane.c
+++ b/drivers/gpu/drm/virtio/virtgpu_plane.c
@@ -26,6 +26,8 @@
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_damage_helper.h>
 #include <drm/drm_fourcc.h>
+#include <drm/drm_managed.h>
+#include <drm/drm_panic.h>
 
 #include "virtgpu_drv.h"
 
@@ -108,6 +110,28 @@ static int virtio_gpu_plane_atomic_check(struct drm_plane *plane,
 	return ret;
 }
 
+/* For drm panic */
+static void virtio_gpu_panic_update_dumb_bo(struct virtio_gpu_device *vgdev,
+					    struct drm_plane_state *state,
+					    struct drm_rect *rect,
+					    struct virtio_gpu_object_array *objs,
+					    struct virtio_gpu_vbuffer *vbuf)
+{
+	struct virtio_gpu_object *bo =
+		gem_to_virtio_gpu_obj(state->fb->obj[0]);
+	uint32_t w = rect->x2 - rect->x1;
+	uint32_t h = rect->y2 - rect->y1;
+	uint32_t x = rect->x1;
+	uint32_t y = rect->y1;
+	uint32_t off = x * state->fb->format->cpp[0] +
+		y * state->fb->pitches[0];
+
+	virtio_gpu_array_add_obj(objs, &bo->base.base);
+
+	virtio_gpu_panic_cmd_transfer_to_host_2d(vgdev, off, w, h, x, y,
+						 objs, NULL, vbuf);
+}
+
 static void virtio_gpu_update_dumb_bo(struct virtio_gpu_device *vgdev,
 				      struct drm_plane_state *state,
 				      struct drm_rect *rect)
@@ -131,6 +155,24 @@ static void virtio_gpu_update_dumb_bo(struct virtio_gpu_device *vgdev,
 					   objs, NULL);
 }
 
+/* For drm_panic */
+static void virtio_gpu_panic_resource_flush(struct drm_plane *plane,
+					    struct virtio_gpu_vbuffer *vbuf,
+					    uint32_t x, uint32_t y,
+					    uint32_t width, uint32_t height)
+{
+	struct drm_device *dev = plane->dev;
+	struct virtio_gpu_device *vgdev = dev->dev_private;
+	struct virtio_gpu_framebuffer *vgfb;
+	struct virtio_gpu_object *bo;
+
+	vgfb = to_virtio_gpu_framebuffer(plane->state->fb);
+	bo = gem_to_virtio_gpu_obj(vgfb->base.obj[0]);
+
+	virtio_gpu_panic_cmd_resource_flush(vgdev, vbuf, bo->hw_res_handle, x, y,
+					    width, height, NULL, NULL);
+}
+
 static void virtio_gpu_resource_flush(struct drm_plane *plane,
 				      uint32_t x, uint32_t y,
 				      uint32_t width, uint32_t height)
@@ -359,11 +401,123 @@ static void virtio_gpu_cursor_plane_update(struct drm_plane *plane,
 	virtio_gpu_cursor_ping(vgdev, output);
 }
 
+static int virtio_drm_get_scanout_buffer(struct drm_plane *plane,
+					 struct drm_scanout_buffer *sb)
+{
+	struct virtio_gpu_object *bo;
+
+	if (!plane->state || !plane->state->fb || !plane->state->visible)
+		return -ENODEV;
+
+	bo = gem_to_virtio_gpu_obj(plane->state->fb->obj[0]);
+
+	/* try to vmap it if possible */
+	if (!bo->base.vaddr) {
+		int ret;
+
+		ret = drm_gem_shmem_vmap(&bo->base, &sb->map[0]);
+		if (ret)
+			return ret;
+	} else {
+		iosys_map_set_vaddr(&sb->map[0], bo->base.vaddr);
+	}
+
+	sb->format = plane->state->fb->format;
+	sb->height = plane->state->fb->height;
+	sb->width = plane->state->fb->width;
+	sb->pitch[0] = plane->state->fb->pitches[0];
+	return 0;
+}
+
+struct virtio_gpu_panic_object_array {
+	struct ww_acquire_ctx ticket;
+	struct list_head next;
+	u32 nents, total;
+	struct drm_gem_object *objs;
+};
+
+static void *virtio_panic_buffer;
+
+static void virtio_gpu_panic_get_vbuf(struct virtqueue *vq,
+				      struct virtio_gpu_vbuffer *vbuf,
+				      struct list_head *reclaim_list)
+{
+	unsigned int len;
+
+	/* waiting vbuf to be used */
+	while (1) {
+		if (vbuf == virtqueue_get_buf(vq, &len))
+			break;
+	}
+	list_add_tail(&vbuf->list, reclaim_list);
+}
+
+static void virtio_panic_flush(struct drm_plane *plane)
+{
+	struct virtio_gpu_object *bo;
+	struct drm_device *dev = plane->dev;
+	struct virtio_gpu_device *vgdev = dev->dev_private;
+	struct drm_rect rect;
+	struct virtio_gpu_vbuffer_inline *vbuf_inline_dumb_bo;
+	struct virtio_gpu_vbuffer_inline *vbuf_inline_resource_flush;
+
+	vbuf_inline_dumb_bo = virtio_panic_buffer;
+	vbuf_inline_resource_flush = virtio_panic_buffer + VBUFFER_SIZE;
+
+	rect.x1 = 0;
+	rect.y1 = 0;
+	rect.x2 = plane->state->fb->width;
+	rect.y2 = plane->state->fb->height;
+
+	bo = gem_to_virtio_gpu_obj(plane->state->fb->obj[0]);
+
+	struct drm_gem_object obj;
+	struct virtio_gpu_panic_object_array objs = {
+		.next = { NULL, NULL },
+		.nents = 0,
+		.total = 1,
+		.objs = &obj
+	};
+	struct list_head reclaim_list;
+	struct virtio_gpu_vbuffer *entry, *tmp;
+
+	INIT_LIST_HEAD(&reclaim_list);
+
+	if (bo->dumb)
+		virtio_gpu_panic_update_dumb_bo(vgdev,
+						plane->state,
+						&rect,
+						(struct virtio_gpu_object_array *)&objs,
+						&vbuf_inline_dumb_bo->base);
+
+	virtio_gpu_panic_resource_flush(plane, &vbuf_inline_resource_flush->base,
+					plane->state->src_x >> 16,
+					plane->state->src_y >> 16,
+					plane->state->src_w >> 16,
+					plane->state->src_h >> 16);
+	virtio_gpu_panic_notify(vgdev);
+
+	virtio_gpu_panic_get_vbuf(vgdev->ctrlq.vq,
+				  &vbuf_inline_dumb_bo->base,
+				  &reclaim_list);
+	virtio_gpu_panic_get_vbuf(vgdev->ctrlq.vq,
+				  &vbuf_inline_resource_flush->base,
+				  &reclaim_list);
+
+	list_for_each_entry_safe(entry, tmp, &reclaim_list, list) {
+		if (entry->objs)
+			drm_gem_object_put(&objs.objs[0]);
+		list_del(&entry->list);
+	}
+}
+
 static const struct drm_plane_helper_funcs virtio_gpu_primary_helper_funcs = {
 	.prepare_fb		= virtio_gpu_plane_prepare_fb,
 	.cleanup_fb		= virtio_gpu_plane_cleanup_fb,
 	.atomic_check		= virtio_gpu_plane_atomic_check,
 	.atomic_update		= virtio_gpu_primary_plane_update,
+	.get_scanout_buffer	= virtio_drm_get_scanout_buffer,
+	.panic_flush		= virtio_panic_flush,
 };
 
 static const struct drm_plane_helper_funcs virtio_gpu_cursor_helper_funcs = {
@@ -383,6 +537,13 @@ struct drm_plane *virtio_gpu_plane_init(struct virtio_gpu_device *vgdev,
 	const uint32_t *formats;
 	int nformats;
 
+	/* allocate panic buffers */
+	if (index == 0 && type == DRM_PLANE_TYPE_PRIMARY) {
+		virtio_panic_buffer = drmm_kzalloc(dev, 2 * VBUFFER_SIZE, GFP_KERNEL);
+		if (!virtio_panic_buffer)
+			return ERR_PTR(-ENOMEM);
+	}
+
 	if (type == DRM_PLANE_TYPE_CURSOR) {
 		formats = virtio_gpu_cursor_formats;
 		nformats = ARRAY_SIZE(virtio_gpu_cursor_formats);
diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
index 0d3d0d09f39b..b9b8e6a5c314 100644
--- a/drivers/gpu/drm/virtio/virtgpu_vq.c
+++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
@@ -36,12 +36,6 @@
 #include "virtgpu_drv.h"
 #include "virtgpu_trace.h"
 
-#define MAX_INLINE_CMD_SIZE   96
-#define MAX_INLINE_RESP_SIZE  24
-#define VBUFFER_SIZE          (sizeof(struct virtio_gpu_vbuffer) \
-			       + MAX_INLINE_CMD_SIZE		 \
-			       + MAX_INLINE_RESP_SIZE)
-
 static void convert_to_hw_box(struct virtio_gpu_box *dst,
 			      const struct drm_virtgpu_3d_box *src)
 {
@@ -311,6 +305,40 @@ static struct sg_table *vmalloc_to_sgt(char *data, uint32_t size, int *sg_ents)
 	return sgt;
 }
 
+/* For drm_panic */
+static int virtio_gpu_panic_queue_ctrl_sgs(struct virtio_gpu_device *vgdev,
+					   struct virtio_gpu_vbuffer *vbuf,
+					   struct virtio_gpu_fence *fence,
+					   int elemcnt,
+					   struct scatterlist **sgs,
+					   int outcnt,
+					   int incnt)
+{
+	struct virtqueue *vq = vgdev->ctrlq.vq;
+	int ret;
+
+	if (vgdev->has_indirect)
+		elemcnt = 1;
+
+again:
+
+	if (vq->num_free < elemcnt) {
+		virtio_gpu_panic_notify(vgdev);
+		wait_event(vgdev->ctrlq.ack_queue, vq->num_free >= elemcnt);
+		goto again;
+	}
+
+	ret = virtqueue_add_sgs(vq, sgs, outcnt, incnt, vbuf, GFP_ATOMIC);
+	WARN_ON(ret);
+
+	vbuf->seqno = ++vgdev->ctrlq.seqno;
+	trace_virtio_gpu_cmd_queue(vq, virtio_gpu_vbuf_ctrl_hdr(vbuf), vbuf->seqno);
+
+	atomic_inc(&vgdev->pending_commands);
+
+	return 0;
+}
+
 static int virtio_gpu_queue_ctrl_sgs(struct virtio_gpu_device *vgdev,
 				     struct virtio_gpu_vbuffer *vbuf,
 				     struct virtio_gpu_fence *fence,
@@ -368,6 +396,36 @@ static int virtio_gpu_queue_ctrl_sgs(struct virtio_gpu_device *vgdev,
 	return 0;
 }
 
+/* For drm_panic */
+static int virtio_gpu_panic_queue_fenced_ctrl_buffer(struct virtio_gpu_device *vgdev,
+						     struct virtio_gpu_vbuffer *vbuf,
+						     struct virtio_gpu_fence *fence)
+{
+	struct scatterlist *sgs[3], vcmd, vresp;
+	int elemcnt = 0, outcnt = 0, incnt = 0, ret;
+
+	/* set up vcmd */
+	sg_init_one(&vcmd, vbuf->buf, vbuf->size);
+	elemcnt++;
+	sgs[outcnt] = &vcmd;
+	outcnt++;
+
+	/* set up vresp */
+	if (vbuf->resp_size) {
+		sg_init_one(&vresp, vbuf->resp_buf, vbuf->resp_size);
+		elemcnt++;
+		sgs[outcnt + incnt] = &vresp;
+		incnt++;
+	}
+
+	ret = virtio_gpu_panic_queue_ctrl_sgs(vgdev, vbuf,
+					      fence, elemcnt,
+					      sgs, outcnt,
+					      incnt);
+
+	return ret;
+}
+
 static int virtio_gpu_queue_fenced_ctrl_buffer(struct virtio_gpu_device *vgdev,
 					       struct virtio_gpu_vbuffer *vbuf,
 					       struct virtio_gpu_fence *fence)
@@ -422,6 +480,21 @@ static int virtio_gpu_queue_fenced_ctrl_buffer(struct virtio_gpu_device *vgdev,
 	return ret;
 }
 
+/* For drm_panic */
+void virtio_gpu_panic_notify(struct virtio_gpu_device *vgdev)
+{
+	bool notify;
+
+	if (!atomic_read(&vgdev->pending_commands))
+		return;
+
+	atomic_set(&vgdev->pending_commands, 0);
+	notify = virtqueue_kick_prepare(vgdev->ctrlq.vq);
+
+	if (notify)
+		virtqueue_notify(vgdev->ctrlq.vq);
+}
+
 void virtio_gpu_notify(struct virtio_gpu_device *vgdev)
 {
 	bool notify;
@@ -567,6 +640,44 @@ void virtio_gpu_cmd_set_scanout(struct virtio_gpu_device *vgdev,
 	virtio_gpu_queue_ctrl_buffer(vgdev, vbuf);
 }
 
+/* For drm_panic */
+static void virtio_gpu_panic_alloc_cmd(struct virtio_gpu_device *vgdev,
+				       struct virtio_gpu_vbuffer *vbuf,
+				       int cmd_size)
+{
+	vbuf->buf = (void *)vbuf + sizeof(*vbuf);
+	vbuf->size = cmd_size;
+	vbuf->resp_cb = NULL;
+	vbuf->resp_size = sizeof(struct virtio_gpu_ctrl_hdr);
+	vbuf->resp_buf = (void *)vbuf->buf + cmd_size;
+}
+
+/* For drm_panic */
+void virtio_gpu_panic_cmd_resource_flush(struct virtio_gpu_device *vgdev,
+				   struct virtio_gpu_vbuffer *vbuf,
+				   uint32_t resource_id,
+				   uint32_t x, uint32_t y,
+				   uint32_t width, uint32_t height,
+				   struct virtio_gpu_object_array *objs,
+				   struct virtio_gpu_fence *fence)
+{
+	struct virtio_gpu_resource_flush *cmd_p;
+
+	virtio_gpu_panic_alloc_cmd(vgdev, vbuf,
+				   sizeof(struct virtio_gpu_resource_flush));
+	cmd_p = (void *)vbuf->buf;
+	vbuf->objs = objs;
+
+	cmd_p->hdr.type = cpu_to_le32(VIRTIO_GPU_CMD_RESOURCE_FLUSH);
+	cmd_p->resource_id = cpu_to_le32(resource_id);
+	cmd_p->r.width = cpu_to_le32(width);
+	cmd_p->r.height = cpu_to_le32(height);
+	cmd_p->r.x = cpu_to_le32(x);
+	cmd_p->r.y = cpu_to_le32(y);
+
+	virtio_gpu_queue_fenced_ctrl_buffer(vgdev, vbuf, fence);
+}
+
 void virtio_gpu_cmd_resource_flush(struct virtio_gpu_device *vgdev,
 				   uint32_t resource_id,
 				   uint32_t x, uint32_t y,
@@ -591,6 +702,39 @@ void virtio_gpu_cmd_resource_flush(struct virtio_gpu_device *vgdev,
 	virtio_gpu_queue_fenced_ctrl_buffer(vgdev, vbuf, fence);
 }
 
+/* For drm_panic */
+void virtio_gpu_panic_cmd_transfer_to_host_2d(struct virtio_gpu_device *vgdev,
+					      uint64_t offset,
+					      uint32_t width, uint32_t height,
+					      uint32_t x, uint32_t y,
+					      struct virtio_gpu_object_array *objs,
+					      struct virtio_gpu_fence *fence,
+					      struct virtio_gpu_vbuffer *vbuf)
+{
+	struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(objs->objs[0]);
+	struct virtio_gpu_transfer_to_host_2d *cmd_p;
+	bool use_dma_api = !virtio_has_dma_quirk(vgdev->vdev);
+
+	if (virtio_gpu_is_shmem(bo) && use_dma_api)
+		dma_sync_sgtable_for_device(vgdev->vdev->dev.parent,
+					    bo->base.sgt, DMA_TO_DEVICE);
+
+	virtio_gpu_panic_alloc_cmd(vgdev, vbuf,
+				   sizeof(struct virtio_gpu_transfer_to_host_2d));
+	cmd_p = (void *)vbuf->buf;
+	vbuf->objs = objs;
+
+	cmd_p->hdr.type = cpu_to_le32(VIRTIO_GPU_CMD_TRANSFER_TO_HOST_2D);
+	cmd_p->resource_id = cpu_to_le32(bo->hw_res_handle);
+	cmd_p->offset = cpu_to_le64(offset);
+	cmd_p->r.width = cpu_to_le32(width);
+	cmd_p->r.height = cpu_to_le32(height);
+	cmd_p->r.x = cpu_to_le32(x);
+	cmd_p->r.y = cpu_to_le32(y);
+
+	virtio_gpu_panic_queue_fenced_ctrl_buffer(vgdev, vbuf, fence);
+}
+
 void virtio_gpu_cmd_transfer_to_host_2d(struct virtio_gpu_device *vgdev,
 					uint64_t offset,
 					uint32_t width, uint32_t height,
-- 
2.47.0
Re: [PATCH] drm/virtio: Add drm_panic support
Posted by Jocelyn Falempe 3 weeks, 3 days ago
On 31/10/2024 04:20, Ryosuke Yasuoka wrote:
> From: Jocelyn Falempe <jfalempe@redhat.com>
> 
> Virtio gpu supports the drm_panic module, which displays a message to
> the screen when a kernel panic occurs.

Thanks for this patch.
I think a few things can be simplified, see below.
Other than that, it looks good to me.

> 
> Signed-off-by: Ryosuke Yasuoka <ryasuoka@redhat.com>
> Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
> ---
>   drivers/gpu/drm/virtio/virtgpu_drv.h   |  28 +++++
>   drivers/gpu/drm/virtio/virtgpu_plane.c | 161 +++++++++++++++++++++++++
>   drivers/gpu/drm/virtio/virtgpu_vq.c    | 156 +++++++++++++++++++++++-
>   3 files changed, 339 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h b/drivers/gpu/drm/virtio/virtgpu_drv.h
> index 64c236169db8..765698a6dfa3 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_drv.h
> +++ b/drivers/gpu/drm/virtio/virtgpu_drv.h
> @@ -125,7 +125,14 @@ struct virtio_gpu_object_array {
>   	struct drm_gem_object *objs[] __counted_by(total);
>   };
>   
> +#define MAX_INLINE_CMD_SIZE   96
> +#define MAX_INLINE_RESP_SIZE  24
> +#define VBUFFER_SIZE	      (sizeof(struct virtio_gpu_vbuffer) \
> +			      + MAX_INLINE_CMD_SIZE		 \
> +			      + MAX_INLINE_RESP_SIZE)
> +
>   struct virtio_gpu_vbuffer;
> +struct virtio_gpu_vbuffer_inline;

I think virtio_gpu_vbuffer_inline is not used anymore, so you can drop it.

>   struct virtio_gpu_device;
>   
>   typedef void (*virtio_gpu_resp_cb)(struct virtio_gpu_device *vgdev,
> @@ -329,12 +336,26 @@ void virtio_gpu_cmd_create_resource(struct virtio_gpu_device *vgdev,
>   				    struct virtio_gpu_fence *fence);
>   void virtio_gpu_cmd_unref_resource(struct virtio_gpu_device *vgdev,
>   				   struct virtio_gpu_object *bo);
> +void virtio_gpu_panic_cmd_transfer_to_host_2d(struct virtio_gpu_device *vgdev,
> +					      uint64_t offset,
> +					      uint32_t width, uint32_t height,
> +					      uint32_t x, uint32_t y,
> +					      struct virtio_gpu_object_array *objs,
> +					      struct virtio_gpu_fence *fence,
> +					      struct virtio_gpu_vbuffer *vbuf);
>   void virtio_gpu_cmd_transfer_to_host_2d(struct virtio_gpu_device *vgdev,
>   					uint64_t offset,
>   					uint32_t width, uint32_t height,
>   					uint32_t x, uint32_t y,
>   					struct virtio_gpu_object_array *objs,
>   					struct virtio_gpu_fence *fence);
> +void virtio_gpu_panic_cmd_resource_flush(struct virtio_gpu_device *vgdev,
> +					 struct virtio_gpu_vbuffer *vbuf,
> +					 uint32_t resource_id,
> +					 uint32_t x, uint32_t y,
> +					 uint32_t width, uint32_t height,
> +					 struct virtio_gpu_object_array *objs,
> +					 struct virtio_gpu_fence *fence);
>   void virtio_gpu_cmd_resource_flush(struct virtio_gpu_device *vgdev,
>   				   uint32_t resource_id,
>   				   uint32_t x, uint32_t y,
> @@ -399,6 +420,7 @@ void virtio_gpu_ctrl_ack(struct virtqueue *vq);
>   void virtio_gpu_cursor_ack(struct virtqueue *vq);
>   void virtio_gpu_dequeue_ctrl_func(struct work_struct *work);
>   void virtio_gpu_dequeue_cursor_func(struct work_struct *work);
> +void virtio_gpu_panic_notify(struct virtio_gpu_device *vgdev);
>   void virtio_gpu_notify(struct virtio_gpu_device *vgdev);
>   
>   int
> @@ -435,6 +457,12 @@ struct drm_plane *virtio_gpu_plane_init(struct virtio_gpu_device *vgdev,
>   					enum drm_plane_type type,
>   					int index);
>   
> +struct virtio_gpu_vbuffer_inline {
> +	struct virtio_gpu_vbuffer base;
> +	u8 cmd_buf[MAX_INLINE_CMD_SIZE];
> +	u8 resp_buf[MAX_INLINE_RESP_SIZE];
> +};
This struct is no more needed, as the panic vbuffers are pre-allocated 
using VBUFFER_SIZE.

> +
>   /* virtgpu_fence.c */
>   struct virtio_gpu_fence *virtio_gpu_fence_alloc(struct virtio_gpu_device *vgdev,
>   						uint64_t base_fence_ctx,
> diff --git a/drivers/gpu/drm/virtio/virtgpu_plane.c b/drivers/gpu/drm/virtio/virtgpu_plane.c
> index a72a2dbda031..84b65f6b0906 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_plane.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_plane.c
> @@ -26,6 +26,8 @@
>   #include <drm/drm_atomic_helper.h>
>   #include <drm/drm_damage_helper.h>
>   #include <drm/drm_fourcc.h>
> +#include <drm/drm_managed.h>
> +#include <drm/drm_panic.h>
>   
>   #include "virtgpu_drv.h"
>   
> @@ -108,6 +110,28 @@ static int virtio_gpu_plane_atomic_check(struct drm_plane *plane,
>   	return ret;
>   }
>   
> +/* For drm panic */
> +static void virtio_gpu_panic_update_dumb_bo(struct virtio_gpu_device *vgdev,
> +					    struct drm_plane_state *state,
> +					    struct drm_rect *rect,
> +					    struct virtio_gpu_object_array *objs,
> +					    struct virtio_gpu_vbuffer *vbuf)
> +{
> +	struct virtio_gpu_object *bo =
> +		gem_to_virtio_gpu_obj(state->fb->obj[0]);
> +	uint32_t w = rect->x2 - rect->x1;
> +	uint32_t h = rect->y2 - rect->y1;
> +	uint32_t x = rect->x1;
> +	uint32_t y = rect->y1;
> +	uint32_t off = x * state->fb->format->cpp[0] +
> +		y * state->fb->pitches[0];
> +
> +	virtio_gpu_array_add_obj(objs, &bo->base.base);
> +
> +	virtio_gpu_panic_cmd_transfer_to_host_2d(vgdev, off, w, h, x, y,
> +						 objs, NULL, vbuf);
> +}
> +
>   static void virtio_gpu_update_dumb_bo(struct virtio_gpu_device *vgdev,
>   				      struct drm_plane_state *state,
>   				      struct drm_rect *rect)
> @@ -131,6 +155,24 @@ static void virtio_gpu_update_dumb_bo(struct virtio_gpu_device *vgdev,
>   					   objs, NULL);
>   }
>   
> +/* For drm_panic */
> +static void virtio_gpu_panic_resource_flush(struct drm_plane *plane,
> +					    struct virtio_gpu_vbuffer *vbuf,
> +					    uint32_t x, uint32_t y,
> +					    uint32_t width, uint32_t height)
> +{
> +	struct drm_device *dev = plane->dev;
> +	struct virtio_gpu_device *vgdev = dev->dev_private;
> +	struct virtio_gpu_framebuffer *vgfb;
> +	struct virtio_gpu_object *bo;
> +
> +	vgfb = to_virtio_gpu_framebuffer(plane->state->fb);
> +	bo = gem_to_virtio_gpu_obj(vgfb->base.obj[0]);
> +
> +	virtio_gpu_panic_cmd_resource_flush(vgdev, vbuf, bo->hw_res_handle, x, y,
> +					    width, height, NULL, NULL);
> +}
> +
>   static void virtio_gpu_resource_flush(struct drm_plane *plane,
>   				      uint32_t x, uint32_t y,
>   				      uint32_t width, uint32_t height)
> @@ -359,11 +401,123 @@ static void virtio_gpu_cursor_plane_update(struct drm_plane *plane,
>   	virtio_gpu_cursor_ping(vgdev, output);
>   }
>   
> +static int virtio_drm_get_scanout_buffer(struct drm_plane *plane,
> +					 struct drm_scanout_buffer *sb)
> +{
> +	struct virtio_gpu_object *bo;
> +
> +	if (!plane->state || !plane->state->fb || !plane->state->visible)
> +		return -ENODEV;
> +
> +	bo = gem_to_virtio_gpu_obj(plane->state->fb->obj[0]);
> +
> +	/* try to vmap it if possible */
> +	if (!bo->base.vaddr) {
> +		int ret;
> +
> +		ret = drm_gem_shmem_vmap(&bo->base, &sb->map[0]);
> +		if (ret)
> +			return ret;
> +	} else {
> +		iosys_map_set_vaddr(&sb->map[0], bo->base.vaddr);
> +	}
> +
> +	sb->format = plane->state->fb->format;
> +	sb->height = plane->state->fb->height;
> +	sb->width = plane->state->fb->width;
> +	sb->pitch[0] = plane->state->fb->pitches[0];
> +	return 0;
> +}
> +
> +struct virtio_gpu_panic_object_array {
> +	struct ww_acquire_ctx ticket;
> +	struct list_head next;
> +	u32 nents, total;
> +	struct drm_gem_object *objs;
> +};
> +
> +static void *virtio_panic_buffer;
> +
> +static void virtio_gpu_panic_get_vbuf(struct virtqueue *vq,
> +				      struct virtio_gpu_vbuffer *vbuf,
> +				      struct list_head *reclaim_list)
> +{
> +	unsigned int len;
> +
> +	/* waiting vbuf to be used */
> +	while (1) {
> +		if (vbuf == virtqueue_get_buf(vq, &len))
> +			break;
> +	}
> +	list_add_tail(&vbuf->list, reclaim_list);
> +}
Instead of using a reclaim list, I think you can just call 
drm_gem_object_put() if there is an obj here, and that's all.

> +
> +static void virtio_panic_flush(struct drm_plane *plane)
> +{
> +	struct virtio_gpu_object *bo;
> +	struct drm_device *dev = plane->dev;
> +	struct virtio_gpu_device *vgdev = dev->dev_private;
> +	struct drm_rect rect;
> +	struct virtio_gpu_vbuffer_inline *vbuf_inline_dumb_bo;
> +	struct virtio_gpu_vbuffer_inline *vbuf_inline_resource_flush;
I think they should be regular struct virtio_gpu_vbuffer *

> +
> +	vbuf_inline_dumb_bo = virtio_panic_buffer;
> +	vbuf_inline_resource_flush = virtio_panic_buffer + VBUFFER_SIZE;
> +
> +	rect.x1 = 0;
> +	rect.y1 = 0;
> +	rect.x2 = plane->state->fb->width;
> +	rect.y2 = plane->state->fb->height;
> +
> +	bo = gem_to_virtio_gpu_obj(plane->state->fb->obj[0]);
> +
> +	struct drm_gem_object obj;
> +	struct virtio_gpu_panic_object_array objs = {
> +		.next = { NULL, NULL },
> +		.nents = 0,
> +		.total = 1,
> +		.objs = &obj
> +	};
> +	struct list_head reclaim_list;
> +	struct virtio_gpu_vbuffer *entry, *tmp;
> +
> +	INIT_LIST_HEAD(&reclaim_list);
> +
> +	if (bo->dumb)
> +		virtio_gpu_panic_update_dumb_bo(vgdev,
> +						plane->state,
> +						&rect,
> +						(struct virtio_gpu_object_array *)&objs,
> +						&vbuf_inline_dumb_bo->base);
> +
> +	virtio_gpu_panic_resource_flush(plane, &vbuf_inline_resource_flush->base,
> +					plane->state->src_x >> 16,
> +					plane->state->src_y >> 16,
> +					plane->state->src_w >> 16,
> +					plane->state->src_h >> 16);
> +	virtio_gpu_panic_notify(vgdev);
> +
> +	virtio_gpu_panic_get_vbuf(vgdev->ctrlq.vq,
> +				  &vbuf_inline_dumb_bo->base,
> +				  &reclaim_list);
> +	virtio_gpu_panic_get_vbuf(vgdev->ctrlq.vq,
> +				  &vbuf_inline_resource_flush->base,
> +				  &reclaim_list);
> +
> +	list_for_each_entry_safe(entry, tmp, &reclaim_list, list) {
> +		if (entry->objs)
> +			drm_gem_object_put(&objs.objs[0]);
> +		list_del(&entry->list);
> +	}
> +}
> +
>   static const struct drm_plane_helper_funcs virtio_gpu_primary_helper_funcs = {
>   	.prepare_fb		= virtio_gpu_plane_prepare_fb,
>   	.cleanup_fb		= virtio_gpu_plane_cleanup_fb,
>   	.atomic_check		= virtio_gpu_plane_atomic_check,
>   	.atomic_update		= virtio_gpu_primary_plane_update,
> +	.get_scanout_buffer	= virtio_drm_get_scanout_buffer,
> +	.panic_flush		= virtio_panic_flush,
>   };
>   
>   static const struct drm_plane_helper_funcs virtio_gpu_cursor_helper_funcs = {
> @@ -383,6 +537,13 @@ struct drm_plane *virtio_gpu_plane_init(struct virtio_gpu_device *vgdev,
>   	const uint32_t *formats;
>   	int nformats;
>   
> +	/* allocate panic buffers */
> +	if (index == 0 && type == DRM_PLANE_TYPE_PRIMARY) {
> +		virtio_panic_buffer = drmm_kzalloc(dev, 2 * VBUFFER_SIZE, GFP_KERNEL);
> +		if (!virtio_panic_buffer)
> +			return ERR_PTR(-ENOMEM);
> +	}
> +
>   	if (type == DRM_PLANE_TYPE_CURSOR) {
>   		formats = virtio_gpu_cursor_formats;
>   		nformats = ARRAY_SIZE(virtio_gpu_cursor_formats);
> diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
> index 0d3d0d09f39b..b9b8e6a5c314 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_vq.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
> @@ -36,12 +36,6 @@
>   #include "virtgpu_drv.h"
>   #include "virtgpu_trace.h"
>   
> -#define MAX_INLINE_CMD_SIZE   96
> -#define MAX_INLINE_RESP_SIZE  24
> -#define VBUFFER_SIZE          (sizeof(struct virtio_gpu_vbuffer) \
> -			       + MAX_INLINE_CMD_SIZE		 \
> -			       + MAX_INLINE_RESP_SIZE)
> -
>   static void convert_to_hw_box(struct virtio_gpu_box *dst,
>   			      const struct drm_virtgpu_3d_box *src)
>   {
> @@ -311,6 +305,40 @@ static struct sg_table *vmalloc_to_sgt(char *data, uint32_t size, int *sg_ents)
>   	return sgt;
>   }
>   
> +/* For drm_panic */
> +static int virtio_gpu_panic_queue_ctrl_sgs(struct virtio_gpu_device *vgdev,
> +					   struct virtio_gpu_vbuffer *vbuf,
> +					   struct virtio_gpu_fence *fence,
fence is always NULL, so you can remove it from the arguments.

> +					   int elemcnt,
> +					   struct scatterlist **sgs,
> +					   int outcnt,
> +					   int incnt)
> +{
> +	struct virtqueue *vq = vgdev->ctrlq.vq;
> +	int ret;
> +
> +	if (vgdev->has_indirect)
> +		elemcnt = 1;
> +
> +again:
> +
> +	if (vq->num_free < elemcnt) {
> +		virtio_gpu_panic_notify(vgdev);
> +		wait_event(vgdev->ctrlq.ack_queue, vq->num_free >= elemcnt);
In a panic handler, it can't wait for an event. If the virtio queue is 
full, maybe just return an error, and no panic message would be seen.

> +		goto again;
> +	}
> +
> +	ret = virtqueue_add_sgs(vq, sgs, outcnt, incnt, vbuf, GFP_ATOMIC);
> +	WARN_ON(ret);
> +
> +	vbuf->seqno = ++vgdev->ctrlq.seqno;
> +	trace_virtio_gpu_cmd_queue(vq, virtio_gpu_vbuf_ctrl_hdr(vbuf), vbuf->seqno);
> +
> +	atomic_inc(&vgdev->pending_commands);
> +
> +	return 0;
> +}
> +
>   static int virtio_gpu_queue_ctrl_sgs(struct virtio_gpu_device *vgdev,
>   				     struct virtio_gpu_vbuffer *vbuf,
>   				     struct virtio_gpu_fence *fence,
> @@ -368,6 +396,36 @@ static int virtio_gpu_queue_ctrl_sgs(struct virtio_gpu_device *vgdev,
>   	return 0;
>   }
>   
> +/* For drm_panic */
> +static int virtio_gpu_panic_queue_fenced_ctrl_buffer(struct virtio_gpu_device *vgdev,
> +						     struct virtio_gpu_vbuffer *vbuf,
> +						     struct virtio_gpu_fence *fence)
fence is always NULL when calling this, so you can remove it from the 
arguments, and remove the "fenced" from the function name.
> +{
> +	struct scatterlist *sgs[3], vcmd, vresp;
> +	int elemcnt = 0, outcnt = 0, incnt = 0, ret;
> +
> +	/* set up vcmd */
> +	sg_init_one(&vcmd, vbuf->buf, vbuf->size);
> +	elemcnt++;
> +	sgs[outcnt] = &vcmd;
> +	outcnt++;
> +
> +	/* set up vresp */
> +	if (vbuf->resp_size) {
> +		sg_init_one(&vresp, vbuf->resp_buf, vbuf->resp_size);
> +		elemcnt++;
> +		sgs[outcnt + incnt] = &vresp;
> +		incnt++;
> +	}
> +
> +	ret = virtio_gpu_panic_queue_ctrl_sgs(vgdev, vbuf,
> +					      fence, elemcnt,
> +					      sgs, outcnt,
> +					      incnt);
> +
> +	return ret;
> +}
> +
>   static int virtio_gpu_queue_fenced_ctrl_buffer(struct virtio_gpu_device *vgdev,
>   					       struct virtio_gpu_vbuffer *vbuf,
>   					       struct virtio_gpu_fence *fence)
> @@ -422,6 +480,21 @@ static int virtio_gpu_queue_fenced_ctrl_buffer(struct virtio_gpu_device *vgdev,
>   	return ret;
>   }
>   
> +/* For drm_panic */
> +void virtio_gpu_panic_notify(struct virtio_gpu_device *vgdev)
> +{
> +	bool notify;
> +
> +	if (!atomic_read(&vgdev->pending_commands))
> +		return;
> +
> +	atomic_set(&vgdev->pending_commands, 0);
> +	notify = virtqueue_kick_prepare(vgdev->ctrlq.vq);
> +
> +	if (notify)
> +		virtqueue_notify(vgdev->ctrlq.vq);
> +}
> +
>   void virtio_gpu_notify(struct virtio_gpu_device *vgdev)
>   {
>   	bool notify;
> @@ -567,6 +640,44 @@ void virtio_gpu_cmd_set_scanout(struct virtio_gpu_device *vgdev,
>   	virtio_gpu_queue_ctrl_buffer(vgdev, vbuf);
>   }
>   
> +/* For drm_panic */
> +static void virtio_gpu_panic_alloc_cmd(struct virtio_gpu_device *vgdev,
> +				       struct virtio_gpu_vbuffer *vbuf,
> +				       int cmd_size)
> +{
> +	vbuf->buf = (void *)vbuf + sizeof(*vbuf);
> +	vbuf->size = cmd_size;
> +	vbuf->resp_cb = NULL;
> +	vbuf->resp_size = sizeof(struct virtio_gpu_ctrl_hdr);
> +	vbuf->resp_buf = (void *)vbuf->buf + cmd_size;
> +}
I think you can rename this to virtio_gpu_panic_init_cmd, because we're 
not allocating a buffer, just initializing a pre-allocated buffer.

> +
> +/* For drm_panic */
> +void virtio_gpu_panic_cmd_resource_flush(struct virtio_gpu_device *vgdev,
> +				   struct virtio_gpu_vbuffer *vbuf,
> +				   uint32_t resource_id,
> +				   uint32_t x, uint32_t y,
> +				   uint32_t width, uint32_t height,
> +				   struct virtio_gpu_object_array *objs,
> +				   struct virtio_gpu_fence *fence)
objs and fence are always NULL, so you can remove them from the arguments.

> +{
> +	struct virtio_gpu_resource_flush *cmd_p;
> +
> +	virtio_gpu_panic_alloc_cmd(vgdev, vbuf,
> +				   sizeof(struct virtio_gpu_resource_flush));
> +	cmd_p = (void *)vbuf->buf;
> +	vbuf->objs = objs;
> +
> +	cmd_p->hdr.type = cpu_to_le32(VIRTIO_GPU_CMD_RESOURCE_FLUSH);
> +	cmd_p->resource_id = cpu_to_le32(resource_id);
> +	cmd_p->r.width = cpu_to_le32(width);
> +	cmd_p->r.height = cpu_to_le32(height);
> +	cmd_p->r.x = cpu_to_le32(x);
> +	cmd_p->r.y = cpu_to_le32(y);
> +
> +	virtio_gpu_queue_fenced_ctrl_buffer(vgdev, vbuf, fence);
Use virtio_gpu_panic_queue_fenced_ctrl_buffer() there ?
> +}
> +
>   void virtio_gpu_cmd_resource_flush(struct virtio_gpu_device *vgdev,
>   				   uint32_t resource_id,
>   				   uint32_t x, uint32_t y,
> @@ -591,6 +702,39 @@ void virtio_gpu_cmd_resource_flush(struct virtio_gpu_device *vgdev,
>   	virtio_gpu_queue_fenced_ctrl_buffer(vgdev, vbuf, fence);
>   }
>   
> +/* For drm_panic */
> +void virtio_gpu_panic_cmd_transfer_to_host_2d(struct virtio_gpu_device *vgdev,
> +					      uint64_t offset,
> +					      uint32_t width, uint32_t height,
> +					      uint32_t x, uint32_t y,
> +					      struct virtio_gpu_object_array *objs,
> +					      struct virtio_gpu_fence *fence,
> +					      struct virtio_gpu_vbuffer *vbuf)
fence is always NULL when calling this function, so you can remove it 
from the arguments.

> +{
> +	struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(objs->objs[0]);
> +	struct virtio_gpu_transfer_to_host_2d *cmd_p;
> +	bool use_dma_api = !virtio_has_dma_quirk(vgdev->vdev);
> +
> +	if (virtio_gpu_is_shmem(bo) && use_dma_api)
> +		dma_sync_sgtable_for_device(vgdev->vdev->dev.parent,
> +					    bo->base.sgt, DMA_TO_DEVICE);
> +
> +	virtio_gpu_panic_alloc_cmd(vgdev, vbuf,
> +				   sizeof(struct virtio_gpu_transfer_to_host_2d));
> +	cmd_p = (void *)vbuf->buf;
> +	vbuf->objs = objs;
> +
> +	cmd_p->hdr.type = cpu_to_le32(VIRTIO_GPU_CMD_TRANSFER_TO_HOST_2D);
> +	cmd_p->resource_id = cpu_to_le32(bo->hw_res_handle);
> +	cmd_p->offset = cpu_to_le64(offset);
> +	cmd_p->r.width = cpu_to_le32(width);
> +	cmd_p->r.height = cpu_to_le32(height);
> +	cmd_p->r.x = cpu_to_le32(x);
> +	cmd_p->r.y = cpu_to_le32(y);
> +
> +	virtio_gpu_panic_queue_fenced_ctrl_buffer(vgdev, vbuf, fence);
> +}
> +
>   void virtio_gpu_cmd_transfer_to_host_2d(struct virtio_gpu_device *vgdev,
>   					uint64_t offset,
>   					uint32_t width, uint32_t height,