[PATCH v2 0/2] Add sync object UAPI support to VirtIO-GPU driver

[PATCH v2 0/2] Add sync object UAPI support to VirtIO-GPU driver

[Dmitry Osipenko]

We have multiple Vulkan context types that are awaiting for the addition
of the sync object DRM UAPI support to the VirtIO-GPU kernel driver:

 1. Venus context
 2. Native contexts (virtio-freedreno, virtio-intel, virtio-amdgpu)

Mesa core supports DRM sync object UAPI, providing Vulkan drivers with a
generic fencing implementation that we want to utilize.

This patch adds initial sync objects support. It creates fundament for a
further fencing improvements. Later on we will want to extend the VirtIO-GPU
fencing API with passing fence IDs to host for waiting, it will be a new
additional VirtIO-GPU IOCTL and more. Today we have several VirtIO-GPU context
drivers in works that require VirtIO-GPU to support sync objects UAPI.

The patch is heavily inspired by the sync object UAPI implementation of the
MSM driver.

Changelog:

v2: - Fixed chain-fence context matching by making use of
      dma_fence_chain_contained().

    - Fixed potential uninitialized var usage in error code patch of
      parse_post_deps(). MSM driver had a similar issue that is fixed
      already in upstream.

    - Added new patch that refactors job submission code path. I found
      that it was very difficult to add a new/upcoming host-waits feature
      because of how variables are passed around the code, the virtgpu_ioctl.c
      also was growing to unmanageable size.

Dmitry Osipenko (2):
  drm/virtio: Refactor job submission code path
  drm/virtio: Support sync objects

 drivers/gpu/drm/virtio/Makefile         |   2 +-
 drivers/gpu/drm/virtio/virtgpu_drv.c    |   3 +-
 drivers/gpu/drm/virtio/virtgpu_drv.h    |   4 +
 drivers/gpu/drm/virtio/virtgpu_ioctl.c  | 182 ---------
 drivers/gpu/drm/virtio/virtgpu_submit.c | 510 ++++++++++++++++++++++++
 include/uapi/drm/virtgpu_drm.h          |  16 +-
 6 files changed, 532 insertions(+), 185 deletions(-)
 create mode 100644 drivers/gpu/drm/virtio/virtgpu_submit.c

-- 
2.39.2

[PATCH v2 1/2] drm/virtio: Refactor job submission code path

[Dmitry Osipenko]

Move virtio_gpu_execbuffer_ioctl() into separate virtgpu_submit.c file
and refactor the code along the way to ease addition of new features to
the ioctl.

Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
 drivers/gpu/drm/virtio/Makefile         |   2 +-
 drivers/gpu/drm/virtio/virtgpu_drv.h    |   4 +
 drivers/gpu/drm/virtio/virtgpu_ioctl.c  | 182 ---------------
 drivers/gpu/drm/virtio/virtgpu_submit.c | 298 ++++++++++++++++++++++++
 4 files changed, 303 insertions(+), 183 deletions(-)
 create mode 100644 drivers/gpu/drm/virtio/virtgpu_submit.c

diff --git a/drivers/gpu/drm/virtio/Makefile b/drivers/gpu/drm/virtio/Makefile
index b99fa4a73b68..d2e1788a8227 100644
--- a/drivers/gpu/drm/virtio/Makefile
+++ b/drivers/gpu/drm/virtio/Makefile
@@ -6,6 +6,6 @@
 virtio-gpu-y := virtgpu_drv.o virtgpu_kms.o virtgpu_gem.o virtgpu_vram.o \
 	virtgpu_display.o virtgpu_vq.o \
 	virtgpu_fence.o virtgpu_object.o virtgpu_debugfs.o virtgpu_plane.o \
-	virtgpu_ioctl.o virtgpu_prime.o virtgpu_trace_points.o
+	virtgpu_ioctl.o virtgpu_prime.o virtgpu_trace_points.o virtgpu_submit.o
 
 obj-$(CONFIG_DRM_VIRTIO_GPU) += virtio-gpu.o
diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h b/drivers/gpu/drm/virtio/virtgpu_drv.h
index af6ffb696086..4126c384286b 100644
--- a/drivers/gpu/drm/virtio/virtgpu_drv.h
+++ b/drivers/gpu/drm/virtio/virtgpu_drv.h
@@ -486,4 +486,8 @@ void virtio_gpu_vram_unmap_dma_buf(struct device *dev,
 				   struct sg_table *sgt,
 				   enum dma_data_direction dir);
 
+/* virtgpu_submit.c */
+int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
+				struct drm_file *file);
+
 #endif
diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
index da45215a933d..b24b11f25197 100644
--- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
+++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
@@ -38,36 +38,6 @@
 				    VIRTGPU_BLOB_FLAG_USE_SHAREABLE | \
 				    VIRTGPU_BLOB_FLAG_USE_CROSS_DEVICE)
 
-static int virtio_gpu_fence_event_create(struct drm_device *dev,
-					 struct drm_file *file,
-					 struct virtio_gpu_fence *fence,
-					 uint32_t ring_idx)
-{
-	struct virtio_gpu_fpriv *vfpriv = file->driver_priv;
-	struct virtio_gpu_fence_event *e = NULL;
-	int ret;
-
-	if (!(vfpriv->ring_idx_mask & BIT_ULL(ring_idx)))
-		return 0;
-
-	e = kzalloc(sizeof(*e), GFP_KERNEL);
-	if (!e)
-		return -ENOMEM;
-
-	e->event.type = VIRTGPU_EVENT_FENCE_SIGNALED;
-	e->event.length = sizeof(e->event);
-
-	ret = drm_event_reserve_init(dev, file, &e->base, &e->event);
-	if (ret)
-		goto free;
-
-	fence->e = e;
-	return 0;
-free:
-	kfree(e);
-	return ret;
-}
-
 /* Must be called with &virtio_gpu_fpriv.struct_mutex held. */
 static void virtio_gpu_create_context_locked(struct virtio_gpu_device *vgdev,
 					     struct virtio_gpu_fpriv *vfpriv)
@@ -108,158 +78,6 @@ static int virtio_gpu_map_ioctl(struct drm_device *dev, void *data,
 					 &virtio_gpu_map->offset);
 }
 
-/*
- * Usage of execbuffer:
- * Relocations need to take into account the full VIRTIO_GPUDrawable size.
- * However, the command as passed from user space must *not* contain the initial
- * VIRTIO_GPUReleaseInfo struct (first XXX bytes)
- */
-static int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
-				 struct drm_file *file)
-{
-	struct drm_virtgpu_execbuffer *exbuf = data;
-	struct virtio_gpu_device *vgdev = dev->dev_private;
-	struct virtio_gpu_fpriv *vfpriv = file->driver_priv;
-	struct virtio_gpu_fence *out_fence;
-	int ret;
-	uint32_t *bo_handles = NULL;
-	void __user *user_bo_handles = NULL;
-	struct virtio_gpu_object_array *buflist = NULL;
-	struct sync_file *sync_file;
-	int out_fence_fd = -1;
-	void *buf;
-	uint64_t fence_ctx;
-	uint32_t ring_idx;
-
-	fence_ctx = vgdev->fence_drv.context;
-	ring_idx = 0;
-
-	if (vgdev->has_virgl_3d == false)
-		return -ENOSYS;
-
-	if ((exbuf->flags & ~VIRTGPU_EXECBUF_FLAGS))
-		return -EINVAL;
-
-	if ((exbuf->flags & VIRTGPU_EXECBUF_RING_IDX)) {
-		if (exbuf->ring_idx >= vfpriv->num_rings)
-			return -EINVAL;
-
-		if (!vfpriv->base_fence_ctx)
-			return -EINVAL;
-
-		fence_ctx = vfpriv->base_fence_ctx;
-		ring_idx = exbuf->ring_idx;
-	}
-
-	virtio_gpu_create_context(dev, file);
-	if (exbuf->flags & VIRTGPU_EXECBUF_FENCE_FD_IN) {
-		struct dma_fence *in_fence;
-
-		in_fence = sync_file_get_fence(exbuf->fence_fd);
-
-		if (!in_fence)
-			return -EINVAL;
-
-		/*
-		 * Wait if the fence is from a foreign context, or if the fence
-		 * array contains any fence from a foreign context.
-		 */
-		ret = 0;
-		if (!dma_fence_match_context(in_fence, fence_ctx + ring_idx))
-			ret = dma_fence_wait(in_fence, true);
-
-		dma_fence_put(in_fence);
-		if (ret)
-			return ret;
-	}
-
-	if (exbuf->flags & VIRTGPU_EXECBUF_FENCE_FD_OUT) {
-		out_fence_fd = get_unused_fd_flags(O_CLOEXEC);
-		if (out_fence_fd < 0)
-			return out_fence_fd;
-	}
-
-	if (exbuf->num_bo_handles) {
-		bo_handles = kvmalloc_array(exbuf->num_bo_handles,
-					    sizeof(uint32_t), GFP_KERNEL);
-		if (!bo_handles) {
-			ret = -ENOMEM;
-			goto out_unused_fd;
-		}
-
-		user_bo_handles = u64_to_user_ptr(exbuf->bo_handles);
-		if (copy_from_user(bo_handles, user_bo_handles,
-				   exbuf->num_bo_handles * sizeof(uint32_t))) {
-			ret = -EFAULT;
-			goto out_unused_fd;
-		}
-
-		buflist = virtio_gpu_array_from_handles(file, bo_handles,
-							exbuf->num_bo_handles);
-		if (!buflist) {
-			ret = -ENOENT;
-			goto out_unused_fd;
-		}
-		kvfree(bo_handles);
-		bo_handles = NULL;
-	}
-
-	buf = vmemdup_user(u64_to_user_ptr(exbuf->command), exbuf->size);
-	if (IS_ERR(buf)) {
-		ret = PTR_ERR(buf);
-		goto out_unused_fd;
-	}
-
-	if (buflist) {
-		ret = virtio_gpu_array_lock_resv(buflist);
-		if (ret)
-			goto out_memdup;
-	}
-
-	out_fence = virtio_gpu_fence_alloc(vgdev, fence_ctx, ring_idx);
-	if(!out_fence) {
-		ret = -ENOMEM;
-		goto out_unresv;
-	}
-
-	ret = virtio_gpu_fence_event_create(dev, file, out_fence, ring_idx);
-	if (ret)
-		goto out_unresv;
-
-	if (out_fence_fd >= 0) {
-		sync_file = sync_file_create(&out_fence->f);
-		if (!sync_file) {
-			dma_fence_put(&out_fence->f);
-			ret = -ENOMEM;
-			goto out_unresv;
-		}
-
-		exbuf->fence_fd = out_fence_fd;
-		fd_install(out_fence_fd, sync_file->file);
-	}
-
-	virtio_gpu_cmd_submit(vgdev, buf, exbuf->size,
-			      vfpriv->ctx_id, buflist, out_fence);
-	dma_fence_put(&out_fence->f);
-	virtio_gpu_notify(vgdev);
-	return 0;
-
-out_unresv:
-	if (buflist)
-		virtio_gpu_array_unlock_resv(buflist);
-out_memdup:
-	kvfree(buf);
-out_unused_fd:
-	kvfree(bo_handles);
-	if (buflist)
-		virtio_gpu_array_put_free(buflist);
-
-	if (out_fence_fd >= 0)
-		put_unused_fd(out_fence_fd);
-
-	return ret;
-}
-
 static int virtio_gpu_getparam_ioctl(struct drm_device *dev, void *data,
 				     struct drm_file *file)
 {
diff --git a/drivers/gpu/drm/virtio/virtgpu_submit.c b/drivers/gpu/drm/virtio/virtgpu_submit.c
new file mode 100644
index 000000000000..a96f9d3285c7
--- /dev/null
+++ b/drivers/gpu/drm/virtio/virtgpu_submit.c
@@ -0,0 +1,298 @@
+// SPDX-License-Identifier: MIT
+/*
+ * Copyright (C) 2015 Red Hat, Inc.
+ * All Rights Reserved.
+ *
+ * Authors:
+ *    Dave Airlie
+ *    Alon Levy
+ */
+
+#include <linux/file.h>
+#include <linux/sync_file.h>
+#include <linux/uaccess.h>
+
+#include <drm/drm_file.h>
+#include <drm/virtgpu_drm.h>
+
+#include "virtgpu_drv.h"
+
+struct virtio_gpu_submit {
+	struct virtio_gpu_object_array *buflist;
+	struct drm_virtgpu_execbuffer *exbuf;
+	struct virtio_gpu_fence *out_fence;
+	struct virtio_gpu_fpriv *vfpriv;
+	struct virtio_gpu_device *vgdev;
+	struct drm_file *file;
+	uint64_t fence_ctx;
+	uint32_t ring_idx;
+	int out_fence_fd;
+	void *buf;
+};
+
+static int virtio_gpu_do_fence_wait(struct virtio_gpu_submit *submit,
+				    struct dma_fence *dma_fence)
+{
+	uint32_t context = submit->fence_ctx + submit->ring_idx;
+
+	if (dma_fence_match_context(dma_fence, context))
+		return 0;
+
+	return dma_fence_wait(dma_fence, true);
+}
+
+static int virtio_gpu_dma_fence_wait(struct virtio_gpu_submit *submit,
+				     struct dma_fence *fence)
+{
+	struct dma_fence *itr;
+	int idx, err;
+
+	dma_fence_array_for_each(itr, idx, fence) {
+		err = virtio_gpu_do_fence_wait(submit, itr);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
+static int virtio_gpu_fence_event_create(struct drm_device *dev,
+					 struct drm_file *file,
+					 struct virtio_gpu_fence *fence,
+					 uint32_t ring_idx)
+{
+	struct virtio_gpu_fpriv *vfpriv = file->driver_priv;
+	struct virtio_gpu_fence_event *e = NULL;
+	int ret;
+
+	if (!(vfpriv->ring_idx_mask & BIT_ULL(ring_idx)))
+		return 0;
+
+	e = kzalloc(sizeof(*e), GFP_KERNEL);
+	if (!e)
+		return -ENOMEM;
+
+	e->event.type = VIRTGPU_EVENT_FENCE_SIGNALED;
+	e->event.length = sizeof(e->event);
+
+	ret = drm_event_reserve_init(dev, file, &e->base, &e->event);
+	if (ret) {
+		kfree(e);
+		return ret;
+	}
+
+	fence->e = e;
+
+	return 0;
+}
+
+static int virtio_gpu_init_submit_buflist(struct virtio_gpu_submit *submit)
+{
+	struct drm_virtgpu_execbuffer *exbuf = submit->exbuf;
+	uint32_t *bo_handles;
+
+	if (!exbuf->num_bo_handles)
+		return 0;
+
+	bo_handles = kvmalloc_array(exbuf->num_bo_handles, sizeof(uint32_t),
+				    GFP_KERNEL);
+	if (!bo_handles)
+		return -ENOMEM;
+
+	if (copy_from_user(bo_handles, u64_to_user_ptr(exbuf->bo_handles),
+			   exbuf->num_bo_handles * sizeof(uint32_t))) {
+		kvfree(bo_handles);
+		return -EFAULT;
+	}
+
+	submit->buflist = virtio_gpu_array_from_handles(submit->file, bo_handles,
+							exbuf->num_bo_handles);
+	if (!submit->buflist) {
+		kvfree(bo_handles);
+		return -ENOENT;
+	}
+
+	kvfree(bo_handles);
+
+	return 0;
+}
+
+static void virtio_gpu_cleanup_submit(struct virtio_gpu_submit *submit)
+{
+	if (!IS_ERR(submit->buf))
+		kvfree(submit->buf);
+
+	if (submit->buflist)
+		virtio_gpu_array_put_free(submit->buflist);
+
+	if (submit->out_fence_fd >= 0)
+		put_unused_fd(submit->out_fence_fd);
+}
+
+static void virtio_gpu_submit(struct virtio_gpu_submit *submit)
+{
+	virtio_gpu_cmd_submit(submit->vgdev, submit->buf, submit->exbuf->size,
+			      submit->vfpriv->ctx_id, submit->buflist,
+			      submit->out_fence);
+	virtio_gpu_notify(submit->vgdev);
+
+	submit->buf = NULL;
+	submit->buflist = NULL;
+	submit->out_fence_fd = -1;
+}
+
+static int virtio_gpu_init_submit(struct virtio_gpu_submit *submit,
+				  struct drm_virtgpu_execbuffer *exbuf,
+				  struct drm_device *dev,
+				  struct drm_file *file,
+				  uint64_t fence_ctx, uint32_t ring_idx)
+{
+	struct virtio_gpu_fpriv *vfpriv = file->driver_priv;
+	struct virtio_gpu_device *vgdev = dev->dev_private;
+	struct virtio_gpu_fence *out_fence;
+	int err;
+
+	memset(submit, 0, sizeof(*submit));
+
+	out_fence = virtio_gpu_fence_alloc(vgdev, fence_ctx, ring_idx);
+	if (!out_fence)
+		return -ENOMEM;
+
+	err = virtio_gpu_fence_event_create(dev, file, out_fence, ring_idx);
+	if (err) {
+		dma_fence_put(&out_fence->f);
+		return err;
+	}
+
+	submit->out_fence = out_fence;
+	submit->fence_ctx = fence_ctx;
+	submit->ring_idx = ring_idx;
+	submit->out_fence_fd = -1;
+	submit->vfpriv = vfpriv;
+	submit->vgdev = vgdev;
+	submit->exbuf = exbuf;
+	submit->file = file;
+
+	err = virtio_gpu_init_submit_buflist(submit);
+	if (err)
+		return err;
+
+	submit->buf = vmemdup_user(u64_to_user_ptr(exbuf->command), exbuf->size);
+	if (IS_ERR(submit->buf))
+		return PTR_ERR(submit->buf);
+
+	if (exbuf->flags & VIRTGPU_EXECBUF_FENCE_FD_OUT) {
+		err = get_unused_fd_flags(O_CLOEXEC);
+		if (err < 0)
+			return err;
+
+		submit->out_fence_fd = err;
+	}
+
+	return 0;
+}
+
+static int virtio_gpu_wait_in_fence(struct virtio_gpu_submit *submit)
+{
+	int ret = 0;
+
+	if (submit->exbuf->flags & VIRTGPU_EXECBUF_FENCE_FD_IN) {
+		struct dma_fence *in_fence =
+				sync_file_get_fence(submit->exbuf->fence_fd);
+		if (!in_fence)
+			return -EINVAL;
+
+		/*
+		 * Wait if the fence is from a foreign context, or if the fence
+		 * array contains any fence from a foreign context.
+		 */
+		ret = virtio_gpu_dma_fence_wait(submit, in_fence);
+
+		dma_fence_put(in_fence);
+	}
+
+	return ret;
+}
+
+static int virtio_gpu_install_out_fence_fd(struct virtio_gpu_submit *submit)
+{
+	if (submit->out_fence_fd >= 0) {
+		struct sync_file *sync_file =
+					sync_file_create(&submit->out_fence->f);
+		if (!sync_file)
+			return -ENOMEM;
+
+		submit->exbuf->fence_fd = submit->out_fence_fd;
+		fd_install(submit->out_fence_fd, sync_file->file);
+	}
+
+	return 0;
+}
+
+static int virtio_gpu_lock_buflist(struct virtio_gpu_submit *submit)
+{
+	if (submit->buflist)
+		return virtio_gpu_array_lock_resv(submit->buflist);
+
+	return 0;
+}
+
+/*
+ * Usage of execbuffer:
+ * Relocations need to take into account the full VIRTIO_GPUDrawable size.
+ * However, the command as passed from user space must *not* contain the initial
+ * VIRTIO_GPUReleaseInfo struct (first XXX bytes)
+ */
+int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
+				struct drm_file *file)
+{
+	struct virtio_gpu_device *vgdev = dev->dev_private;
+	struct virtio_gpu_fpriv *vfpriv = file->driver_priv;
+	uint64_t fence_ctx = vgdev->fence_drv.context;
+	struct drm_virtgpu_execbuffer *exbuf = data;
+	struct virtio_gpu_submit submit;
+	uint32_t ring_idx = 0;
+	int ret = -EINVAL;
+
+	if (vgdev->has_virgl_3d == false)
+		return -ENOSYS;
+
+	if ((exbuf->flags & ~VIRTGPU_EXECBUF_FLAGS))
+		return ret;
+
+	if ((exbuf->flags & VIRTGPU_EXECBUF_RING_IDX)) {
+		if (exbuf->ring_idx >= vfpriv->num_rings)
+			return ret;
+
+		if (!vfpriv->base_fence_ctx)
+			return ret;
+
+		fence_ctx = vfpriv->base_fence_ctx;
+		ring_idx = exbuf->ring_idx;
+	}
+
+	virtio_gpu_create_context(dev, file);
+
+	ret = virtio_gpu_init_submit(&submit, exbuf, dev, file,
+				     fence_ctx, ring_idx);
+	if (ret)
+		goto cleanup;
+
+	ret = virtio_gpu_wait_in_fence(&submit);
+	if (ret)
+		goto cleanup;
+
+	ret = virtio_gpu_install_out_fence_fd(&submit);
+	if (ret)
+		goto cleanup;
+
+	ret = virtio_gpu_lock_buflist(&submit);
+	if (ret)
+		goto cleanup;
+
+	virtio_gpu_submit(&submit);
+cleanup:
+	virtio_gpu_cleanup_submit(&submit);
+
+	return ret;
+}
-- 
2.39.2

[PATCH v2 2/2] drm/virtio: Support sync objects

[Dmitry Osipenko]

Add sync object DRM UAPI support to VirtIO-GPU driver. It's required
for enabling a full-featured Vulkan fencing by Venus and native context
VirtIO-GPU Mesa drivers.

Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
 drivers/gpu/drm/virtio/virtgpu_drv.c    |   3 +-
 drivers/gpu/drm/virtio/virtgpu_submit.c | 214 +++++++++++++++++++++++-
 include/uapi/drm/virtgpu_drm.h          |  16 +-
 3 files changed, 230 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.c b/drivers/gpu/drm/virtio/virtgpu_drv.c
index add075681e18..a22155577152 100644
--- a/drivers/gpu/drm/virtio/virtgpu_drv.c
+++ b/drivers/gpu/drm/virtio/virtgpu_drv.c
@@ -176,7 +176,8 @@ static const struct drm_driver driver = {
 	 * If KMS is disabled DRIVER_MODESET and DRIVER_ATOMIC are masked
 	 * out via drm_device::driver_features:
 	 */
-	.driver_features = DRIVER_MODESET | DRIVER_GEM | DRIVER_RENDER | DRIVER_ATOMIC,
+	.driver_features = DRIVER_MODESET | DRIVER_GEM | DRIVER_RENDER | DRIVER_ATOMIC |
+			   DRIVER_SYNCOBJ | DRIVER_SYNCOBJ_TIMELINE,
 	.open = virtio_gpu_driver_open,
 	.postclose = virtio_gpu_driver_postclose,
 
diff --git a/drivers/gpu/drm/virtio/virtgpu_submit.c b/drivers/gpu/drm/virtio/virtgpu_submit.c
index a96f9d3285c7..eb29c4e72dd1 100644
--- a/drivers/gpu/drm/virtio/virtgpu_submit.c
+++ b/drivers/gpu/drm/virtio/virtgpu_submit.c
@@ -13,11 +13,26 @@
 #include <linux/uaccess.h>
 
 #include <drm/drm_file.h>
+#include <drm/drm_syncobj.h>
 #include <drm/virtgpu_drm.h>
 
 #include "virtgpu_drv.h"
 
+struct virtio_gpu_submit_post_dep {
+	struct drm_syncobj *syncobj;
+	struct dma_fence_chain *chain;
+	uint64_t point;
+};
+
 struct virtio_gpu_submit {
+	struct virtio_gpu_submit_post_dep *post_deps;
+	unsigned int num_out_syncobjs;
+
+	struct drm_syncobj **in_syncobjs;
+	unsigned int num_in_syncobjs;
+	uint64_t *in_fence_ids;
+	unsigned int num_in_fence_ids;
+
 	struct virtio_gpu_object_array *buflist;
 	struct drm_virtgpu_execbuffer *exbuf;
 	struct virtio_gpu_fence *out_fence;
@@ -33,9 +48,10 @@ struct virtio_gpu_submit {
 static int virtio_gpu_do_fence_wait(struct virtio_gpu_submit *submit,
 				    struct dma_fence *dma_fence)
 {
+	struct dma_fence *in_fence = dma_fence_chain_contained(dma_fence);
 	uint32_t context = submit->fence_ctx + submit->ring_idx;
 
-	if (dma_fence_match_context(dma_fence, context))
+	if (dma_fence_match_context(in_fence, context))
 		return 0;
 
 	return dma_fence_wait(dma_fence, true);
@@ -56,6 +72,186 @@ static int virtio_gpu_dma_fence_wait(struct virtio_gpu_submit *submit,
 	return 0;
 }
 
+static void virtio_gpu_free_syncobjs(struct drm_syncobj **syncobjs,
+				     uint32_t nr_syncobjs)
+{
+	uint32_t i = nr_syncobjs;
+
+	while (syncobjs && i--) {
+		if (syncobjs[i])
+			drm_syncobj_put(syncobjs[i]);
+	}
+
+	kfree(syncobjs);
+}
+
+static int
+virtio_gpu_parse_deps(struct virtio_gpu_submit *submit)
+{
+	struct drm_virtgpu_execbuffer *exbuf = submit->exbuf;
+	struct drm_virtgpu_execbuffer_syncobj syncobj_desc;
+	size_t syncobj_stride = exbuf->syncobj_stride;
+	struct drm_syncobj **syncobjs;
+	int ret = 0, i;
+
+	if (!submit->num_in_syncobjs)
+		return 0;
+
+	syncobjs = kcalloc(submit->num_in_syncobjs, sizeof(*syncobjs),
+			   GFP_KERNEL | __GFP_NOWARN | __GFP_NORETRY);
+	if (!syncobjs)
+		return -ENOMEM;
+
+	for (i = 0; i < submit->num_in_syncobjs; i++) {
+		uint64_t address = exbuf->in_syncobjs + i * syncobj_stride;
+		struct dma_fence *fence;
+
+		if (copy_from_user(&syncobj_desc,
+				   u64_to_user_ptr(address),
+				   min(syncobj_stride, sizeof(syncobj_desc)))) {
+			ret = -EFAULT;
+			break;
+		}
+
+		if (syncobj_desc.flags & ~VIRTGPU_EXECBUF_SYNCOBJ_FLAGS) {
+			ret = -EINVAL;
+			break;
+		}
+
+		ret = drm_syncobj_find_fence(submit->file, syncobj_desc.handle,
+					     syncobj_desc.point, 0, &fence);
+		if (ret)
+			break;
+
+		ret = virtio_gpu_dma_fence_wait(submit, fence);
+
+		dma_fence_put(fence);
+		if (ret)
+			break;
+
+		if (syncobj_desc.flags & VIRTGPU_EXECBUF_SYNCOBJ_RESET) {
+			syncobjs[i] =
+				drm_syncobj_find(submit->file, syncobj_desc.handle);
+			if (!syncobjs[i]) {
+				ret = -EINVAL;
+				break;
+			}
+		}
+	}
+
+	if (ret) {
+		virtio_gpu_free_syncobjs(syncobjs, i);
+		return ret;
+	}
+
+	submit->in_syncobjs = syncobjs;
+
+	return ret;
+}
+
+static void virtio_gpu_reset_syncobjs(struct drm_syncobj **syncobjs,
+				      uint32_t nr_syncobjs)
+{
+	uint32_t i;
+
+	for (i = 0; syncobjs && i < nr_syncobjs; i++) {
+		if (syncobjs[i])
+			drm_syncobj_replace_fence(syncobjs[i], NULL);
+	}
+}
+
+static void
+virtio_gpu_free_post_deps(struct virtio_gpu_submit_post_dep *post_deps,
+			  uint32_t nr_syncobjs)
+{
+	uint32_t i = nr_syncobjs;
+
+	while (post_deps && i--) {
+		kfree(post_deps[i].chain);
+		drm_syncobj_put(post_deps[i].syncobj);
+	}
+
+	kfree(post_deps);
+}
+
+static int virtio_gpu_parse_post_deps(struct virtio_gpu_submit *submit)
+{
+	struct drm_virtgpu_execbuffer *exbuf = submit->exbuf;
+	struct drm_virtgpu_execbuffer_syncobj syncobj_desc;
+	struct virtio_gpu_submit_post_dep *post_deps;
+	size_t syncobj_stride = exbuf->syncobj_stride;
+	int ret = 0, i;
+
+	if (!submit->num_out_syncobjs)
+		return 0;
+
+	post_deps = kcalloc(submit->num_out_syncobjs, sizeof(*post_deps),
+			    GFP_KERNEL | __GFP_NOWARN | __GFP_NORETRY);
+	if (!post_deps)
+		return -ENOMEM;
+
+	for (i = 0; i < submit->num_out_syncobjs; i++) {
+		uint64_t address = exbuf->out_syncobjs + i * syncobj_stride;
+
+		if (copy_from_user(&syncobj_desc,
+				   u64_to_user_ptr(address),
+				   min(syncobj_stride, sizeof(syncobj_desc)))) {
+			ret = -EFAULT;
+			break;
+		}
+
+		post_deps[i].point = syncobj_desc.point;
+
+		if (syncobj_desc.flags) {
+			ret = -EINVAL;
+			break;
+		}
+
+		if (syncobj_desc.point) {
+			post_deps[i].chain = dma_fence_chain_alloc();
+			if (!post_deps[i].chain) {
+				ret = -ENOMEM;
+				break;
+			}
+		}
+
+		post_deps[i].syncobj =
+			drm_syncobj_find(submit->file, syncobj_desc.handle);
+		if (!post_deps[i].syncobj) {
+			ret = -EINVAL;
+			break;
+		}
+	}
+
+	if (ret) {
+		virtio_gpu_free_post_deps(post_deps, i);
+		return ret;
+	}
+
+	submit->post_deps = post_deps;
+
+	return 0;
+}
+
+static void
+virtio_gpu_process_post_deps(struct virtio_gpu_submit *submit)
+{
+	struct virtio_gpu_submit_post_dep *post_deps = submit->post_deps;
+	struct dma_fence *fence = &submit->out_fence->f;
+	uint32_t i;
+
+	for (i = 0; post_deps && i < submit->num_out_syncobjs; i++) {
+		if (post_deps[i].chain) {
+			drm_syncobj_add_point(post_deps[i].syncobj,
+					      post_deps[i].chain,
+					      fence, post_deps[i].point);
+			post_deps[i].chain = NULL;
+		} else {
+			drm_syncobj_replace_fence(post_deps[i].syncobj, fence);
+		}
+	}
+}
+
 static int virtio_gpu_fence_event_create(struct drm_device *dev,
 					 struct drm_file *file,
 					 struct virtio_gpu_fence *fence,
@@ -119,6 +315,11 @@ static int virtio_gpu_init_submit_buflist(struct virtio_gpu_submit *submit)
 
 static void virtio_gpu_cleanup_submit(struct virtio_gpu_submit *submit)
 {
+	virtio_gpu_reset_syncobjs(submit->in_syncobjs, submit->num_in_syncobjs);
+	virtio_gpu_free_syncobjs(submit->in_syncobjs, submit->num_in_syncobjs);
+	virtio_gpu_free_post_deps(submit->post_deps, submit->num_out_syncobjs);
+	kfree(submit->in_fence_ids);
+
 	if (!IS_ERR(submit->buf))
 		kvfree(submit->buf);
 
@@ -164,6 +365,8 @@ static int virtio_gpu_init_submit(struct virtio_gpu_submit *submit,
 		return err;
 	}
 
+	submit->num_out_syncobjs = exbuf->num_out_syncobjs;
+	submit->num_in_syncobjs = exbuf->num_in_syncobjs;
 	submit->out_fence = out_fence;
 	submit->fence_ctx = fence_ctx;
 	submit->ring_idx = ring_idx;
@@ -282,6 +485,14 @@ int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
 	if (ret)
 		goto cleanup;
 
+	ret = virtio_gpu_parse_deps(&submit);
+	if (ret)
+		goto cleanup;
+
+	ret = virtio_gpu_parse_post_deps(&submit);
+	if (ret)
+		goto cleanup;
+
 	ret = virtio_gpu_install_out_fence_fd(&submit);
 	if (ret)
 		goto cleanup;
@@ -291,6 +502,7 @@ int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
 		goto cleanup;
 
 	virtio_gpu_submit(&submit);
+	virtio_gpu_process_post_deps(&submit);
 cleanup:
 	virtio_gpu_cleanup_submit(&submit);
 
diff --git a/include/uapi/drm/virtgpu_drm.h b/include/uapi/drm/virtgpu_drm.h
index 7b158fcb02b4..ce4948aacafd 100644
--- a/include/uapi/drm/virtgpu_drm.h
+++ b/include/uapi/drm/virtgpu_drm.h
@@ -64,6 +64,16 @@ struct drm_virtgpu_map {
 	__u32 pad;
 };
 
+#define VIRTGPU_EXECBUF_SYNCOBJ_RESET		0x01
+#define VIRTGPU_EXECBUF_SYNCOBJ_FLAGS ( \
+		VIRTGPU_EXECBUF_SYNCOBJ_RESET | \
+		0)
+struct drm_virtgpu_execbuffer_syncobj {
+	__u32 handle;
+	__u32 flags;
+	__u64 point;
+};
+
 /* fence_fd is modified on success if VIRTGPU_EXECBUF_FENCE_FD_OUT flag is set. */
 struct drm_virtgpu_execbuffer {
 	__u32 flags;
@@ -73,7 +83,11 @@ struct drm_virtgpu_execbuffer {
 	__u32 num_bo_handles;
 	__s32 fence_fd; /* in/out fence fd (see VIRTGPU_EXECBUF_FENCE_FD_IN/OUT) */
 	__u32 ring_idx; /* command ring index (see VIRTGPU_EXECBUF_RING_IDX) */
-	__u32 pad;
+	__u32 syncobj_stride;
+	__u32 num_in_syncobjs;
+	__u32 num_out_syncobjs;
+	__u64 in_syncobjs;
+	__u64 out_syncobjs;
 };
 
 #define VIRTGPU_PARAM_3D_FEATURES 1 /* do we have 3D features in the hw */
-- 
2.39.2

Re: [PATCH v2 1/2] drm/virtio: Refactor job submission code path

[Rob Clark]

On Sun, Mar 19, 2023 at 9:11 AM Dmitry Osipenko
<dmitry.osipenko@collabora.com> wrote:
>
> Move virtio_gpu_execbuffer_ioctl() into separate virtgpu_submit.c file
> and refactor the code along the way to ease addition of new features to
> the ioctl.
>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> ---
>  drivers/gpu/drm/virtio/Makefile         |   2 +-
>  drivers/gpu/drm/virtio/virtgpu_drv.h    |   4 +
>  drivers/gpu/drm/virtio/virtgpu_ioctl.c  | 182 ---------------
>  drivers/gpu/drm/virtio/virtgpu_submit.c | 298 ++++++++++++++++++++++++
>  4 files changed, 303 insertions(+), 183 deletions(-)
>  create mode 100644 drivers/gpu/drm/virtio/virtgpu_submit.c
>

<snip all the deletes>

> diff --git a/drivers/gpu/drm/virtio/virtgpu_submit.c b/drivers/gpu/drm/virtio/virtgpu_submit.c
> new file mode 100644
> index 000000000000..a96f9d3285c7
> --- /dev/null
> +++ b/drivers/gpu/drm/virtio/virtgpu_submit.c
> @@ -0,0 +1,298 @@
> +// SPDX-License-Identifier: MIT
> +/*
> + * Copyright (C) 2015 Red Hat, Inc.
> + * All Rights Reserved.
> + *
> + * Authors:
> + *    Dave Airlie
> + *    Alon Levy
> + */
> +
> +#include <linux/file.h>
> +#include <linux/sync_file.h>
> +#include <linux/uaccess.h>
> +
> +#include <drm/drm_file.h>
> +#include <drm/virtgpu_drm.h>
> +
> +#include "virtgpu_drv.h"
> +
> +struct virtio_gpu_submit {
> +       struct virtio_gpu_object_array *buflist;
> +       struct drm_virtgpu_execbuffer *exbuf;
> +       struct virtio_gpu_fence *out_fence;
> +       struct virtio_gpu_fpriv *vfpriv;
> +       struct virtio_gpu_device *vgdev;
> +       struct drm_file *file;
> +       uint64_t fence_ctx;
> +       uint32_t ring_idx;
> +       int out_fence_fd;
> +       void *buf;
> +};
> +
> +static int virtio_gpu_do_fence_wait(struct virtio_gpu_submit *submit,
> +                                   struct dma_fence *dma_fence)
> +{
> +       uint32_t context = submit->fence_ctx + submit->ring_idx;
> +
> +       if (dma_fence_match_context(dma_fence, context))
> +               return 0;
> +
> +       return dma_fence_wait(dma_fence, true);
> +}
> +
> +static int virtio_gpu_dma_fence_wait(struct virtio_gpu_submit *submit,
> +                                    struct dma_fence *fence)
> +{
> +       struct dma_fence *itr;
> +       int idx, err;
> +
> +       dma_fence_array_for_each(itr, idx, fence) {

I guess unwrapping is for the later step of host waits?

At any rate, I think you should use dma_fence_unwrap_for_each() to
handle the fence-chain case as well?

> +               err = virtio_gpu_do_fence_wait(submit, itr);
> +               if (err)
> +                       return err;
> +       }
> +
> +       return 0;
> +}
> +
> +static int virtio_gpu_fence_event_create(struct drm_device *dev,
> +                                        struct drm_file *file,
> +                                        struct virtio_gpu_fence *fence,
> +                                        uint32_t ring_idx)
> +{
> +       struct virtio_gpu_fpriv *vfpriv = file->driver_priv;
> +       struct virtio_gpu_fence_event *e = NULL;
> +       int ret;
> +
> +       if (!(vfpriv->ring_idx_mask & BIT_ULL(ring_idx)))
> +               return 0;
> +
> +       e = kzalloc(sizeof(*e), GFP_KERNEL);
> +       if (!e)
> +               return -ENOMEM;
> +
> +       e->event.type = VIRTGPU_EVENT_FENCE_SIGNALED;
> +       e->event.length = sizeof(e->event);
> +
> +       ret = drm_event_reserve_init(dev, file, &e->base, &e->event);
> +       if (ret) {
> +               kfree(e);
> +               return ret;
> +       }
> +
> +       fence->e = e;
> +
> +       return 0;
> +}
> +
> +static int virtio_gpu_init_submit_buflist(struct virtio_gpu_submit *submit)
> +{
> +       struct drm_virtgpu_execbuffer *exbuf = submit->exbuf;
> +       uint32_t *bo_handles;
> +
> +       if (!exbuf->num_bo_handles)
> +               return 0;
> +
> +       bo_handles = kvmalloc_array(exbuf->num_bo_handles, sizeof(uint32_t),
> +                                   GFP_KERNEL);
> +       if (!bo_handles)
> +               return -ENOMEM;
> +
> +       if (copy_from_user(bo_handles, u64_to_user_ptr(exbuf->bo_handles),
> +                          exbuf->num_bo_handles * sizeof(uint32_t))) {
> +               kvfree(bo_handles);
> +               return -EFAULT;
> +       }
> +
> +       submit->buflist = virtio_gpu_array_from_handles(submit->file, bo_handles,
> +                                                       exbuf->num_bo_handles);
> +       if (!submit->buflist) {
> +               kvfree(bo_handles);
> +               return -ENOENT;
> +       }
> +
> +       kvfree(bo_handles);
> +
> +       return 0;
> +}
> +
> +static void virtio_gpu_cleanup_submit(struct virtio_gpu_submit *submit)
> +{
> +       if (!IS_ERR(submit->buf))
> +               kvfree(submit->buf);
> +
> +       if (submit->buflist)
> +               virtio_gpu_array_put_free(submit->buflist);
> +
> +       if (submit->out_fence_fd >= 0)
> +               put_unused_fd(submit->out_fence_fd);
> +}
> +
> +static void virtio_gpu_submit(struct virtio_gpu_submit *submit)
> +{
> +       virtio_gpu_cmd_submit(submit->vgdev, submit->buf, submit->exbuf->size,
> +                             submit->vfpriv->ctx_id, submit->buflist,
> +                             submit->out_fence);
> +       virtio_gpu_notify(submit->vgdev);
> +
> +       submit->buf = NULL;
> +       submit->buflist = NULL;
> +       submit->out_fence_fd = -1;
> +}
> +
> +static int virtio_gpu_init_submit(struct virtio_gpu_submit *submit,
> +                                 struct drm_virtgpu_execbuffer *exbuf,
> +                                 struct drm_device *dev,
> +                                 struct drm_file *file,
> +                                 uint64_t fence_ctx, uint32_t ring_idx)
> +{
> +       struct virtio_gpu_fpriv *vfpriv = file->driver_priv;
> +       struct virtio_gpu_device *vgdev = dev->dev_private;
> +       struct virtio_gpu_fence *out_fence;
> +       int err;
> +
> +       memset(submit, 0, sizeof(*submit));
> +
> +       out_fence = virtio_gpu_fence_alloc(vgdev, fence_ctx, ring_idx);
> +       if (!out_fence)
> +               return -ENOMEM;
> +
> +       err = virtio_gpu_fence_event_create(dev, file, out_fence, ring_idx);
> +       if (err) {
> +               dma_fence_put(&out_fence->f);
> +               return err;
> +       }

If we fail at any point after here, where is the out_fence referenced dropped?

> +
> +       submit->out_fence = out_fence;
> +       submit->fence_ctx = fence_ctx;
> +       submit->ring_idx = ring_idx;
> +       submit->out_fence_fd = -1;
> +       submit->vfpriv = vfpriv;
> +       submit->vgdev = vgdev;
> +       submit->exbuf = exbuf;
> +       submit->file = file;
> +
> +       err = virtio_gpu_init_submit_buflist(submit);
> +       if (err)
> +               return err;
> +
> +       submit->buf = vmemdup_user(u64_to_user_ptr(exbuf->command), exbuf->size);
> +       if (IS_ERR(submit->buf))
> +               return PTR_ERR(submit->buf);
> +
> +       if (exbuf->flags & VIRTGPU_EXECBUF_FENCE_FD_OUT) {
> +               err = get_unused_fd_flags(O_CLOEXEC);
> +               if (err < 0)
> +                       return err;
> +
> +               submit->out_fence_fd = err;
> +       }
> +
> +       return 0;
> +}
> +
> +static int virtio_gpu_wait_in_fence(struct virtio_gpu_submit *submit)
> +{
> +       int ret = 0;
> +
> +       if (submit->exbuf->flags & VIRTGPU_EXECBUF_FENCE_FD_IN) {
> +               struct dma_fence *in_fence =
> +                               sync_file_get_fence(submit->exbuf->fence_fd);
> +               if (!in_fence)
> +                       return -EINVAL;
> +
> +               /*
> +                * Wait if the fence is from a foreign context, or if the fence
> +                * array contains any fence from a foreign context.
> +                */
> +               ret = virtio_gpu_dma_fence_wait(submit, in_fence);
> +
> +               dma_fence_put(in_fence);
> +       }
> +
> +       return ret;
> +}
> +
> +static int virtio_gpu_install_out_fence_fd(struct virtio_gpu_submit *submit)
> +{
> +       if (submit->out_fence_fd >= 0) {
> +               struct sync_file *sync_file =
> +                                       sync_file_create(&submit->out_fence->f);
> +               if (!sync_file)
> +                       return -ENOMEM;
> +
> +               submit->exbuf->fence_fd = submit->out_fence_fd;
> +               fd_install(submit->out_fence_fd, sync_file->file);
> +       }
> +
> +       return 0;
> +}
> +
> +static int virtio_gpu_lock_buflist(struct virtio_gpu_submit *submit)
> +{
> +       if (submit->buflist)
> +               return virtio_gpu_array_lock_resv(submit->buflist);
> +
> +       return 0;
> +}
> +
> +/*
> + * Usage of execbuffer:
> + * Relocations need to take into account the full VIRTIO_GPUDrawable size.
> + * However, the command as passed from user space must *not* contain the initial
> + * VIRTIO_GPUReleaseInfo struct (first XXX bytes)
> + */

I know this is just getting moved from the old location, but I'm not
even sure what this comment means ;-)

At least it doesn't make any sense for non-virgl contexts.. I haven't
looked too closely at virgl protocol itself

BR,
-R

> +int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
> +                               struct drm_file *file)
> +{
> +       struct virtio_gpu_device *vgdev = dev->dev_private;
> +       struct virtio_gpu_fpriv *vfpriv = file->driver_priv;
> +       uint64_t fence_ctx = vgdev->fence_drv.context;
> +       struct drm_virtgpu_execbuffer *exbuf = data;
> +       struct virtio_gpu_submit submit;
> +       uint32_t ring_idx = 0;
> +       int ret = -EINVAL;
> +
> +       if (vgdev->has_virgl_3d == false)
> +               return -ENOSYS;
> +
> +       if ((exbuf->flags & ~VIRTGPU_EXECBUF_FLAGS))
> +               return ret;
> +
> +       if ((exbuf->flags & VIRTGPU_EXECBUF_RING_IDX)) {
> +               if (exbuf->ring_idx >= vfpriv->num_rings)
> +                       return ret;
> +
> +               if (!vfpriv->base_fence_ctx)
> +                       return ret;
> +
> +               fence_ctx = vfpriv->base_fence_ctx;
> +               ring_idx = exbuf->ring_idx;
> +       }
> +
> +       virtio_gpu_create_context(dev, file);
> +
> +       ret = virtio_gpu_init_submit(&submit, exbuf, dev, file,
> +                                    fence_ctx, ring_idx);
> +       if (ret)
> +               goto cleanup;
> +
> +       ret = virtio_gpu_wait_in_fence(&submit);
> +       if (ret)
> +               goto cleanup;
> +
> +       ret = virtio_gpu_install_out_fence_fd(&submit);
> +       if (ret)
> +               goto cleanup;
> +
> +       ret = virtio_gpu_lock_buflist(&submit);
> +       if (ret)
> +               goto cleanup;
> +
> +       virtio_gpu_submit(&submit);
> +cleanup:
> +       virtio_gpu_cleanup_submit(&submit);
> +
> +       return ret;
> +}
> --
> 2.39.2
>

Re: [PATCH v2 1/2] drm/virtio: Refactor job submission code path

[Dmitry Osipenko]

On 3/23/23 00:25, Rob Clark wrote:
...
>> +static int virtio_gpu_dma_fence_wait(struct virtio_gpu_submit *submit,
>> +                                    struct dma_fence *fence)
>> +{
>> +       struct dma_fence *itr;
>> +       int idx, err;
>> +
>> +       dma_fence_array_for_each(itr, idx, fence) {
> 
> I guess unwrapping is for the later step of host waits?
> 
> At any rate, I think you should use dma_fence_unwrap_for_each() to
> handle the fence-chain case as well?

Yes, seems so. I actually missed the dma_fence_unwrap, thanks!

...
>> +static int virtio_gpu_init_submit(struct virtio_gpu_submit *submit,
>> +                                 struct drm_virtgpu_execbuffer *exbuf,
>> +                                 struct drm_device *dev,
>> +                                 struct drm_file *file,
>> +                                 uint64_t fence_ctx, uint32_t ring_idx)
>> +{
>> +       struct virtio_gpu_fpriv *vfpriv = file->driver_priv;
>> +       struct virtio_gpu_device *vgdev = dev->dev_private;
>> +       struct virtio_gpu_fence *out_fence;
>> +       int err;
>> +
>> +       memset(submit, 0, sizeof(*submit));
>> +
>> +       out_fence = virtio_gpu_fence_alloc(vgdev, fence_ctx, ring_idx);
>> +       if (!out_fence)
>> +               return -ENOMEM;
>> +
>> +       err = virtio_gpu_fence_event_create(dev, file, out_fence, ring_idx);
>> +       if (err) {
>> +               dma_fence_put(&out_fence->f);
>> +               return err;
>> +       }
> 
> If we fail at any point after here, where is the out_fence referenced dropped?

Good catch, don't see either where it's dropped. Perhaps the drop got
lost after moving the code around, will fix.

...
>> +/*
>> + * Usage of execbuffer:
>> + * Relocations need to take into account the full VIRTIO_GPUDrawable size.
>> + * However, the command as passed from user space must *not* contain the initial
>> + * VIRTIO_GPUReleaseInfo struct (first XXX bytes)
>> + */
> 
> I know this is just getting moved from the old location, but I'm not
> even sure what this comment means ;-)
> 
> At least it doesn't make any sense for non-virgl contexts.. I haven't
> looked too closely at virgl protocol itself

Had exactly the same thought :) Well, if nobody will clarify, then I'm
happy with removing it in v3.

-- 
Best regards,
Dmitry