drm/vc4: Add the DRM_IOCTL_VC4_GEM_MADVISE ioctl

This ioctl will allow us to purge inactive userspace buffers when the
system is running out of contiguous memory.

For now, the purge logic is rather dumb in that it does not try to
release only the amount of BO needed to meet the last CMA alloc request
but instead purges all objects placed in the purgeable pool as soon as
we experience a CMA allocation failure.

Note that the in-kernel BO cache is always purged before the purgeable
cache because those objects are known to be unused while objects marked
as purgeable by a userspace application/library might have to be
restored when they are marked back as unpurgeable, which can be
expensive.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20171019125748.3152-1-boris.brezillon@free-electrons.com

1 files changed, 150 insertions, 6 deletions

diff --git a/drivers/gpu/drm/vc4/vc4_gem.c b/drivers/gpu/drm/vc4/vc4_gem.c
index d0c6bfb68c4e..e00ac2f3a264 100644
--- a/drivers/gpu/drm/vc4/vc4_gem.c
+++ b/drivers/gpu/drm/vc4/vc4_gem.c
@@ -188,11 +188,22 @@ vc4_save_hang_state(struct drm_device *dev)
 			continue;
 
 		for (j = 0; j < exec[i]->bo_count; j++) {
+			bo = to_vc4_bo(&exec[i]->bo[j]->base);
+
+			/* Retain BOs just in case they were marked purgeable.
+			 * This prevents the BO from being purged before
+			 * someone had a chance to dump the hang state.
+			 */
+			WARN_ON(!refcount_read(&bo->usecnt));
+			refcount_inc(&bo->usecnt);
 			drm_gem_object_get(&exec[i]->bo[j]->base);
 			kernel_state->bo[j + prev_idx] = &exec[i]->bo[j]->base;
 		}
 
 		list_for_each_entry(bo, &exec[i]->unref_list, unref_head) {
+			/* No need to retain BOs coming from the ->unref_list
+			 * because they are naturally unpurgeable.
+			 */
 			drm_gem_object_get(&bo->base.base);
 			kernel_state->bo[j + prev_idx] = &bo->base.base;
 			j++;
@@ -233,6 +244,26 @@ vc4_save_hang_state(struct drm_device *dev)
 	state->fdbgs = V3D_READ(V3D_FDBGS);
 	state->errstat = V3D_READ(V3D_ERRSTAT);
 
+	/* We need to turn purgeable BOs into unpurgeable ones so that
+	 * userspace has a chance to dump the hang state before the kernel
+	 * decides to purge those BOs.
+	 * Note that BO consistency at dump time cannot be guaranteed. For
+	 * example, if the owner of these BOs decides to re-use them or mark
+	 * them purgeable again there's nothing we can do to prevent it.
+	 */
+	for (i = 0; i < kernel_state->user_state.bo_count; i++) {
+		struct vc4_bo *bo = to_vc4_bo(kernel_state->bo[i]);
+
+		if (bo->madv == __VC4_MADV_NOTSUPP)
+			continue;
+
+		mutex_lock(&bo->madv_lock);
+		if (!WARN_ON(bo->madv == __VC4_MADV_PURGED))
+			bo->madv = VC4_MADV_WILLNEED;
+		refcount_dec(&bo->usecnt);
+		mutex_unlock(&bo->madv_lock);
+	}
+
 	spin_lock_irqsave(&vc4->job_lock, irqflags);
 	if (vc4->hang_state) {
 		spin_unlock_irqrestore(&vc4->job_lock, irqflags);
@@ -639,9 +670,6 @@ vc4_queue_submit(struct drm_device *dev, struct vc4_exec_info *exec,
  * The command validator needs to reference BOs by their index within
  * the submitted job's BO list.  This does the validation of the job's
  * BO list and reference counting for the lifetime of the job.
- *
- * Note that this function doesn't need to unreference the BOs on
- * failure, because that will happen at vc4_complete_exec() time.
  */
 static int
 vc4_cl_lookup_bos(struct drm_device *dev,
@@ -693,16 +721,47 @@ vc4_cl_lookup_bos(struct drm_device *dev,
 			DRM_DEBUG("Failed to look up GEM BO %d: %d\n",
 				  i, handles[i]);
 			ret = -EINVAL;
-			spin_unlock(&file_priv->table_lock);
-			goto fail;
+			break;
 		}
+
 		drm_gem_object_get(bo);
 		exec->bo[i] = (struct drm_gem_cma_object *)bo;
 	}
 	spin_unlock(&file_priv->table_lock);
 
+	if (ret)
+		goto fail_put_bo;
+
+	for (i = 0; i < exec->bo_count; i++) {
+		ret = vc4_bo_inc_usecnt(to_vc4_bo(&exec->bo[i]->base));
+		if (ret)
+			goto fail_dec_usecnt;
+	}
+
+	kvfree(handles);
+	return 0;
+
+fail_dec_usecnt:
+	/* Decrease usecnt on acquired objects.
+	 * We cannot rely on  vc4_complete_exec() to release resources here,
+	 * because vc4_complete_exec() has no information about which BO has
+	 * had its ->usecnt incremented.
+	 * To make things easier we just free everything explicitly and set
+	 * exec->bo to NULL so that vc4_complete_exec() skips the 'BO release'
+	 * step.
+	 */
+	for (i-- ; i >= 0; i--)
+		vc4_bo_dec_usecnt(to_vc4_bo(&exec->bo[i]->base));
+
+fail_put_bo:
+	/* Release any reference to acquired objects. */
+	for (i = 0; i < exec->bo_count && exec->bo[i]; i++)
+		drm_gem_object_put_unlocked(&exec->bo[i]->base);
+
 fail:
 	kvfree(handles);
+	kvfree(exec->bo);
+	exec->bo = NULL;
 	return ret;
 }
 
@@ -833,8 +892,12 @@ vc4_complete_exec(struct drm_device *dev, struct vc4_exec_info *exec)
 		dma_fence_signal(exec->fence);
 
 	if (exec->bo) {
-		for (i = 0; i < exec->bo_count; i++)
+		for (i = 0; i < exec->bo_count; i++) {
+			struct vc4_bo *bo = to_vc4_bo(&exec->bo[i]->base);
+
+			vc4_bo_dec_usecnt(bo);
 			drm_gem_object_put_unlocked(&exec->bo[i]->base);
+		}
 		kvfree(exec->bo);
 	}
 
@@ -1098,6 +1161,9 @@ vc4_gem_init(struct drm_device *dev)
 	INIT_WORK(&vc4->job_done_work, vc4_job_done_work);
 
 	mutex_init(&vc4->power_lock);
+
+	INIT_LIST_HEAD(&vc4->purgeable.list);
+	mutex_init(&vc4->purgeable.lock);
 }
 
 void
@@ -1121,3 +1187,81 @@ vc4_gem_destroy(struct drm_device *dev)
 	if (vc4->hang_state)
 		vc4_free_hang_state(dev, vc4->hang_state);
 }
+
+int vc4_gem_madvise_ioctl(struct drm_device *dev, void *data,
+			  struct drm_file *file_priv)
+{
+	struct drm_vc4_gem_madvise *args = data;
+	struct drm_gem_object *gem_obj;
+	struct vc4_bo *bo;
+	int ret;
+
+	switch (args->madv) {
+	case VC4_MADV_DONTNEED:
+	case VC4_MADV_WILLNEED:
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	if (args->pad != 0)
+		return -EINVAL;
+
+	gem_obj = drm_gem_object_lookup(file_priv, args->handle);
+	if (!gem_obj) {
+		DRM_DEBUG("Failed to look up GEM BO %d\n", args->handle);
+		return -ENOENT;
+	}
+
+	bo = to_vc4_bo(gem_obj);
+
+	/* Only BOs exposed to userspace can be purged. */
+	if (bo->madv == __VC4_MADV_NOTSUPP) {
+		DRM_DEBUG("madvise not supported on this BO\n");
+		ret = -EINVAL;
+		goto out_put_gem;
+	}
+
+	/* Not sure it's safe to purge imported BOs. Let's just assume it's
+	 * not until proven otherwise.
+	 */
+	if (gem_obj->import_attach) {
+		DRM_DEBUG("madvise not supported on imported BOs\n");
+		ret = -EINVAL;
+		goto out_put_gem;
+	}
+
+	mutex_lock(&bo->madv_lock);
+
+	if (args->madv == VC4_MADV_DONTNEED && bo->madv == VC4_MADV_WILLNEED &&
+	    !refcount_read(&bo->usecnt)) {
+		/* If the BO is about to be marked as purgeable, is not used
+		 * and is not already purgeable or purged, add it to the
+		 * purgeable list.
+		 */
+		vc4_bo_add_to_purgeable_pool(bo);
+	} else if (args->madv == VC4_MADV_WILLNEED &&
+		   bo->madv == VC4_MADV_DONTNEED &&
+		   !refcount_read(&bo->usecnt)) {
+		/* The BO has not been purged yet, just remove it from
+		 * the purgeable list.
+		 */
+		vc4_bo_remove_from_purgeable_pool(bo);
+	}
+
+	/* Save the purged state. */
+	args->retained = bo->madv != __VC4_MADV_PURGED;
+
+	/* Update internal madv state only if the bo was not purged. */
+	if (bo->madv != __VC4_MADV_PURGED)
+		bo->madv = args->madv;
+
+	mutex_unlock(&bo->madv_lock);
+
+	ret = 0;
+
+out_put_gem:
+	drm_gem_object_put_unlocked(gem_obj);
+
+	return ret;
+}