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, 279 insertions, 8 deletions

diff --git a/drivers/gpu/drm/vc4/vc4_bo.c b/drivers/gpu/drm/vc4/vc4_bo.c
index 3afdbf4bc10b..01a53ba304f8 100644
--- a/drivers/gpu/drm/vc4/vc4_bo.c
+++ b/drivers/gpu/drm/vc4/vc4_bo.c
@@ -53,6 +53,17 @@ static void vc4_bo_stats_dump(struct vc4_dev *vc4)
 			 vc4->bo_labels[i].size_allocated / 1024,
 			 vc4->bo_labels[i].num_allocated);
 	}
+
+	mutex_lock(&vc4->purgeable.lock);
+	if (vc4->purgeable.num)
+		DRM_INFO("%30s: %6zdkb BOs (%d)\n", "userspace BO cache",
+			 vc4->purgeable.size / 1024, vc4->purgeable.num);
+
+	if (vc4->purgeable.purged_num)
+		DRM_INFO("%30s: %6zdkb BOs (%d)\n", "total purged BO",
+			 vc4->purgeable.purged_size / 1024,
+			 vc4->purgeable.purged_num);
+	mutex_unlock(&vc4->purgeable.lock);
 }
 
 #ifdef CONFIG_DEBUG_FS
@@ -75,6 +86,17 @@ int vc4_bo_stats_debugfs(struct seq_file *m, void *unused)
 	}
 	mutex_unlock(&vc4->bo_lock);
 
+	mutex_lock(&vc4->purgeable.lock);
+	if (vc4->purgeable.num)
+		seq_printf(m, "%30s: %6dkb BOs (%d)\n", "userspace BO cache",
+			   vc4->purgeable.size / 1024, vc4->purgeable.num);
+
+	if (vc4->purgeable.purged_num)
+		seq_printf(m, "%30s: %6dkb BOs (%d)\n", "total purged BO",
+			   vc4->purgeable.purged_size / 1024,
+			   vc4->purgeable.purged_num);
+	mutex_unlock(&vc4->purgeable.lock);
+
 	return 0;
 }
 #endif
@@ -247,6 +269,109 @@ static void vc4_bo_cache_purge(struct drm_device *dev)
 	mutex_unlock(&vc4->bo_lock);
 }
 
+void vc4_bo_add_to_purgeable_pool(struct vc4_bo *bo)
+{
+	struct vc4_dev *vc4 = to_vc4_dev(bo->base.base.dev);
+
+	mutex_lock(&vc4->purgeable.lock);
+	list_add_tail(&bo->size_head, &vc4->purgeable.list);
+	vc4->purgeable.num++;
+	vc4->purgeable.size += bo->base.base.size;
+	mutex_unlock(&vc4->purgeable.lock);
+}
+
+static void vc4_bo_remove_from_purgeable_pool_locked(struct vc4_bo *bo)
+{
+	struct vc4_dev *vc4 = to_vc4_dev(bo->base.base.dev);
+
+	/* list_del_init() is used here because the caller might release
+	 * the purgeable lock in order to acquire the madv one and update the
+	 * madv status.
+	 * During this short period of time a user might decide to mark
+	 * the BO as unpurgeable, and if bo->madv is set to
+	 * VC4_MADV_DONTNEED it will try to remove the BO from the
+	 * purgeable list which will fail if the ->next/prev fields
+	 * are set to LIST_POISON1/LIST_POISON2 (which is what
+	 * list_del() does).
+	 * Re-initializing the list element guarantees that list_del()
+	 * will work correctly even if it's a NOP.
+	 */
+	list_del_init(&bo->size_head);
+	vc4->purgeable.num--;
+	vc4->purgeable.size -= bo->base.base.size;
+}
+
+void vc4_bo_remove_from_purgeable_pool(struct vc4_bo *bo)
+{
+	struct vc4_dev *vc4 = to_vc4_dev(bo->base.base.dev);
+
+	mutex_lock(&vc4->purgeable.lock);
+	vc4_bo_remove_from_purgeable_pool_locked(bo);
+	mutex_unlock(&vc4->purgeable.lock);
+}
+
+static void vc4_bo_purge(struct drm_gem_object *obj)
+{
+	struct vc4_bo *bo = to_vc4_bo(obj);
+	struct drm_device *dev = obj->dev;
+
+	WARN_ON(!mutex_is_locked(&bo->madv_lock));
+	WARN_ON(bo->madv != VC4_MADV_DONTNEED);
+
+	drm_vma_node_unmap(&obj->vma_node, dev->anon_inode->i_mapping);
+
+	dma_free_wc(dev->dev, obj->size, bo->base.vaddr, bo->base.paddr);
+	bo->base.vaddr = NULL;
+	bo->madv = __VC4_MADV_PURGED;
+}
+
+static void vc4_bo_userspace_cache_purge(struct drm_device *dev)
+{
+	struct vc4_dev *vc4 = to_vc4_dev(dev);
+
+	mutex_lock(&vc4->purgeable.lock);
+	while (!list_empty(&vc4->purgeable.list)) {
+		struct vc4_bo *bo = list_first_entry(&vc4->purgeable.list,
+						     struct vc4_bo, size_head);
+		struct drm_gem_object *obj = &bo->base.base;
+		size_t purged_size = 0;
+
+		vc4_bo_remove_from_purgeable_pool_locked(bo);
+
+		/* Release the purgeable lock while we're purging the BO so
+		 * that other people can continue inserting things in the
+		 * purgeable pool without having to wait for all BOs to be
+		 * purged.
+		 */
+		mutex_unlock(&vc4->purgeable.lock);
+		mutex_lock(&bo->madv_lock);
+
+		/* Since we released the purgeable pool lock before acquiring
+		 * the BO madv one, the user may have marked the BO as WILLNEED
+		 * and re-used it in the meantime.
+		 * Before purging the BO we need to make sure
+		 * - it is still marked as DONTNEED
+		 * - it has not been re-inserted in the purgeable list
+		 * - it is not used by HW blocks
+		 * If one of these conditions is not met, just skip the entry.
+		 */
+		if (bo->madv == VC4_MADV_DONTNEED &&
+		    list_empty(&bo->size_head) &&
+		    !refcount_read(&bo->usecnt)) {
+			purged_size = bo->base.base.size;
+			vc4_bo_purge(obj);
+		}
+		mutex_unlock(&bo->madv_lock);
+		mutex_lock(&vc4->purgeable.lock);
+
+		if (purged_size) {
+			vc4->purgeable.purged_size += purged_size;
+			vc4->purgeable.purged_num++;
+		}
+	}
+	mutex_unlock(&vc4->purgeable.lock);
+}
+
 static struct vc4_bo *vc4_bo_get_from_cache(struct drm_device *dev,
 					    uint32_t size,
 					    enum vc4_kernel_bo_type type)
@@ -293,6 +418,9 @@ struct drm_gem_object *vc4_create_object(struct drm_device *dev, size_t size)
 	if (!bo)
 		return ERR_PTR(-ENOMEM);
 
+	bo->madv = VC4_MADV_WILLNEED;
+	refcount_set(&bo->usecnt, 0);
+	mutex_init(&bo->madv_lock);
 	mutex_lock(&vc4->bo_lock);
 	bo->label = VC4_BO_TYPE_KERNEL;
 	vc4->bo_labels[VC4_BO_TYPE_KERNEL].num_allocated++;
@@ -330,16 +458,38 @@ struct vc4_bo *vc4_bo_create(struct drm_device *dev, size_t unaligned_size,
 		 * CMA allocations we've got laying around and try again.
 		 */
 		vc4_bo_cache_purge(dev);
+		cma_obj = drm_gem_cma_create(dev, size);
+	}
 
+	if (IS_ERR(cma_obj)) {
+		/*
+		 * Still not enough CMA memory, purge the userspace BO
+		 * cache and retry.
+		 * This is sub-optimal since we purge the whole userspace
+		 * BO cache which forces user that want to re-use the BO to
+		 * restore its initial content.
+		 * Ideally, we should purge entries one by one and retry
+		 * after each to see if CMA allocation succeeds. Or even
+		 * better, try to find an entry with at least the same
+		 * size.
+		 */
+		vc4_bo_userspace_cache_purge(dev);
 		cma_obj = drm_gem_cma_create(dev, size);
-		if (IS_ERR(cma_obj)) {
-			DRM_ERROR("Failed to allocate from CMA:\n");
-			vc4_bo_stats_dump(vc4);
-			return ERR_PTR(-ENOMEM);
-		}
+	}
+
+	if (IS_ERR(cma_obj)) {
+		DRM_ERROR("Failed to allocate from CMA:\n");
+		vc4_bo_stats_dump(vc4);
+		return ERR_PTR(-ENOMEM);
 	}
 	bo = to_vc4_bo(&cma_obj->base);
 
+	/* By default, BOs do not support the MADV ioctl. This will be enabled
+	 * only on BOs that are exposed to userspace (V3D, V3D_SHADER and DUMB
+	 * BOs).
+	 */
+	bo->madv = __VC4_MADV_NOTSUPP;
+
 	mutex_lock(&vc4->bo_lock);
 	vc4_bo_set_label(&cma_obj->base, type);
 	mutex_unlock(&vc4->bo_lock);
@@ -365,6 +515,8 @@ int vc4_dumb_create(struct drm_file *file_priv,
 	if (IS_ERR(bo))
 		return PTR_ERR(bo);
 
+	bo->madv = VC4_MADV_WILLNEED;
+
 	ret = drm_gem_handle_create(file_priv, &bo->base.base, &args->handle);
 	drm_gem_object_put_unlocked(&bo->base.base);
 
@@ -403,6 +555,12 @@ void vc4_free_object(struct drm_gem_object *gem_bo)
 	struct vc4_bo *bo = to_vc4_bo(gem_bo);
 	struct list_head *cache_list;
 
+	/* Remove the BO from the purgeable list. */
+	mutex_lock(&bo->madv_lock);
+	if (bo->madv == VC4_MADV_DONTNEED && !refcount_read(&bo->usecnt))
+		vc4_bo_remove_from_purgeable_pool(bo);
+	mutex_unlock(&bo->madv_lock);
+
 	mutex_lock(&vc4->bo_lock);
 	/* If the object references someone else's memory, we can't cache it.
 	 */
@@ -418,7 +576,8 @@ void vc4_free_object(struct drm_gem_object *gem_bo)
 	}
 
 	/* If this object was partially constructed but CMA allocation
-	 * had failed, just free it.
+	 * had failed, just free it. Can also happen when the BO has been
+	 * purged.
 	 */
 	if (!bo->base.vaddr) {
 		vc4_bo_destroy(bo);
@@ -437,6 +596,10 @@ void vc4_free_object(struct drm_gem_object *gem_bo)
 		bo->validated_shader = NULL;
 	}
 
+	/* Reset madv and usecnt before adding the BO to the cache. */
+	bo->madv = __VC4_MADV_NOTSUPP;
+	refcount_set(&bo->usecnt, 0);
+
 	bo->t_format = false;
 	bo->free_time = jiffies;
 	list_add(&bo->size_head, cache_list);
@@ -461,6 +624,56 @@ static void vc4_bo_cache_time_work(struct work_struct *work)
 	mutex_unlock(&vc4->bo_lock);
 }
 
+int vc4_bo_inc_usecnt(struct vc4_bo *bo)
+{
+	int ret;
+
+	/* Fast path: if the BO is already retained by someone, no need to
+	 * check the madv status.
+	 */
+	if (refcount_inc_not_zero(&bo->usecnt))
+		return 0;
+
+	mutex_lock(&bo->madv_lock);
+	switch (bo->madv) {
+	case VC4_MADV_WILLNEED:
+		refcount_inc(&bo->usecnt);
+		ret = 0;
+		break;
+	case VC4_MADV_DONTNEED:
+		/* We shouldn't use a BO marked as purgeable if at least
+		 * someone else retained its content by incrementing usecnt.
+		 * Luckily the BO hasn't been purged yet, but something wrong
+		 * is happening here. Just throw an error instead of
+		 * authorizing this use case.
+		 */
+	case __VC4_MADV_PURGED:
+		/* We can't use a purged BO. */
+	default:
+		/* Invalid madv value. */
+		ret = -EINVAL;
+		break;
+	}
+	mutex_unlock(&bo->madv_lock);
+
+	return ret;
+}
+
+void vc4_bo_dec_usecnt(struct vc4_bo *bo)
+{
+	/* Fast path: if the BO is still retained by someone, no need to test
+	 * the madv value.
+	 */
+	if (refcount_dec_not_one(&bo->usecnt))
+		return;
+
+	mutex_lock(&bo->madv_lock);
+	if (refcount_dec_and_test(&bo->usecnt) &&
+	    bo->madv == VC4_MADV_DONTNEED)
+		vc4_bo_add_to_purgeable_pool(bo);
+	mutex_unlock(&bo->madv_lock);
+}
+
 static void vc4_bo_cache_time_timer(unsigned long data)
 {
 	struct drm_device *dev = (struct drm_device *)data;
@@ -480,18 +693,52 @@ struct dma_buf *
 vc4_prime_export(struct drm_device *dev, struct drm_gem_object *obj, int flags)
 {
 	struct vc4_bo *bo = to_vc4_bo(obj);
+	struct dma_buf *dmabuf;
+	int ret;
 
 	if (bo->validated_shader) {
 		DRM_DEBUG("Attempting to export shader BO\n");
 		return ERR_PTR(-EINVAL);
 	}
 
-	return drm_gem_prime_export(dev, obj, flags);
+	/* Note: as soon as the BO is exported it becomes unpurgeable, because
+	 * noone ever decrements the usecnt even if the reference held by the
+	 * exported BO is released. This shouldn't be a problem since we don't
+	 * expect exported BOs to be marked as purgeable.
+	 */
+	ret = vc4_bo_inc_usecnt(bo);
+	if (ret) {
+		DRM_ERROR("Failed to increment BO usecnt\n");
+		return ERR_PTR(ret);
+	}
+
+	dmabuf = drm_gem_prime_export(dev, obj, flags);
+	if (IS_ERR(dmabuf))
+		vc4_bo_dec_usecnt(bo);
+
+	return dmabuf;
+}
+
+int vc4_fault(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct drm_gem_object *obj = vma->vm_private_data;
+	struct vc4_bo *bo = to_vc4_bo(obj);
+
+	/* The only reason we would end up here is when user-space accesses
+	 * BO's memory after it's been purged.
+	 */
+	mutex_lock(&bo->madv_lock);
+	WARN_ON(bo->madv != __VC4_MADV_PURGED);
+	mutex_unlock(&bo->madv_lock);
+
+	return VM_FAULT_SIGBUS;
 }
 
 int vc4_mmap(struct file *filp, struct vm_area_struct *vma)
 {
 	struct drm_gem_object *gem_obj;
+	unsigned long vm_pgoff;
 	struct vc4_bo *bo;
 	int ret;
 
@@ -507,16 +754,36 @@ int vc4_mmap(struct file *filp, struct vm_area_struct *vma)
 		return -EINVAL;
 	}
 
+	if (bo->madv != VC4_MADV_WILLNEED) {
+		DRM_DEBUG("mmaping of %s BO not allowed\n",
+			  bo->madv == VC4_MADV_DONTNEED ?
+			  "purgeable" : "purged");
+		return -EINVAL;
+	}
+
 	/*
 	 * Clear the VM_PFNMAP flag that was set by drm_gem_mmap(), and set the
 	 * vm_pgoff (used as a fake buffer offset by DRM) to 0 as we want to map
 	 * the whole buffer.
 	 */
 	vma->vm_flags &= ~VM_PFNMAP;
-	vma->vm_pgoff = 0;
 
+	/* This ->vm_pgoff dance is needed to make all parties happy:
+	 * - dma_mmap_wc() uses ->vm_pgoff as an offset within the allocated
+	 *   mem-region, hence the need to set it to zero (the value set by
+	 *   the DRM core is a virtual offset encoding the GEM object-id)
+	 * - the mmap() core logic needs ->vm_pgoff to be restored to its
+	 *   initial value before returning from this function because it
+	 *   encodes the  offset of this GEM in the dev->anon_inode pseudo-file
+	 *   and this information will be used when we invalidate userspace
+	 *   mappings  with drm_vma_node_unmap() (called from vc4_gem_purge()).
+	 */
+	vm_pgoff = vma->vm_pgoff;
+	vma->vm_pgoff = 0;
 	ret = dma_mmap_wc(bo->base.base.dev->dev, vma, bo->base.vaddr,
 			  bo->base.paddr, vma->vm_end - vma->vm_start);
+	vma->vm_pgoff = vm_pgoff;
+
 	if (ret)
 		drm_gem_vm_close(vma);
 
@@ -580,6 +847,8 @@ int vc4_create_bo_ioctl(struct drm_device *dev, void *data,
 	if (IS_ERR(bo))
 		return PTR_ERR(bo);
 
+	bo->madv = VC4_MADV_WILLNEED;
+
 	ret = drm_gem_handle_create(file_priv, &bo->base.base, &args->handle);
 	drm_gem_object_put_unlocked(&bo->base.base);
 
@@ -633,6 +902,8 @@ vc4_create_shader_bo_ioctl(struct drm_device *dev, void *data,
 	if (IS_ERR(bo))
 		return PTR_ERR(bo);
 
+	bo->madv = VC4_MADV_WILLNEED;
+
 	if (copy_from_user(bo->base.vaddr,
 			     (void __user *)(uintptr_t)args->data,
 			     args->size)) {