[PATCH 0/2] Fix leaking of cached Host1x buffer objects

[PATCH 0/2] Fix leaking of cached Host1x buffer objects

[Mikko Perttunen]

Host1x implements a mechanism to cache buffer object mappings to allow 
skipping costly map/unmap cycles for buffers that where that commonly 
happens (buffers used with display). The intention was that once the 
user frees the buffer, the cache mapping also goes away.

However, the cached mapping was also keeping a refcount on the buffer, 
so the code freeing the buffer -- and releasing the cached mapping -- 
would never run, hence leaking any buffer used with the cache.

Fix by making cache's reference to the buffer weak.

Merging notes:

The change to the crypto driver is safe to merge independently. The 
driver keeps its own refcount regardless so the buffer won't get freed 
incorrectly.

---
Mikko Perttunen (2):
      gpu: host1x: Allow entries in BO caches to be freed
      crypto: tegra - Don't touch bo refcount in host1x bo pin/unpin

 drivers/crypto/tegra/tegra-se-main.c |  3 +-
 drivers/gpu/drm/tegra/gem.c          | 13 ++------
 drivers/gpu/drm/tegra/submit.c       |  3 +-
 drivers/gpu/host1x/bus.c             | 60 +++++++++++++++++++++++++++++++++++-
 include/linux/host1x.h               |  7 +++++
 5 files changed, 70 insertions(+), 16 deletions(-)
---
base-commit: 028ef9c96e96197026887c0f092424679298aae8
change-id: 20260513-host1x-bocache-leak-4759384eb792

[PATCH 1/2] gpu: host1x: Allow entries in BO caches to be freed

[Mikko Perttunen]

When a buffer object is pinned via host1x_bo_pin() with a cache, the
resulting mapping is kept in the cache so it can be reused on subsequent
pins. Each mapping held a reference to the underlying host1x_bo (taken
in tegra_bo_pin / gather_bo_pin), so as long as a mapping was cached,
the bo itself could not be freed.

However, the only way to remove the cached mapping was through the free
path of the buffer object. This meant that if a bo got cached, it could
never get freed again.

Resolve the circularity by holding a weak reference to the bo from the
cache side. This is done by having the .pin callbacks not bump the bo's
refcount -- instead the common Host1x bo code does so, except for the
cache reference.

Also move the remove-cache-mapping-on-free code into a common function
inside Host1x code. This is only called from the TegraDRM GEM buffers
since those are the only ones that can be cached at the moment.

Reported-by: Aaron Kling <webgeek1234@gmail.com>
Fixes: 1f39b1dfa53c ("drm/tegra: Implement buffer object cache")
Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
---
 drivers/gpu/drm/tegra/gem.c    | 13 ++-------
 drivers/gpu/drm/tegra/submit.c |  3 +--
 drivers/gpu/host1x/bus.c       | 60 +++++++++++++++++++++++++++++++++++++++++-
 include/linux/host1x.h         |  7 +++++
 4 files changed, 69 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
index d2bae88ad545..2377e2b76397 100644
--- a/drivers/gpu/drm/tegra/gem.c
+++ b/drivers/gpu/drm/tegra/gem.c
@@ -69,7 +69,7 @@ static struct host1x_bo_mapping *tegra_bo_pin(struct device *dev, struct host1x_
 		return ERR_PTR(-ENOMEM);
 
 	kref_init(&map->ref);
-	map->bo = host1x_bo_get(bo);
+	map->bo = bo;
 	map->direction = direction;
 	map->dev = dev;
 
@@ -170,7 +170,6 @@ static void tegra_bo_unpin(struct host1x_bo_mapping *map)
 		kfree(map->sgt);
 	}
 
-	host1x_bo_put(map->bo);
 	kfree(map);
 }
 
@@ -509,17 +508,9 @@ static struct tegra_bo *tegra_bo_import(struct drm_device *drm,
 void tegra_bo_free_object(struct drm_gem_object *gem)
 {
 	struct tegra_drm *tegra = gem->dev->dev_private;
-	struct host1x_bo_mapping *mapping, *tmp;
 	struct tegra_bo *bo = to_tegra_bo(gem);
 
-	/* remove all mappings of this buffer object from any caches */
-	list_for_each_entry_safe(mapping, tmp, &bo->base.mappings, list) {
-		if (mapping->cache)
-			host1x_bo_unpin(mapping);
-		else
-			dev_err(gem->dev->dev, "mapping %p stale for device %s\n", mapping,
-				dev_name(mapping->dev));
-	}
+	host1x_bo_clear_cached_mappings(&bo->base);
 
 	if (tegra->domain) {
 		tegra_bo_iommu_unmap(tegra, bo);
diff --git a/drivers/gpu/drm/tegra/submit.c b/drivers/gpu/drm/tegra/submit.c
index 3009b8b9e619..e5841857c937 100644
--- a/drivers/gpu/drm/tegra/submit.c
+++ b/drivers/gpu/drm/tegra/submit.c
@@ -76,7 +76,7 @@ gather_bo_pin(struct device *dev, struct host1x_bo *bo, enum dma_data_direction
 		return ERR_PTR(-ENOMEM);
 
 	kref_init(&map->ref);
-	map->bo = host1x_bo_get(bo);
+	map->bo = bo;
 	map->direction = direction;
 	map->dev = dev;
 
@@ -117,7 +117,6 @@ static void gather_bo_unpin(struct host1x_bo_mapping *map)
 	dma_unmap_sgtable(map->dev, map->sgt, map->direction, 0);
 	sg_free_table(map->sgt);
 	kfree(map->sgt);
-	host1x_bo_put(map->bo);
 
 	kfree(map);
 }
diff --git a/drivers/gpu/host1x/bus.c b/drivers/gpu/host1x/bus.c
index f814eb4941c0..772e05a7b45b 100644
--- a/drivers/gpu/host1x/bus.c
+++ b/drivers/gpu/host1x/bus.c
@@ -887,6 +887,20 @@ int host1x_client_resume(struct host1x_client *client)
 }
 EXPORT_SYMBOL(host1x_client_resume);
 
+/**
+ * host1x_bo_pin() - Create a DMA mapping for the buffer object
+ * @dev: Device onto which DMA map to
+ * @bo: Buffer object to map
+ * @dir: DMA direction
+ * @cache: Cache in which to store mapping, or NULL
+ *
+ * Creates a DMA mapping pointing to @bo for @dev. The refcount of @bo is incremented
+ * until host1x_bo_unpin is called.
+ *
+ * If @cache is specified, the mapping is also stored in the cache and not released
+ * until @bo is freed (refcount drops to zero). This improves performance when a buffer
+ * is pinned and unpinned frequently as in the case of display use.
+ */
 struct host1x_bo_mapping *host1x_bo_pin(struct device *dev, struct host1x_bo *bo,
 					enum dma_data_direction dir,
 					struct host1x_bo_cache *cache)
@@ -899,6 +913,7 @@ struct host1x_bo_mapping *host1x_bo_pin(struct device *dev, struct host1x_bo *bo
 		list_for_each_entry(mapping, &cache->mappings, entry) {
 			if (mapping->bo == bo && mapping->direction == dir) {
 				kref_get(&mapping->ref);
+				host1x_bo_get(bo);
 				goto unlock;
 			}
 		}
@@ -908,6 +923,8 @@ struct host1x_bo_mapping *host1x_bo_pin(struct device *dev, struct host1x_bo *bo
 	if (IS_ERR(mapping))
 		goto unlock;
 
+	host1x_bo_get(bo);
+
 	spin_lock(&mapping->bo->lock);
 	list_add_tail(&mapping->list, &bo->mappings);
 	spin_unlock(&mapping->bo->lock);
@@ -918,7 +935,12 @@ struct host1x_bo_mapping *host1x_bo_pin(struct device *dev, struct host1x_bo *bo
 
 		list_add_tail(&mapping->entry, &cache->mappings);
 
-		/* bump reference count to track the copy in the cache */
+		/*
+		 * Bump the mapping reference count to track the mapping in the cache,
+		 * but do not bump the BO's refcount. This allows the BO to still get freed,
+		 * triggering the release of the cache mapping through
+		 * host1x_bo_clear_cached_mappings.
+		 */
 		kref_get(&mapping->ref);
 	}
 
@@ -948,9 +970,17 @@ static void __host1x_bo_unpin(struct kref *ref)
 	mapping->bo->ops->unpin(mapping);
 }
 
+/**
+ * host1x_bo_unpin() - Release an established DMA mapping of a buffer object
+ * @mapping: Mapping to release
+ *
+ * Unmaps the given @mapping, unless it is cached. Decreases the refcount on
+ * the underlying buffer object.
+ */
 void host1x_bo_unpin(struct host1x_bo_mapping *mapping)
 {
 	struct host1x_bo_cache *cache = mapping->cache;
+	struct host1x_bo *bo = mapping->bo;
 
 	if (cache)
 		mutex_lock(&cache->lock);
@@ -959,5 +989,33 @@ void host1x_bo_unpin(struct host1x_bo_mapping *mapping)
 
 	if (cache)
 		mutex_unlock(&cache->lock);
+
+	host1x_bo_put(bo);
 }
 EXPORT_SYMBOL(host1x_bo_unpin);
+
+/**
+ * host1x_bo_clear_cached_mappings() - Remove all cached mappings pointing at a bo
+ * @bo: Buffer object to release mappings of
+ *
+ * Drops references to any mappings pointing to @bo left in any caches. This must
+ * be called by any host1x_bo implementers that may be pinned with caching enabled
+ * before freeing the bo.
+ */
+void host1x_bo_clear_cached_mappings(struct host1x_bo *bo)
+{
+	struct host1x_bo_mapping *mapping, *tmp;
+	struct host1x_bo_cache *cache;
+
+	list_for_each_entry_safe(mapping, tmp, &bo->mappings, list) {
+		cache = mapping->cache;
+		if (WARN_ON(!cache))
+			continue;
+
+		mutex_lock(&mapping->cache->lock);
+		WARN_ON(kref_read(&mapping->ref) != 1);
+		__host1x_bo_unpin(&mapping->ref);
+		mutex_unlock(&mapping->cache->lock);
+	}
+}
+EXPORT_SYMBOL(host1x_bo_clear_cached_mappings);
diff --git a/include/linux/host1x.h b/include/linux/host1x.h
index 5e7a63143a4a..d8f052a85b75 100644
--- a/include/linux/host1x.h
+++ b/include/linux/host1x.h
@@ -143,6 +143,12 @@ static inline struct host1x_bo_mapping *to_host1x_bo_mapping(struct kref *ref)
 	return container_of(ref, struct host1x_bo_mapping, ref);
 }
 
+/**
+ * struct host1x_bo_ops - operations implemented by a host1x_bo provider
+ *
+ * @pin: create a DMA mapping. Implementation must not touch the bo's refcount.
+ * @unpin: destroy a DMA mapping. Implementation must not touch the bo's refcount.
+ */
 struct host1x_bo_ops {
 	struct host1x_bo *(*get)(struct host1x_bo *bo);
 	void (*put)(struct host1x_bo *bo);
@@ -181,6 +187,7 @@ struct host1x_bo_mapping *host1x_bo_pin(struct device *dev, struct host1x_bo *bo
 					enum dma_data_direction dir,
 					struct host1x_bo_cache *cache);
 void host1x_bo_unpin(struct host1x_bo_mapping *map);
+void host1x_bo_clear_cached_mappings(struct host1x_bo *bo);
 
 static inline void *host1x_bo_mmap(struct host1x_bo *bo)
 {

-- 
2.53.0

[PATCH 2/2] crypto: tegra - Don't touch bo refcount in host1x bo pin/unpin

[Mikko Perttunen]

Since commit "gpu: host1x: Allow entries in BO caches to be freed",
host1x_bo_pin() and host1x_bo_unpin() handle the bo's refcount
themselves. .pin/.unpin callbacks should not adjust it.

Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
---
 drivers/crypto/tegra/tegra-se-main.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/crypto/tegra/tegra-se-main.c b/drivers/crypto/tegra/tegra-se-main.c
index eb71113ed146..d7541a9c0a92 100644
--- a/drivers/crypto/tegra/tegra-se-main.c
+++ b/drivers/crypto/tegra/tegra-se-main.c
@@ -52,7 +52,7 @@ tegra_se_cmdbuf_pin(struct device *dev, struct host1x_bo *bo, enum dma_data_dire
 		return ERR_PTR(-ENOMEM);
 
 	kref_init(&map->ref);
-	map->bo = host1x_bo_get(bo);
+	map->bo = bo;
 	map->direction = direction;
 	map->dev = dev;
 
@@ -93,7 +93,6 @@ static void tegra_se_cmdbuf_unpin(struct host1x_bo_mapping *map)
 	dma_unmap_sgtable(map->dev, map->sgt, map->direction, 0);
 	sg_free_table(map->sgt);
 	kfree(map->sgt);
-	host1x_bo_put(map->bo);
 
 	kfree(map);
 }

-- 
2.53.0

Re: [PATCH 1/2] gpu: host1x: Allow entries in BO caches to be freed

[Aaron Kling]

On Thu, May 14, 2026 at 9:35 PM Mikko Perttunen <mperttunen@nvidia.com> wrote:
>
> When a buffer object is pinned via host1x_bo_pin() with a cache, the
> resulting mapping is kept in the cache so it can be reused on subsequent
> pins. Each mapping held a reference to the underlying host1x_bo (taken
> in tegra_bo_pin / gather_bo_pin), so as long as a mapping was cached,
> the bo itself could not be freed.
>
> However, the only way to remove the cached mapping was through the free
> path of the buffer object. This meant that if a bo got cached, it could
> never get freed again.
>
> Resolve the circularity by holding a weak reference to the bo from the
> cache side. This is done by having the .pin callbacks not bump the bo's
> refcount -- instead the common Host1x bo code does so, except for the
> cache reference.
>
> Also move the remove-cache-mapping-on-free code into a common function
> inside Host1x code. This is only called from the TegraDRM GEM buffers
> since those are the only ones that can be cached at the moment.
>
> Reported-by: Aaron Kling <webgeek1234@gmail.com>
> Fixes: 1f39b1dfa53c ("drm/tegra: Implement buffer object cache")
> Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
> ---
>  drivers/gpu/drm/tegra/gem.c    | 13 ++-------
>  drivers/gpu/drm/tegra/submit.c |  3 +--
>  drivers/gpu/host1x/bus.c       | 60 +++++++++++++++++++++++++++++++++++++++++-
>  include/linux/host1x.h         |  7 +++++
>  4 files changed, 69 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
> index d2bae88ad545..2377e2b76397 100644
> --- a/drivers/gpu/drm/tegra/gem.c
> +++ b/drivers/gpu/drm/tegra/gem.c
> @@ -69,7 +69,7 @@ static struct host1x_bo_mapping *tegra_bo_pin(struct device *dev, struct host1x_
>                 return ERR_PTR(-ENOMEM);
>
>         kref_init(&map->ref);
> -       map->bo = host1x_bo_get(bo);
> +       map->bo = bo;
>         map->direction = direction;
>         map->dev = dev;
>
> @@ -170,7 +170,6 @@ static void tegra_bo_unpin(struct host1x_bo_mapping *map)
>                 kfree(map->sgt);
>         }
>
> -       host1x_bo_put(map->bo);
>         kfree(map);
>  }
>
> @@ -509,17 +508,9 @@ static struct tegra_bo *tegra_bo_import(struct drm_device *drm,
>  void tegra_bo_free_object(struct drm_gem_object *gem)
>  {
>         struct tegra_drm *tegra = gem->dev->dev_private;
> -       struct host1x_bo_mapping *mapping, *tmp;
>         struct tegra_bo *bo = to_tegra_bo(gem);
>
> -       /* remove all mappings of this buffer object from any caches */
> -       list_for_each_entry_safe(mapping, tmp, &bo->base.mappings, list) {
> -               if (mapping->cache)
> -                       host1x_bo_unpin(mapping);
> -               else
> -                       dev_err(gem->dev->dev, "mapping %p stale for device %s\n", mapping,
> -                               dev_name(mapping->dev));
> -       }
> +       host1x_bo_clear_cached_mappings(&bo->base);
>
>         if (tegra->domain) {
>                 tegra_bo_iommu_unmap(tegra, bo);
> diff --git a/drivers/gpu/drm/tegra/submit.c b/drivers/gpu/drm/tegra/submit.c
> index 3009b8b9e619..e5841857c937 100644
> --- a/drivers/gpu/drm/tegra/submit.c
> +++ b/drivers/gpu/drm/tegra/submit.c
> @@ -76,7 +76,7 @@ gather_bo_pin(struct device *dev, struct host1x_bo *bo, enum dma_data_direction
>                 return ERR_PTR(-ENOMEM);
>
>         kref_init(&map->ref);
> -       map->bo = host1x_bo_get(bo);
> +       map->bo = bo;
>         map->direction = direction;
>         map->dev = dev;
>
> @@ -117,7 +117,6 @@ static void gather_bo_unpin(struct host1x_bo_mapping *map)
>         dma_unmap_sgtable(map->dev, map->sgt, map->direction, 0);
>         sg_free_table(map->sgt);
>         kfree(map->sgt);
> -       host1x_bo_put(map->bo);
>
>         kfree(map);
>  }
> diff --git a/drivers/gpu/host1x/bus.c b/drivers/gpu/host1x/bus.c
> index f814eb4941c0..772e05a7b45b 100644
> --- a/drivers/gpu/host1x/bus.c
> +++ b/drivers/gpu/host1x/bus.c
> @@ -887,6 +887,20 @@ int host1x_client_resume(struct host1x_client *client)
>  }
>  EXPORT_SYMBOL(host1x_client_resume);
>
> +/**
> + * host1x_bo_pin() - Create a DMA mapping for the buffer object
> + * @dev: Device onto which DMA map to
> + * @bo: Buffer object to map
> + * @dir: DMA direction
> + * @cache: Cache in which to store mapping, or NULL
> + *
> + * Creates a DMA mapping pointing to @bo for @dev. The refcount of @bo is incremented
> + * until host1x_bo_unpin is called.
> + *
> + * If @cache is specified, the mapping is also stored in the cache and not released
> + * until @bo is freed (refcount drops to zero). This improves performance when a buffer
> + * is pinned and unpinned frequently as in the case of display use.
> + */
>  struct host1x_bo_mapping *host1x_bo_pin(struct device *dev, struct host1x_bo *bo,
>                                         enum dma_data_direction dir,
>                                         struct host1x_bo_cache *cache)
> @@ -899,6 +913,7 @@ struct host1x_bo_mapping *host1x_bo_pin(struct device *dev, struct host1x_bo *bo
>                 list_for_each_entry(mapping, &cache->mappings, entry) {
>                         if (mapping->bo == bo && mapping->direction == dir) {
>                                 kref_get(&mapping->ref);
> +                               host1x_bo_get(bo);
>                                 goto unlock;
>                         }
>                 }
> @@ -908,6 +923,8 @@ struct host1x_bo_mapping *host1x_bo_pin(struct device *dev, struct host1x_bo *bo
>         if (IS_ERR(mapping))
>                 goto unlock;
>
> +       host1x_bo_get(bo);
> +
>         spin_lock(&mapping->bo->lock);
>         list_add_tail(&mapping->list, &bo->mappings);
>         spin_unlock(&mapping->bo->lock);
> @@ -918,7 +935,12 @@ struct host1x_bo_mapping *host1x_bo_pin(struct device *dev, struct host1x_bo *bo
>
>                 list_add_tail(&mapping->entry, &cache->mappings);
>
> -               /* bump reference count to track the copy in the cache */
> +               /*
> +                * Bump the mapping reference count to track the mapping in the cache,
> +                * but do not bump the BO's refcount. This allows the BO to still get freed,
> +                * triggering the release of the cache mapping through
> +                * host1x_bo_clear_cached_mappings.
> +                */
>                 kref_get(&mapping->ref);
>         }
>
> @@ -948,9 +970,17 @@ static void __host1x_bo_unpin(struct kref *ref)
>         mapping->bo->ops->unpin(mapping);
>  }
>
> +/**
> + * host1x_bo_unpin() - Release an established DMA mapping of a buffer object
> + * @mapping: Mapping to release
> + *
> + * Unmaps the given @mapping, unless it is cached. Decreases the refcount on
> + * the underlying buffer object.
> + */
>  void host1x_bo_unpin(struct host1x_bo_mapping *mapping)
>  {
>         struct host1x_bo_cache *cache = mapping->cache;
> +       struct host1x_bo *bo = mapping->bo;
>
>         if (cache)
>                 mutex_lock(&cache->lock);
> @@ -959,5 +989,33 @@ void host1x_bo_unpin(struct host1x_bo_mapping *mapping)
>
>         if (cache)
>                 mutex_unlock(&cache->lock);
> +
> +       host1x_bo_put(bo);
>  }
>  EXPORT_SYMBOL(host1x_bo_unpin);
> +
> +/**
> + * host1x_bo_clear_cached_mappings() - Remove all cached mappings pointing at a bo
> + * @bo: Buffer object to release mappings of
> + *
> + * Drops references to any mappings pointing to @bo left in any caches. This must
> + * be called by any host1x_bo implementers that may be pinned with caching enabled
> + * before freeing the bo.
> + */
> +void host1x_bo_clear_cached_mappings(struct host1x_bo *bo)
> +{
> +       struct host1x_bo_mapping *mapping, *tmp;
> +       struct host1x_bo_cache *cache;
> +
> +       list_for_each_entry_safe(mapping, tmp, &bo->mappings, list) {
> +               cache = mapping->cache;
> +               if (WARN_ON(!cache))
> +                       continue;
> +
> +               mutex_lock(&mapping->cache->lock);
> +               WARN_ON(kref_read(&mapping->ref) != 1);
> +               __host1x_bo_unpin(&mapping->ref);
> +               mutex_unlock(&mapping->cache->lock);
> +       }
> +}
> +EXPORT_SYMBOL(host1x_bo_clear_cached_mappings);
> diff --git a/include/linux/host1x.h b/include/linux/host1x.h
> index 5e7a63143a4a..d8f052a85b75 100644
> --- a/include/linux/host1x.h
> +++ b/include/linux/host1x.h
> @@ -143,6 +143,12 @@ static inline struct host1x_bo_mapping *to_host1x_bo_mapping(struct kref *ref)
>         return container_of(ref, struct host1x_bo_mapping, ref);
>  }
>
> +/**
> + * struct host1x_bo_ops - operations implemented by a host1x_bo provider
> + *
> + * @pin: create a DMA mapping. Implementation must not touch the bo's refcount.
> + * @unpin: destroy a DMA mapping. Implementation must not touch the bo's refcount.
> + */
>  struct host1x_bo_ops {
>         struct host1x_bo *(*get)(struct host1x_bo *bo);
>         void (*put)(struct host1x_bo *bo);
> @@ -181,6 +187,7 @@ struct host1x_bo_mapping *host1x_bo_pin(struct device *dev, struct host1x_bo *bo
>                                         enum dma_data_direction dir,
>                                         struct host1x_bo_cache *cache);
>  void host1x_bo_unpin(struct host1x_bo_mapping *map);
> +void host1x_bo_clear_cached_mappings(struct host1x_bo *bo);
>
>  static inline void *host1x_bo_mmap(struct host1x_bo *bo)
>  {
>
> --
> 2.53.0
>

I have verified this on a Jetson AGX Xavier devkit, a Jetson Xavier NX
devkit, a Jetson TX2 devkit, and a Jetson TX2 NX in a p3509 carrier.
No longer seeing allocation failures nor am I seeing any obvious
regressions. I am currently unable to boot any t210 device to Android
userspace to verify those for various preexisting reasons, and Android
recovery does not reallocate buffers to stress this issue.

Tested-by: Aaron Kling <webgeek1234@gmail.com>

Aaron

Re: [PATCH 1/2] gpu: host1x: Allow entries in BO caches to be freed

[Mikko Perttunen]

On Monday, May 18, 2026 5:02 AM Aaron Kling wrote:
> On Thu, May 14, 2026 at 9:35 PM Mikko Perttunen <mperttunen@nvidia.com> wrote:
> >
> > When a buffer object is pinned via host1x_bo_pin() with a cache, the
> > resulting mapping is kept in the cache so it can be reused on subsequent
> > pins. Each mapping held a reference to the underlying host1x_bo (taken
> > in tegra_bo_pin / gather_bo_pin), so as long as a mapping was cached,
> > the bo itself could not be freed.
> >
> > However, the only way to remove the cached mapping was through the free
> > path of the buffer object. This meant that if a bo got cached, it could
> > never get freed again.
> >
> > Resolve the circularity by holding a weak reference to the bo from the
> > cache side. This is done by having the .pin callbacks not bump the bo's
> > refcount -- instead the common Host1x bo code does so, except for the
> > cache reference.
> >
> > Also move the remove-cache-mapping-on-free code into a common function
> > inside Host1x code. This is only called from the TegraDRM GEM buffers
> > since those are the only ones that can be cached at the moment.
> >
> > Reported-by: Aaron Kling <webgeek1234@gmail.com>
> > Fixes: 1f39b1dfa53c ("drm/tegra: Implement buffer object cache")
> > Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
> > ---
> >  drivers/gpu/drm/tegra/gem.c    | 13 ++-------
> >  drivers/gpu/drm/tegra/submit.c |  3 +--
> >  drivers/gpu/host1x/bus.c       | 60 +++++++++++++++++++++++++++++++++++++++++-
> >  include/linux/host1x.h         |  7 +++++
> >  4 files changed, 69 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
> > index d2bae88ad545..2377e2b76397 100644
> > --- a/drivers/gpu/drm/tegra/gem.c
> > +++ b/drivers/gpu/drm/tegra/gem.c
> > @@ -69,7 +69,7 @@ static struct host1x_bo_mapping *tegra_bo_pin(struct device *dev, struct host1x_
> >                 return ERR_PTR(-ENOMEM);
> >
> >         kref_init(&map->ref);
> > -       map->bo = host1x_bo_get(bo);
> > +       map->bo = bo;
> >         map->direction = direction;
> >         map->dev = dev;
> >
> > @@ -170,7 +170,6 @@ static void tegra_bo_unpin(struct host1x_bo_mapping *map)
> >                 kfree(map->sgt);
> >         }
> >
> > -       host1x_bo_put(map->bo);
> >         kfree(map);
> >  }
> >
> > @@ -509,17 +508,9 @@ static struct tegra_bo *tegra_bo_import(struct drm_device *drm,
> >  void tegra_bo_free_object(struct drm_gem_object *gem)
> >  {
> >         struct tegra_drm *tegra = gem->dev->dev_private;
> > -       struct host1x_bo_mapping *mapping, *tmp;
> >         struct tegra_bo *bo = to_tegra_bo(gem);
> >
> > -       /* remove all mappings of this buffer object from any caches */
> > -       list_for_each_entry_safe(mapping, tmp, &bo->base.mappings, list) {
> > -               if (mapping->cache)
> > -                       host1x_bo_unpin(mapping);
> > -               else
> > -                       dev_err(gem->dev->dev, "mapping %p stale for device %s\n", mapping,
> > -                               dev_name(mapping->dev));
> > -       }
> > +       host1x_bo_clear_cached_mappings(&bo->base);
> >
> >         if (tegra->domain) {
> >                 tegra_bo_iommu_unmap(tegra, bo);
> > diff --git a/drivers/gpu/drm/tegra/submit.c b/drivers/gpu/drm/tegra/submit.c
> > index 3009b8b9e619..e5841857c937 100644
> > --- a/drivers/gpu/drm/tegra/submit.c
> > +++ b/drivers/gpu/drm/tegra/submit.c
> > @@ -76,7 +76,7 @@ gather_bo_pin(struct device *dev, struct host1x_bo *bo, enum dma_data_direction
> >                 return ERR_PTR(-ENOMEM);
> >
> >         kref_init(&map->ref);
> > -       map->bo = host1x_bo_get(bo);
> > +       map->bo = bo;
> >         map->direction = direction;
> >         map->dev = dev;
> >
> > @@ -117,7 +117,6 @@ static void gather_bo_unpin(struct host1x_bo_mapping *map)
> >         dma_unmap_sgtable(map->dev, map->sgt, map->direction, 0);
> >         sg_free_table(map->sgt);
> >         kfree(map->sgt);
> > -       host1x_bo_put(map->bo);
> >
> >         kfree(map);
> >  }
> > diff --git a/drivers/gpu/host1x/bus.c b/drivers/gpu/host1x/bus.c
> > index f814eb4941c0..772e05a7b45b 100644
> > --- a/drivers/gpu/host1x/bus.c
> > +++ b/drivers/gpu/host1x/bus.c
> > @@ -887,6 +887,20 @@ int host1x_client_resume(struct host1x_client *client)
> >  }
> >  EXPORT_SYMBOL(host1x_client_resume);
> >
> > +/**
> > + * host1x_bo_pin() - Create a DMA mapping for the buffer object
> > + * @dev: Device onto which DMA map to
> > + * @bo: Buffer object to map
> > + * @dir: DMA direction
> > + * @cache: Cache in which to store mapping, or NULL
> > + *
> > + * Creates a DMA mapping pointing to @bo for @dev. The refcount of @bo is incremented
> > + * until host1x_bo_unpin is called.
> > + *
> > + * If @cache is specified, the mapping is also stored in the cache and not released
> > + * until @bo is freed (refcount drops to zero). This improves performance when a buffer
> > + * is pinned and unpinned frequently as in the case of display use.
> > + */
> >  struct host1x_bo_mapping *host1x_bo_pin(struct device *dev, struct host1x_bo *bo,
> >                                         enum dma_data_direction dir,
> >                                         struct host1x_bo_cache *cache)
> > @@ -899,6 +913,7 @@ struct host1x_bo_mapping *host1x_bo_pin(struct device *dev, struct host1x_bo *bo
> >                 list_for_each_entry(mapping, &cache->mappings, entry) {
> >                         if (mapping->bo == bo && mapping->direction == dir) {
> >                                 kref_get(&mapping->ref);
> > +                               host1x_bo_get(bo);
> >                                 goto unlock;
> >                         }
> >                 }
> > @@ -908,6 +923,8 @@ struct host1x_bo_mapping *host1x_bo_pin(struct device *dev, struct host1x_bo *bo
> >         if (IS_ERR(mapping))
> >                 goto unlock;
> >
> > +       host1x_bo_get(bo);
> > +
> >         spin_lock(&mapping->bo->lock);
> >         list_add_tail(&mapping->list, &bo->mappings);
> >         spin_unlock(&mapping->bo->lock);
> > @@ -918,7 +935,12 @@ struct host1x_bo_mapping *host1x_bo_pin(struct device *dev, struct host1x_bo *bo
> >
> >                 list_add_tail(&mapping->entry, &cache->mappings);
> >
> > -               /* bump reference count to track the copy in the cache */
> > +               /*
> > +                * Bump the mapping reference count to track the mapping in the cache,
> > +                * but do not bump the BO's refcount. This allows the BO to still get freed,
> > +                * triggering the release of the cache mapping through
> > +                * host1x_bo_clear_cached_mappings.
> > +                */
> >                 kref_get(&mapping->ref);
> >         }
> >
> > @@ -948,9 +970,17 @@ static void __host1x_bo_unpin(struct kref *ref)
> >         mapping->bo->ops->unpin(mapping);
> >  }
> >
> > +/**
> > + * host1x_bo_unpin() - Release an established DMA mapping of a buffer object
> > + * @mapping: Mapping to release
> > + *
> > + * Unmaps the given @mapping, unless it is cached. Decreases the refcount on
> > + * the underlying buffer object.
> > + */
> >  void host1x_bo_unpin(struct host1x_bo_mapping *mapping)
> >  {
> >         struct host1x_bo_cache *cache = mapping->cache;
> > +       struct host1x_bo *bo = mapping->bo;
> >
> >         if (cache)
> >                 mutex_lock(&cache->lock);
> > @@ -959,5 +989,33 @@ void host1x_bo_unpin(struct host1x_bo_mapping *mapping)
> >
> >         if (cache)
> >                 mutex_unlock(&cache->lock);
> > +
> > +       host1x_bo_put(bo);
> >  }
> >  EXPORT_SYMBOL(host1x_bo_unpin);
> > +
> > +/**
> > + * host1x_bo_clear_cached_mappings() - Remove all cached mappings pointing at a bo
> > + * @bo: Buffer object to release mappings of
> > + *
> > + * Drops references to any mappings pointing to @bo left in any caches. This must
> > + * be called by any host1x_bo implementers that may be pinned with caching enabled
> > + * before freeing the bo.
> > + */
> > +void host1x_bo_clear_cached_mappings(struct host1x_bo *bo)
> > +{
> > +       struct host1x_bo_mapping *mapping, *tmp;
> > +       struct host1x_bo_cache *cache;
> > +
> > +       list_for_each_entry_safe(mapping, tmp, &bo->mappings, list) {
> > +               cache = mapping->cache;
> > +               if (WARN_ON(!cache))
> > +                       continue;
> > +
> > +               mutex_lock(&mapping->cache->lock);
> > +               WARN_ON(kref_read(&mapping->ref) != 1);
> > +               __host1x_bo_unpin(&mapping->ref);
> > +               mutex_unlock(&mapping->cache->lock);
> > +       }
> > +}
> > +EXPORT_SYMBOL(host1x_bo_clear_cached_mappings);
> > diff --git a/include/linux/host1x.h b/include/linux/host1x.h
> > index 5e7a63143a4a..d8f052a85b75 100644
> > --- a/include/linux/host1x.h
> > +++ b/include/linux/host1x.h
> > @@ -143,6 +143,12 @@ static inline struct host1x_bo_mapping *to_host1x_bo_mapping(struct kref *ref)
> >         return container_of(ref, struct host1x_bo_mapping, ref);
> >  }
> >
> > +/**
> > + * struct host1x_bo_ops - operations implemented by a host1x_bo provider
> > + *
> > + * @pin: create a DMA mapping. Implementation must not touch the bo's refcount.
> > + * @unpin: destroy a DMA mapping. Implementation must not touch the bo's refcount.
> > + */
> >  struct host1x_bo_ops {
> >         struct host1x_bo *(*get)(struct host1x_bo *bo);
> >         void (*put)(struct host1x_bo *bo);
> > @@ -181,6 +187,7 @@ struct host1x_bo_mapping *host1x_bo_pin(struct device *dev, struct host1x_bo *bo
> >                                         enum dma_data_direction dir,
> >                                         struct host1x_bo_cache *cache);
> >  void host1x_bo_unpin(struct host1x_bo_mapping *map);
> > +void host1x_bo_clear_cached_mappings(struct host1x_bo *bo);
> >
> >  static inline void *host1x_bo_mmap(struct host1x_bo *bo)
> >  {
> >
> > --
> > 2.53.0
> >
> 
> I have verified this on a Jetson AGX Xavier devkit, a Jetson Xavier NX
> devkit, a Jetson TX2 devkit, and a Jetson TX2 NX in a p3509 carrier.
> No longer seeing allocation failures nor am I seeing any obvious
> regressions. I am currently unable to boot any t210 device to Android
> userspace to verify those for various preexisting reasons, and Android
> recovery does not reallocate buffers to stress this issue.
> 
> Tested-by: Aaron Kling <webgeek1234@gmail.com>
> 
> Aaron

Thank you!

Re: [PATCH 2/2] crypto: tegra - Don't touch bo refcount in host1x bo pin/unpin

[Herbert Xu]

On Fri, May 15, 2026 at 11:34:52AM +0900, Mikko Perttunen wrote:
> Since commit "gpu: host1x: Allow entries in BO caches to be freed",
> host1x_bo_pin() and host1x_bo_unpin() handle the bo's refcount
> themselves. .pin/.unpin callbacks should not adjust it.
> 
> Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
> ---
>  drivers/crypto/tegra/tegra-se-main.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)

Patch applied.  Thanks.
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Re: [PATCH 1/2] gpu: host1x: Allow entries in BO caches to be freed

[Thierry Reding]

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On Fri, May 15, 2026 at 11:34:51AM +0900, Mikko Perttunen wrote:
> When a buffer object is pinned via host1x_bo_pin() with a cache, the
> resulting mapping is kept in the cache so it can be reused on subsequent
> pins. Each mapping held a reference to the underlying host1x_bo (taken
> in tegra_bo_pin / gather_bo_pin), so as long as a mapping was cached,
> the bo itself could not be freed.
> 
> However, the only way to remove the cached mapping was through the free
> path of the buffer object. This meant that if a bo got cached, it could
> never get freed again.
> 
> Resolve the circularity by holding a weak reference to the bo from the
> cache side. This is done by having the .pin callbacks not bump the bo's
> refcount -- instead the common Host1x bo code does so, except for the
> cache reference.
> 
> Also move the remove-cache-mapping-on-free code into a common function
> inside Host1x code. This is only called from the TegraDRM GEM buffers
> since those are the only ones that can be cached at the moment.
> 
> Reported-by: Aaron Kling <webgeek1234@gmail.com>
> Fixes: 1f39b1dfa53c ("drm/tegra: Implement buffer object cache")
> Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
> ---
>  drivers/gpu/drm/tegra/gem.c    | 13 ++-------
>  drivers/gpu/drm/tegra/submit.c |  3 +--
>  drivers/gpu/host1x/bus.c       | 60 +++++++++++++++++++++++++++++++++++++++++-
>  include/linux/host1x.h         |  7 +++++
>  4 files changed, 69 insertions(+), 14 deletions(-)

Applied, thanks.

Thierry

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