Add the drm_gem_huge_mnt_create() helper to avoid code duplication in
the i915, V3D, Panfrost and Panthor drivers. It creates and mounts a
dedicated huge tmpfs mountpoint, for the lifetime of a drm device,
used at GEM object initialization.

The next commits will port drivers to this helper.

v3:
- store huge tmpfs mountpoint in drm_device

Signed-off-by: Loïc Molinari <loic.molinari@collabora.com>
---
 drivers/gpu/drm/drm_gem.c | 67 +++++++++++++++++++++++++++++++++++++++
 include/drm/drm_device.h  | 11 +++++++
 include/drm/drm_gem.h     |  1 +
 3 files changed, 79 insertions(+)

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index f5a10ff363c9..b4e4947210ef 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -29,6 +29,7 @@
 #include <linux/export.h>
 #include <linux/file.h>
 #include <linux/fs.h>
+#include <linux/fs_context.h>
 #include <linux/iosys-map.h>
 #include <linux/mem_encrypt.h>
 #include <linux/mm.h>
@@ -82,6 +83,72 @@
  * up at a later date, and as our interface with shmfs for memory allocation.
  */
 
+static int drm_gem_add_fc_param(struct fs_context *fc, const char *key,
+				const char *value)
+{
+	return vfs_parse_fs_string(fc, key, value, strlen(value));
+}
+
+static void drm_gem_huge_mnt_free(struct drm_device *dev, void *data)
+{
+	drm_WARN_ON(dev, dev->huge_mnt == NULL);
+
+	kern_unmount(dev->huge_mnt);
+	dev->huge_mnt = NULL;
+}
+
+/**
+ * drm_gem_huge_mnt_create - Create, mount and use a huge tmpfs mountpoint
+ * @dev: drm_device a huge tmpfs mountpoint should be used with
+ * @value: huge tmpfs mount option value
+ *
+ * This function creates and mounts a dedicated huge tmpfs mountpoint for the
+ * lifetime of the drm device @dev which is used at GEM object initialization
+ * with drm_gem_object_init().
+ *
+ * The most common option value @value is "within_size" which only allocates
+ * huge pages if the page will be fully within the GEM object size. "always",
+ * "advise" and "never" are supported too but the latter would just create a
+ * mountpoint similar to the default one (`shm_mnt`). See shmemfs and
+ * Transparent Hugepage for more information.
+ *
+ * Returns:
+ * 0 on success or a negative error code on failure. Returns -EEXIST if called
+ * more than once for the lifetime of the drm device.
+ */
+int drm_gem_huge_mnt_create(struct drm_device *dev, const char *value)
+{
+	struct file_system_type *type;
+	struct fs_context *fc;
+	int ret;
+
+	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
+		return -EOPNOTSUPP;
+
+	type = get_fs_type("tmpfs");
+	if (unlikely(!type))
+		return -EOPNOTSUPP;
+
+	if (unlikely(dev->huge_mnt))
+		return -EEXIST;
+
+	fc = fs_context_for_mount(type, SB_KERNMOUNT);
+	if (IS_ERR(fc))
+		return PTR_ERR(fc);
+	ret = drm_gem_add_fc_param(fc, "source", "tmpfs");
+	if (unlikely(ret))
+		return -ENOPARAM;
+	ret = drm_gem_add_fc_param(fc, "huge", value);
+	if (unlikely(ret))
+		return -ENOPARAM;
+
+	dev->huge_mnt = fc_mount_longterm(fc);
+	put_fs_context(fc);
+
+	return drmm_add_action_or_reset(dev, drm_gem_huge_mnt_free, NULL);
+}
+EXPORT_SYMBOL_GPL(drm_gem_huge_mnt_create);
+
 static void
 drm_gem_init_release(struct drm_device *dev, void *ptr)
 {
diff --git a/include/drm/drm_device.h b/include/drm/drm_device.h
index 59fd3f4d5995..895b0ced972e 100644
--- a/include/drm/drm_device.h
+++ b/include/drm/drm_device.h
@@ -3,6 +3,7 @@
 
 #include <linux/list.h>
 #include <linux/kref.h>
+#include <linux/mount.h>
 #include <linux/mutex.h>
 #include <linux/idr.h>
 #include <linux/sched.h>
@@ -168,6 +169,16 @@ struct drm_device {
 	 */
 	struct drm_master *master;
 
+	/**
+	 * @huge_mnt:
+	 *
+	 * Huge tmpfs mountpoint used at GEM object initialization
+	 * drm_gem_object_init(). Drivers can call drm_gem_huge_mnt_create() to
+	 * create a huge tmfps mountpoint. The default tmpfs mountpoint
+	 * (`shm_mnt`) is used if NULL.
+	 */
+	struct vfsmount *huge_mnt;
+
 	/**
 	 * @driver_features: per-device driver features
 	 *
diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index 7c8bd67d087c..7285a62d9afc 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -492,6 +492,7 @@ struct drm_gem_object {
 		DRM_GEM_FOPS,\
 	}
 
+int drm_gem_huge_mnt_create(struct drm_device *dev, const char *value);
 void drm_gem_object_release(struct drm_gem_object *obj);
 void drm_gem_object_free(struct kref *kref);
 int drm_gem_object_init(struct drm_device *dev,
-- 
2.47.3

On Sat,  4 Oct 2025 11:30:46 +0200
Loïc Molinari <loic.molinari@collabora.com> wrote:

> Add the drm_gem_huge_mnt_create() helper to avoid code duplication in
> the i915, V3D, Panfrost and Panthor drivers. It creates and mounts a
> dedicated huge tmpfs mountpoint, for the lifetime of a drm device,
> used at GEM object initialization.
> 
> The next commits will port drivers to this helper.
> 
> v3:
> - store huge tmpfs mountpoint in drm_device
> 
> Signed-off-by: Loïc Molinari <loic.molinari@collabora.com>
> ---
>  drivers/gpu/drm/drm_gem.c | 67 +++++++++++++++++++++++++++++++++++++++
>  include/drm/drm_device.h  | 11 +++++++
>  include/drm/drm_gem.h     |  1 +
>  3 files changed, 79 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index f5a10ff363c9..b4e4947210ef 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -29,6 +29,7 @@
>  #include <linux/export.h>
>  #include <linux/file.h>
>  #include <linux/fs.h>
> +#include <linux/fs_context.h>
>  #include <linux/iosys-map.h>
>  #include <linux/mem_encrypt.h>
>  #include <linux/mm.h>
> @@ -82,6 +83,72 @@
>   * up at a later date, and as our interface with shmfs for memory allocation.
>   */
>  
> +static int drm_gem_add_fc_param(struct fs_context *fc, const char *key,
> +				const char *value)
> +{
> +	return vfs_parse_fs_string(fc, key, value, strlen(value));
> +}
> +
> +static void drm_gem_huge_mnt_free(struct drm_device *dev, void *data)
> +{
> +	drm_WARN_ON(dev, dev->huge_mnt == NULL);
> +
> +	kern_unmount(dev->huge_mnt);
> +	dev->huge_mnt = NULL;
> +}
> +
> +/**
> + * drm_gem_huge_mnt_create - Create, mount and use a huge tmpfs mountpoint
> + * @dev: drm_device a huge tmpfs mountpoint should be used with
> + * @value: huge tmpfs mount option value
> + *
> + * This function creates and mounts a dedicated huge tmpfs mountpoint for the
> + * lifetime of the drm device @dev which is used at GEM object initialization
> + * with drm_gem_object_init().
> + *
> + * The most common option value @value is "within_size" which only allocates
> + * huge pages if the page will be fully within the GEM object size. "always",
> + * "advise" and "never" are supported too but the latter would just create a
> + * mountpoint similar to the default one (`shm_mnt`). See shmemfs and
> + * Transparent Hugepage for more information.
> + *
> + * Returns:
> + * 0 on success or a negative error code on failure. Returns -EEXIST if called
> + * more than once for the lifetime of the drm device.
> + */
> +int drm_gem_huge_mnt_create(struct drm_device *dev, const char *value)
> +{
> +	struct file_system_type *type;
> +	struct fs_context *fc;
> +	int ret;
> +
> +	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
> +		return -EOPNOTSUPP;
> +
> +	type = get_fs_type("tmpfs");
> +	if (unlikely(!type))
> +		return -EOPNOTSUPP;
> +
> +	if (unlikely(dev->huge_mnt))
> +		return -EEXIST;

Do we even care about reporting an error when the huge mount point
already exists? Can we just return 0 in that case, which simplifies the
call sites since they don't have to check for EEXIST anymore.

> +
> +	fc = fs_context_for_mount(type, SB_KERNMOUNT);
> +	if (IS_ERR(fc))
> +		return PTR_ERR(fc);
> +	ret = drm_gem_add_fc_param(fc, "source", "tmpfs");
> +	if (unlikely(ret))
> +		return -ENOPARAM;
> +	ret = drm_gem_add_fc_param(fc, "huge", value);
> +	if (unlikely(ret))
> +		return -ENOPARAM;
> +
> +	dev->huge_mnt = fc_mount_longterm(fc);
> +	put_fs_context(fc);
> +
> +	return drmm_add_action_or_reset(dev, drm_gem_huge_mnt_free, NULL);
> +}
> +EXPORT_SYMBOL_GPL(drm_gem_huge_mnt_create);
> +
>  static void
>  drm_gem_init_release(struct drm_device *dev, void *ptr)
>  {
> diff --git a/include/drm/drm_device.h b/include/drm/drm_device.h
> index 59fd3f4d5995..895b0ced972e 100644
> --- a/include/drm/drm_device.h
> +++ b/include/drm/drm_device.h
> @@ -3,6 +3,7 @@
>  
>  #include <linux/list.h>
>  #include <linux/kref.h>
> +#include <linux/mount.h>
>  #include <linux/mutex.h>
>  #include <linux/idr.h>
>  #include <linux/sched.h>
> @@ -168,6 +169,16 @@ struct drm_device {
>  	 */
>  	struct drm_master *master;
>  
> +	/**
> +	 * @huge_mnt:
> +	 *
> +	 * Huge tmpfs mountpoint used at GEM object initialization
> +	 * drm_gem_object_init(). Drivers can call drm_gem_huge_mnt_create() to
> +	 * create a huge tmfps mountpoint. The default tmpfs mountpoint
> +	 * (`shm_mnt`) is used if NULL.
> +	 */
> +	struct vfsmount *huge_mnt;
> +
>  	/**
>  	 * @driver_features: per-device driver features
>  	 *
> diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
> index 7c8bd67d087c..7285a62d9afc 100644
> --- a/include/drm/drm_gem.h
> +++ b/include/drm/drm_gem.h
> @@ -492,6 +492,7 @@ struct drm_gem_object {
>  		DRM_GEM_FOPS,\
>  	}
>  
> +int drm_gem_huge_mnt_create(struct drm_device *dev, const char *value);
>  void drm_gem_object_release(struct drm_gem_object *obj);
>  void drm_gem_object_free(struct kref *kref);
>  int drm_gem_object_init(struct drm_device *dev,

On Sat,  4 Oct 2025 11:30:46 +0200
Loïc Molinari <loic.molinari@collabora.com> wrote:

> Add the drm_gem_huge_mnt_create() helper to avoid code duplication in
> the i915, V3D, Panfrost and Panthor drivers. It creates and mounts a
> dedicated huge tmpfs mountpoint, for the lifetime of a drm device,
> used at GEM object initialization.
> 
> The next commits will port drivers to this helper.
> 
> v3:
> - store huge tmpfs mountpoint in drm_device
> 
> Signed-off-by: Loïc Molinari <loic.molinari@collabora.com>
> ---
>  drivers/gpu/drm/drm_gem.c | 67 +++++++++++++++++++++++++++++++++++++++
>  include/drm/drm_device.h  | 11 +++++++
>  include/drm/drm_gem.h     |  1 +
>  3 files changed, 79 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index f5a10ff363c9..b4e4947210ef 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -29,6 +29,7 @@
>  #include <linux/export.h>
>  #include <linux/file.h>
>  #include <linux/fs.h>
> +#include <linux/fs_context.h>
>  #include <linux/iosys-map.h>
>  #include <linux/mem_encrypt.h>
>  #include <linux/mm.h>
> @@ -82,6 +83,72 @@
>   * up at a later date, and as our interface with shmfs for memory allocation.
>   */
>  
> +static int drm_gem_add_fc_param(struct fs_context *fc, const char *key,
> +				const char *value)
> +{
> +	return vfs_parse_fs_string(fc, key, value, strlen(value));
> +}
> +
> +static void drm_gem_huge_mnt_free(struct drm_device *dev, void *data)
> +{
> +	drm_WARN_ON(dev, dev->huge_mnt == NULL);
> +
> +	kern_unmount(dev->huge_mnt);
> +	dev->huge_mnt = NULL;
> +}
> +
> +/**
> + * drm_gem_huge_mnt_create - Create, mount and use a huge tmpfs mountpoint
> + * @dev: drm_device a huge tmpfs mountpoint should be used with
> + * @value: huge tmpfs mount option value
> + *
> + * This function creates and mounts a dedicated huge tmpfs mountpoint for the
> + * lifetime of the drm device @dev which is used at GEM object initialization
> + * with drm_gem_object_init().
> + *
> + * The most common option value @value is "within_size" which only allocates
> + * huge pages if the page will be fully within the GEM object size. "always",
> + * "advise" and "never" are supported too but the latter would just create a
> + * mountpoint similar to the default one (`shm_mnt`). See shmemfs and
> + * Transparent Hugepage for more information.
> + *
> + * Returns:
> + * 0 on success or a negative error code on failure. Returns -EEXIST if called
> + * more than once for the lifetime of the drm device.
> + */
> +int drm_gem_huge_mnt_create(struct drm_device *dev, const char *value)
> +{
> +	struct file_system_type *type;
> +	struct fs_context *fc;
> +	int ret;
> +
> +	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
> +		return -EOPNOTSUPP;

If we return 0 here, we can get rid of the

	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))

tests in all the drivers and let them call drm_gem_huge_mnt_create()
unconditionally.


> +
> +	type = get_fs_type("tmpfs");
> +	if (unlikely(!type))
> +		return -EOPNOTSUPP;
> +
> +	if (unlikely(dev->huge_mnt))
> +		return -EEXIST;
> +
> +	fc = fs_context_for_mount(type, SB_KERNMOUNT);
> +	if (IS_ERR(fc))
> +		return PTR_ERR(fc);
> +	ret = drm_gem_add_fc_param(fc, "source", "tmpfs");
> +	if (unlikely(ret))
> +		return -ENOPARAM;
> +	ret = drm_gem_add_fc_param(fc, "huge", value);
> +	if (unlikely(ret))
> +		return -ENOPARAM;
> +
> +	dev->huge_mnt = fc_mount_longterm(fc);
> +	put_fs_context(fc);
> +
> +	return drmm_add_action_or_reset(dev, drm_gem_huge_mnt_free, NULL);
> +}
> +EXPORT_SYMBOL_GPL(drm_gem_huge_mnt_create);
> +
>  static void
>  drm_gem_init_release(struct drm_device *dev, void *ptr)
>  {
> diff --git a/include/drm/drm_device.h b/include/drm/drm_device.h
> index 59fd3f4d5995..895b0ced972e 100644
> --- a/include/drm/drm_device.h
> +++ b/include/drm/drm_device.h
> @@ -3,6 +3,7 @@
>  
>  #include <linux/list.h>
>  #include <linux/kref.h>
> +#include <linux/mount.h>
>  #include <linux/mutex.h>
>  #include <linux/idr.h>
>  #include <linux/sched.h>
> @@ -168,6 +169,16 @@ struct drm_device {
>  	 */
>  	struct drm_master *master;
>  
> +	/**
> +	 * @huge_mnt:
> +	 *
> +	 * Huge tmpfs mountpoint used at GEM object initialization
> +	 * drm_gem_object_init(). Drivers can call drm_gem_huge_mnt_create() to
> +	 * create a huge tmfps mountpoint. The default tmpfs mountpoint
> +	 * (`shm_mnt`) is used if NULL.
> +	 */
> +	struct vfsmount *huge_mnt;
> +
>  	/**
>  	 * @driver_features: per-device driver features
>  	 *
> diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
> index 7c8bd67d087c..7285a62d9afc 100644
> --- a/include/drm/drm_gem.h
> +++ b/include/drm/drm_gem.h
> @@ -492,6 +492,7 @@ struct drm_gem_object {
>  		DRM_GEM_FOPS,\
>  	}
>  
> +int drm_gem_huge_mnt_create(struct drm_device *dev, const char *value);
>  void drm_gem_object_release(struct drm_gem_object *obj);
>  void drm_gem_object_free(struct kref *kref);
>  int drm_gem_object_init(struct drm_device *dev,

On Sat, Oct 04, 2025 at 11:30:46AM +0200, Loïc Molinari wrote:

> +static int drm_gem_add_fc_param(struct fs_context *fc, const char *key,
> +				const char *value)
> +{
> +	return vfs_parse_fs_string(fc, key, value, strlen(value));
> +}

Documentation/filesystems/porting.rst:
 
**mandatory**
  
Calling conventions for vfs_parse_fs_string() have changed; it does *not*
take length anymore (value ? strlen(value) : 0 is used).  If you want
a different length, use
   
	vfs_parse_fs_qstr(fc, key, &QSTR_LEN(value, len))
	    
instead.

IOW, your drm_gem_add_fc_param(fc, key, value) is an exact equivalent
of vfs_parse_fs_string(fc, key, value) now.