[PATCH v2 1/2] drm/panthor: Extend VM locked region for remap case to be a superset

[PATCH v2 1/2] drm/panthor: Extend VM locked region for remap case to be a superset

[Adrián Larumbe]

In the event of an sm_step_remap() that leads to a partial unmap of a
transparent huge page, the new locked region required by an extended unmap
might not be a superset of the original one. Then, if it leaves a portion
of the initially requested one out, the ensuing map will trigger a warning.

Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
Fixes: 8e7460eac786 ("drm/panthor: Support partial unmaps of huge pages")
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
---
 drivers/gpu/drm/panthor/panthor_mmu.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
index fa8b31df85c9..bd41c892beb7 100644
--- a/drivers/gpu/drm/panthor/panthor_mmu.c
+++ b/drivers/gpu/drm/panthor/panthor_mmu.c
@@ -1709,6 +1709,25 @@ static int panthor_vm_lock_region(struct panthor_vm *vm, u64 start, u64 size)
 	    start + size <= vm->locked_region.start + vm->locked_region.size)
 		return 0;
 
+	/* sm_step_remap() may need a locked region that isn't a strict superset
+	 * of the original one because of having to extend unmap boundaries beyond
+	 * it to deal with partial unmaps of transparent huge pages. What we want
+	 * in those cases is to lock the union of both regions. The new region must
+	 * always overlap with the original one, because the upper and lower unmap
+	 * boundaries in a remap operation can only shift up or down respectively,
+	 * but never otherwise.
+	 */
+	if (vm->locked_region.size) {
+		u64 end = max(vm->locked_region.start + vm->locked_region.size,
+			      start + size);
+
+		drm_WARN_ON_ONCE(&vm->ptdev->base, (start + size <= vm->locked_region.start) ||
+				 (start >= vm->locked_region.start + vm->locked_region.size));
+
+		start = min(start, vm->locked_region.start);
+		size = end - start;
+	}
+
 	mutex_lock(&ptdev->mmu->as.slots_lock);
 	if (vm->as.id >= 0 && size) {
 		/* Lock the region that needs to be updated */
-- 
2.53.0

[PATCH v2 2/2] drm/panthor: Fix outdated function documentation

[Adrián Larumbe]

'vm' is no longer allowed to be NULL.

Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
---
 drivers/gpu/drm/panthor/panthor_gem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
index 69cef05b6ef7..13295d7a593d 100644
--- a/drivers/gpu/drm/panthor/panthor_gem.c
+++ b/drivers/gpu/drm/panthor/panthor_gem.c
@@ -1264,7 +1264,7 @@ void panthor_kernel_bo_destroy(struct panthor_kernel_bo *bo)
 /**
  * panthor_kernel_bo_create() - Create and map a GEM object to a VM
  * @ptdev: Device.
- * @vm: VM to map the GEM to. If NULL, the kernel object is not GPU mapped.
+ * @vm: VM to map the GEM to.
  * @size: Size of the buffer object.
  * @bo_flags: Combination of drm_panthor_bo_flags flags.
  * @vm_map_flags: Combination of drm_panthor_vm_bind_op_flags (only those
-- 
2.53.0

Re: [PATCH v2 1/2] drm/panthor: Extend VM locked region for remap case to be a superset

[Liviu Dudau]

On Wed, Apr 08, 2026 at 08:12:23PM +0100, Adrián Larumbe wrote:
> In the event of an sm_step_remap() that leads to a partial unmap of a
> transparent huge page, the new locked region required by an extended unmap
> might not be a superset of the original one. Then, if it leaves a portion
> of the initially requested one out, the ensuing map will trigger a warning.
> 
> Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
> Fixes: 8e7460eac786 ("drm/panthor: Support partial unmaps of huge pages")
> Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>

Best regards,
Liviu

> ---
>  drivers/gpu/drm/panthor/panthor_mmu.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> index fa8b31df85c9..bd41c892beb7 100644
> --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> @@ -1709,6 +1709,25 @@ static int panthor_vm_lock_region(struct panthor_vm *vm, u64 start, u64 size)
>  	    start + size <= vm->locked_region.start + vm->locked_region.size)
>  		return 0;
>  
> +	/* sm_step_remap() may need a locked region that isn't a strict superset
> +	 * of the original one because of having to extend unmap boundaries beyond
> +	 * it to deal with partial unmaps of transparent huge pages. What we want
> +	 * in those cases is to lock the union of both regions. The new region must
> +	 * always overlap with the original one, because the upper and lower unmap
> +	 * boundaries in a remap operation can only shift up or down respectively,
> +	 * but never otherwise.
> +	 */
> +	if (vm->locked_region.size) {
> +		u64 end = max(vm->locked_region.start + vm->locked_region.size,
> +			      start + size);
> +
> +		drm_WARN_ON_ONCE(&vm->ptdev->base, (start + size <= vm->locked_region.start) ||
> +				 (start >= vm->locked_region.start + vm->locked_region.size));
> +
> +		start = min(start, vm->locked_region.start);
> +		size = end - start;
> +	}
> +
>  	mutex_lock(&ptdev->mmu->as.slots_lock);
>  	if (vm->as.id >= 0 && size) {
>  		/* Lock the region that needs to be updated */
> -- 
> 2.53.0
> 

-- 
====================
| I would like to |
| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
  ---------------
    ¯\_(ツ)_/¯

Re: [PATCH v2 2/2] drm/panthor: Fix outdated function documentation

[Liviu Dudau]

On Wed, Apr 08, 2026 at 08:12:24PM +0100, Adrián Larumbe wrote:
> 'vm' is no longer allowed to be NULL.
> 
> Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
> Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>

Best regards,
Liviu

> ---
>  drivers/gpu/drm/panthor/panthor_gem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
> index 69cef05b6ef7..13295d7a593d 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.c
> +++ b/drivers/gpu/drm/panthor/panthor_gem.c
> @@ -1264,7 +1264,7 @@ void panthor_kernel_bo_destroy(struct panthor_kernel_bo *bo)
>  /**
>   * panthor_kernel_bo_create() - Create and map a GEM object to a VM
>   * @ptdev: Device.
> - * @vm: VM to map the GEM to. If NULL, the kernel object is not GPU mapped.
> + * @vm: VM to map the GEM to.
>   * @size: Size of the buffer object.
>   * @bo_flags: Combination of drm_panthor_bo_flags flags.
>   * @vm_map_flags: Combination of drm_panthor_vm_bind_op_flags (only those
> -- 
> 2.53.0
> 

-- 
====================
| I would like to |
| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
  ---------------
    ¯\_(ツ)_/¯

Re: [PATCH v2 1/2] drm/panthor: Extend VM locked region for remap case to be a superset

[Steven Price]

On 08/04/2026 20:12, Adrián Larumbe wrote:
> In the event of an sm_step_remap() that leads to a partial unmap of a
> transparent huge page, the new locked region required by an extended unmap
> might not be a superset of the original one. Then, if it leaves a portion
> of the initially requested one out, the ensuing map will trigger a warning.
> 
> Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
> Fixes: 8e7460eac786 ("drm/panthor: Support partial unmaps of huge pages")
> Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

Reviewed-by: Steven Price <steven.price@arm.com>

Although I'm starting to wonder if we should split this into an "initial
lock" and an "expand lock" function. Still as a minimal fix this is good.

Thanks,
Steve

> ---
>  drivers/gpu/drm/panthor/panthor_mmu.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> index fa8b31df85c9..bd41c892beb7 100644
> --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> @@ -1709,6 +1709,25 @@ static int panthor_vm_lock_region(struct panthor_vm *vm, u64 start, u64 size)
>  	    start + size <= vm->locked_region.start + vm->locked_region.size)
>  		return 0;
>  
> +	/* sm_step_remap() may need a locked region that isn't a strict superset
> +	 * of the original one because of having to extend unmap boundaries beyond
> +	 * it to deal with partial unmaps of transparent huge pages. What we want
> +	 * in those cases is to lock the union of both regions. The new region must
> +	 * always overlap with the original one, because the upper and lower unmap
> +	 * boundaries in a remap operation can only shift up or down respectively,
> +	 * but never otherwise.
> +	 */
> +	if (vm->locked_region.size) {
> +		u64 end = max(vm->locked_region.start + vm->locked_region.size,
> +			      start + size);
> +
> +		drm_WARN_ON_ONCE(&vm->ptdev->base, (start + size <= vm->locked_region.start) ||
> +				 (start >= vm->locked_region.start + vm->locked_region.size));
> +
> +		start = min(start, vm->locked_region.start);
> +		size = end - start;
> +	}
> +
>  	mutex_lock(&ptdev->mmu->as.slots_lock);
>  	if (vm->as.id >= 0 && size) {
>  		/* Lock the region that needs to be updated */

Re: [PATCH v2 2/2] drm/panthor: Fix outdated function documentation

[Steven Price]

On 08/04/2026 20:12, Adrián Larumbe wrote:
> 'vm' is no longer allowed to be NULL.
> 
> Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
> Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

Reviewed-by: Steven Price <steven.price@arm.com>

And for completeness:

Fixes: 8a1cc07578bf ("drm/panthor: Add GEM logical block")

Thanks,

Steve

> ---
>  drivers/gpu/drm/panthor/panthor_gem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
> index 69cef05b6ef7..13295d7a593d 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.c
> +++ b/drivers/gpu/drm/panthor/panthor_gem.c
> @@ -1264,7 +1264,7 @@ void panthor_kernel_bo_destroy(struct panthor_kernel_bo *bo)
>  /**
>   * panthor_kernel_bo_create() - Create and map a GEM object to a VM
>   * @ptdev: Device.
> - * @vm: VM to map the GEM to. If NULL, the kernel object is not GPU mapped.
> + * @vm: VM to map the GEM to.
>   * @size: Size of the buffer object.
>   * @bo_flags: Combination of drm_panthor_bo_flags flags.
>   * @vm_map_flags: Combination of drm_panthor_vm_bind_op_flags (only those