[PATCH v3 4/5] drm/panthor: Fix an off-by-one in the heap context retrieval logic

[Steven Price]

On 02/05/2024 16:40, Boris Brezillon wrote:
> The heap ID is used to index the heap context pool, and allocating
> in the [1:MAX_HEAPS_PER_POOL] leads to an off-by-one. This was
> originally to avoid returning a zero heap handle, but given the handle
> is formed with (vm_id << 16) | heap_id, with vm_id > 0, we already can't
> end up with a valid heap handle that's zero.
> 
> v3:
> - Allocate in the [0:MAX_HEAPS_PER_POOL-1] range
> 
> v2:
> - New patch
> 
> Fixes: 9cca48fa4f89 ("drm/panthor: Add the heap logical block")
> Reported-by: Eric Smith <eric.smith at collabora.com>
> Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>
> Tested-by: Eric Smith <eric.smith at collabora.com>

Don't we also need to change the xa_init_flags() in
panthor_heap_pool_create()?

Steve

> ---
>  drivers/gpu/drm/panthor/panthor_heap.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_heap.c b/drivers/gpu/drm/panthor/panthor_heap.c
> index 683bb94761bc..252332f5390f 100644
> --- a/drivers/gpu/drm/panthor/panthor_heap.c
> +++ b/drivers/gpu/drm/panthor/panthor_heap.c
> @@ -323,7 +323,8 @@ int panthor_heap_create(struct panthor_heap_pool *pool,
>  	if (!pool->vm) {
>  		ret = -EINVAL;
>  	} else {
> -		ret = xa_alloc(&pool->xa, &id, heap, XA_LIMIT(1, MAX_HEAPS_PER_POOL), GFP_KERNEL);
> +		ret = xa_alloc(&pool->xa, &id, heap,
> +			       XA_LIMIT(0, MAX_HEAPS_PER_POOL - 1), GFP_KERNEL);
>  		if (!ret) {
>  			void *gpu_ctx = panthor_get_heap_ctx(pool, id);
>