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

[Boris Brezillon <boris.brezillon@collabora.com>]

On Thu, 2 May 2024 16:52:24 +0100
Steven Price <steven.price@arm.com> wrote:

> 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@collabora.com>
> > Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
> > Tested-by: Eric Smith <eric.smith@collabora.com>  
> 
> Don't we also need to change the xa_init_flags() in
> panthor_heap_pool_create()?

Uh, we should, indeed.

> 
> 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);
> >    
>