Re: [PATCH] drm/panthor: Fix handling of partial GPU mapping of BOs

[Steven Price <steven.price@arm.com>]

On 11/11/2024 09:26, Akash Goel wrote:
> This commit fixes the handling of partial GPU mapping of buffer objects
> in Panthor.
> VM_BIND ioctl allows Userspace to partially map the BOs to GPU.
> To map a BO, Panthor walks through the sg_table to retrieve the physical
> address of pages. If the mapping is created at an offset into the BO,
> then the scatterlist(s) at the beginning have to be skipped to reach the
> one corresponding to the offset. But the case where the offset didn't
> point to the first page of desired scatterlist wasn't handled correctly.
> The bug caused the partial GPU mapping of BO to go wrong for the said
> case, as the pages didn't get map at the expected virtual address and
> consequently there were kernel warnings on unmap.
> 
> Signed-off-by: Akash Goel <akash.goel@arm.com>

Fixes: 647810ec2476 ("drm/panthor: Add the MMU/VM logical block")

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

Thanks,
Steve

> ---
>  drivers/gpu/drm/panthor/panthor_mmu.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> index d8cc9e7d064e..6bc188d9a9ad 100644
> --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> @@ -957,6 +957,7 @@ panthor_vm_map_pages(struct panthor_vm *vm, u64 iova, int prot,
>  
>  		paddr += offset;
>  		len -= offset;
> +		offset = 0;
>  		len = min_t(size_t, len, size);
>  		size -= len;
>