Re: [PATCH v2 1/2] drm/panthor: Treat a zero-length VM_BIND op as a no-op

[Liviu Dudau <liviu.dudau@arm.com>]

On Wed, Sep 02, 2026 at 08:28:42PM +0800, Zhenhao Wan wrote:
> panthor_vm_bind_exec_sync_op() short-circuits a zero-length operation: it
> returns 0 immediately when op->size is 0. The asynchronous VM_BIND path
> has no equivalent guard.
> 
> An async MAP or UNMAP with size == 0 is not rejected: only alignment is
> checked in panthor_vm_bind_prepare_op_ctx() and IS_ALIGNED(0) is true, so
> the op is queued and panthor_vm_exec_op() calls drm_gpuvm_sm_map() /
> drm_gpuvm_sm_unmap() with a zero range. A zero-length map into unmapped
> space then reaches drm_gpuva_insert(), where the GPUVA interval-tree last
> key addr + range - 1 underflows to addr - 1 and a malformed node whose end
> lies below its start can be inserted, corrupting the augmented interval
> tree.
> 
> Mirror the synchronous path and treat a zero-length map or unmap as a no-op
> in panthor_vm_exec_op(), before any lock is taken or the GPUVA tree is
> touched. This also keeps the async path robust if the core drm_gpuvm range
> validation is tightened to reject a zero range, which would otherwise make
> panthor_vm_bind_run_job() flag the VM unusable on the resulting -EINVAL.
> 
> Fixes: 647810ec2476 ("drm/panthor: Add the MMU/VM logical block")
> Reported-by: Yuhao Jiang <danisjiang@gmail.com>
> Assisted-by: Claude:claude-opus-5
> Cc: stable@vger.kernel.org
> Signed-off-by: Zhenhao Wan <whi4ed0g@gmail.com>

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

Best regards,
Liviu

> ---
>  drivers/gpu/drm/panthor/panthor_mmu.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> index e592a8ebb478..93542f59cb5e 100644
> --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> @@ -2591,6 +2591,15 @@ panthor_vm_exec_op(struct panthor_vm *vm, struct panthor_vm_op_ctx *op,
>  	if (op_type == DRM_PANTHOR_VM_BIND_OP_TYPE_SYNC_ONLY)
>  		return 0;
>  
> +	/*
> +	 * A zero-length map or unmap is a no-op. The synchronous bind path
> +	 * already short-circuits it in panthor_vm_bind_exec_sync_op(); mirror
> +	 * that here so an asynchronous zero-length op does not fail and flag the
> +	 * VM as unusable.
> +	 */
> +	if (!op->va.range)
> +		return 0;
> +
>  	mutex_lock(&vm->op_lock);
>  	vm->op_ctx = op;
>  
> 
> -- 
> 2.34.1
> 

-- 
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