Re: [PATCH v4 13/18] drm/panthor: Complain if the SOFT_RESET fails

[Adrian Larumbe <adrian.larumbe@collabora.com>]

On 26.08.2026 16:56, Boris Brezillon wrote:
> We rely on a functioning SOFT_RESET to avoid HW UAFs when the GPU was
> in a state where AS commands were no longer accepted. If we silently
> ignore RESET failures, we're just pretending to be safe while exposing
> ourselves to the very UAFs we were trying to avoid. On the other hand,
> there's basically nothing we can do if both the SOFT_RESET and the
> AS_COMMAND(UNMAPPED) fail, so do what we do best: complain loudly and
> taint the kernel with a WARN_ON().
> 
> Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
> ---
>  drivers/gpu/drm/panthor/panthor_hw.h | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_hw.h b/drivers/gpu/drm/panthor/panthor_hw.h
> index 4531c1239cb6..f13fd7b335c1 100644
> --- a/drivers/gpu/drm/panthor/panthor_hw.h
> +++ b/drivers/gpu/drm/panthor/panthor_hw.h
> @@ -41,9 +41,17 @@ int panthor_hw_init(struct panthor_device *ptdev);
>  int panthor_hw_power_status_register(void);
>  void panthor_hw_power_status_unregister(void);
>  
> -static inline int panthor_hw_soft_reset(struct panthor_device *ptdev)
> +static inline void
> +panthor_hw_soft_reset(struct panthor_device *ptdev)
>  {
> -	return ptdev->hw->ops.soft_reset(ptdev);
> +	/* We're relying on the SOFT_RESET to reset the MMU block if some AS
> +	 * were stuck for some reason. Failing to reset the MMU/L2 means we're
> +	 * exposing ourselves to HW UAFs. On the other hand, there's basically
> +	 * nothing we can do if both the SOFT_RESET and
> +	 * the AS_COMMAND(UNMAPPED) fail, so do what we do best: complain loudly
> +	 * and taint the kernel.
> +	 */
> +	drm_WARN_ON(&ptdev->base, ptdev->hw->ops.soft_reset(ptdev));

I think you forgot to include drm/drm_print.h, although Sashiko probably picked up on this.

On top of that, I wonder if failure to soft reset should be carried up the call stack and
eventually lead to an early unplug, just like you do when panthor_fw_post_reset() fails.

>  }
>  
>  static inline int panthor_hw_l2_power_on(struct panthor_device *ptdev)
> 
> -- 
> 2.55.0


Adrian Larumbe