[Intel-gfx] [PATCH] drm/i915/gt: Prevent use of engine->wa_ctx after error

[Matt Roper]

On Fri, Jan 08, 2021 at 03:09:24PM +0000, Chris Wilson wrote:
> On error we unpin and free the wa_ctx.vma, but do not clear any of the
> derived flags. During lrc_init, we look at the flags and attempt to
> dereference the wa_ctx.vma if they are set. To protect the error path
> where we try to limp along without the wa_ctx, make sure we clear those
> flags!
> 
> Reported-by: Matt Roper <matthew.d.roper at intel.com>
> Fixes: 604a8f6f1e33 ("drm/i915/lrc: Only enable per-context and per-bb buffers if set")
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Matt Roper <matthew.d.roper at intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> Cc: <stable at vger.kernel.org> # v4.15+

Reviewed-by: Matt Roper <matthew.d.roper at intel.com>

> ---
>  drivers/gpu/drm/i915/gt/intel_lrc.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index 4e856947fb13..703d9ecc3f7e 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -1453,6 +1453,9 @@ static int lrc_setup_wa_ctx(struct intel_engine_cs *engine)
>  void lrc_fini_wa_ctx(struct intel_engine_cs *engine)
>  {
>  	i915_vma_unpin_and_release(&engine->wa_ctx.vma, 0);
> +
> +	/* Called on error unwind, clear all flags to prevent further use */
> +	memset(&engine->wa_ctx, 0, sizeof(engine->wa_ctx));
>  }
>  
>  typedef u32 *(*wa_bb_func_t)(struct intel_engine_cs *engine, u32 *batch);
> -- 
> 2.20.1
> 

-- 
Matt Roper
Graphics Software Engineer
VTT-OSGC Platform Enablement
Intel Corporation
(916) 356-2795