Re: [PATCH 2/2] drm/i915: Don't access snooped pages through the GTT (even for error capture)

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Jan 30, 2014 at 02:38:16PM +0000, Chris Wilson wrote:
> We want to use the GTT for reading back objects upon an error so that we
> have exactly the information that the GPU saw. However, it is verboten
> to access snoopable pages through the GTT and causes my PineView GPU to
> throw a page fault instead.
> 
> This has not been a problem in the past as we only dumped ringbuffers
> and batchbuffers, both of which must be uncached. However, the
> introduction of HWS page dumping leads to a read of a snooped object
> through the GTT. This was introduced by
> 
> commit f3ce3821393e31a3f1a8ca6c24eb2d735a428445
> Author: Chris Wilson <chris@chris-wilson.co.uk>
> Date:   Thu Jan 23 22:40:36 2014 +0000
> 
>     drm/i915: Include HW status page in error capture
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_gpu_error.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
> index 6d5ab945132c..3b18c2dff3b8 100644
> --- a/drivers/gpu/drm/i915/i915_gpu_error.c
> +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
> @@ -527,7 +527,8 @@ i915_error_object_create_sized(struct drm_i915_private *dev_priv,
>  			goto unwind;
>  
>  		local_irq_save(flags);
> -		if (reloc_offset < dev_priv->gtt.mappable_end &&
> +		if (src->cache_level == I915_CACHE_NONE &&
> +		    reloc_offset < dev_priv->gtt.mappable_end &&
>  		    src->has_global_gtt_mapping &&
>  		    i915_is_ggtt(vm)) {
>  			void __iomem *s;

So you don't want to make it (cache_level == NONE || HAS_LLC)?

-- 
Ville Syrjälä
Intel OTC