Re: [PATCH] drm/i915: Do not access stolen memory directly by the CPU, even for error capture

[Ben Widawsky <ben@bwidawsk.net>]

On Tue, Mar 04, 2014 at 03:45:56PM +0100, Daniel Vetter wrote:
> On Tue, Feb 18, 2014 at 11:18:04AM -0800, Ben Widawsky wrote:
> > On Wed, Feb 12, 2014 at 07:18:40PM +0000, Chris Wilson wrote:
> > > For stolen pages, since it is verboten to access them directly on many
> > > architectures, we have to read them through the GTT aperture. If they
> > > are not accessible through the aperture, then we have to abort.
> > > 
> > > This was complicated by
> > > 
> > > commit 8b6124a633d8095b0c8364f585edff9c59568a96
> > > Author: Chris Wilson <chris@chris-wilson.co.uk>
> > > Date:   Thu Jan 30 14:38:16 2014 +0000
> > > 
> > >     drm/i915: Don't access snooped pages through the GTT (even for error capture)
> > > 
> > > and the desire to use stolen memory for ringbuffers, contexts and
> > > batches in the future.
> > > 
> > > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > 
> > I'd prefer separate functions for the different types of error objects
> > (gtt vs CPU mapped). Or maybe just pass in the capture type as an
> > argument and then create a helper to determine the right thing. It'd at
> > least be a bit easier for review.
> > 
> > Anyway, having not actually looked at the code, the idea is solid:
> > Acked-by: Ben Widawsky <ben@bwidawsk.net>
> 
> Can you please actually look at the code and upgrade this to a full
> review?
> 
> Thanks, Daniel

I had been hoping for a bit of a rewrite to do the review. Chris are you
opposed to my suggestions?

> > 
> > > ---
> > >  drivers/gpu/drm/i915/i915_gpu_error.c | 50 ++++++++++++++++++++++-------------
> > >  1 file changed, 31 insertions(+), 19 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
> > > index 0e1f7b691082..a2c3a639c3cc 100644
> > > --- a/drivers/gpu/drm/i915/i915_gpu_error.c
> > > +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
> > > @@ -542,10 +542,11 @@ static struct drm_i915_error_object *
> > >  i915_error_object_create_sized(struct drm_i915_private *dev_priv,
> > >  			       struct drm_i915_gem_object *src,
> > >  			       struct i915_address_space *vm,
> > > -			       const int num_pages)
> > > +			       int num_pages)
> > >  {
> > >  	struct drm_i915_error_object *dst;
> > > -	int i;
> > > +	bool use_ggtt;
> > > +	int i = 0;
> > >  	u32 reloc_offset;
> > >  
> > >  	if (src == NULL || src->pages == NULL)
> > > @@ -555,8 +556,32 @@ i915_error_object_create_sized(struct drm_i915_private *dev_priv,
> > >  	if (dst == NULL)
> > >  		return NULL;
> > >  
> > > -	reloc_offset = dst->gtt_offset = i915_gem_obj_offset(src, vm);
> > > -	for (i = 0; i < num_pages; i++) {
> > > +	dst->gtt_offset = i915_gem_obj_offset(src, vm);
> > > +
> > > +	reloc_offset = dst->gtt_offset;
> > > +	use_ggtt = (src->cache_level == I915_CACHE_NONE &&
> > > +		    i915_is_ggtt(vm) &&
> > > +		    src->has_global_gtt_mapping &&
> > > +		    reloc_offset + num_pages * PAGE_SIZE <= dev_priv->gtt.mappable_end);
> > > +
> > > +	/* Cannot access stolen address directly, try to use the aperture */
> > > +	if (src->stolen) {
> > > +		use_ggtt = true;
> > > +
> > > +		if (!src->has_global_gtt_mapping)
> > > +			goto unwind;
> > > +
> > > +		reloc_offset = i915_gem_obj_ggtt_offset(src);
> > > +		if (reloc_offset + num_pages * PAGE_SIZE > dev_priv->gtt.mappable_end)
> > > +			goto unwind;
> > > +	}
> > > +
> > > +	/* Cannot access snooped pages through the aperture */
> > > +	if (use_ggtt && src->cache_level != I915_CACHE_NONE && !HAS_LLC(dev_priv->dev))
> > > +		goto unwind;
> > > +
> > > +	dst->page_count = num_pages;
> > > +	while (num_pages--) {
> > >  		unsigned long flags;
> > >  		void *d;
> > >  
> > > @@ -565,10 +590,7 @@ i915_error_object_create_sized(struct drm_i915_private *dev_priv,
> > >  			goto unwind;
> > >  
> > >  		local_irq_save(flags);
> > > -		if (src->cache_level == I915_CACHE_NONE &&
> > > -		    reloc_offset < dev_priv->gtt.mappable_end &&
> > > -		    src->has_global_gtt_mapping &&
> > > -		    i915_is_ggtt(vm)) {
> > > +		if (use_ggtt) {
> > >  			void __iomem *s;
> > >  
> > >  			/* Simply ignore tiling or any overlapping fence.
> > > @@ -580,14 +602,6 @@ i915_error_object_create_sized(struct drm_i915_private *dev_priv,
> > >  						     reloc_offset);
> > >  			memcpy_fromio(d, s, PAGE_SIZE);
> > >  			io_mapping_unmap_atomic(s);
> > > -		} else if (src->stolen) {
> > > -			unsigned long offset;
> > > -
> > > -			offset = dev_priv->mm.stolen_base;
> > > -			offset += src->stolen->start;
> > > -			offset += i << PAGE_SHIFT;
> > > -
> > > -			memcpy_fromio(d, (void __iomem *) offset, PAGE_SIZE);
> > >  		} else {
> > >  			struct page *page;
> > >  			void *s;
> > > @@ -604,11 +618,9 @@ i915_error_object_create_sized(struct drm_i915_private *dev_priv,
> > >  		}
> > >  		local_irq_restore(flags);
> > >  
> > > -		dst->pages[i] = d;
> > > -
> > > +		dst->pages[i++] = d;
> > >  		reloc_offset += PAGE_SIZE;
> > >  	}
> > > -	dst->page_count = num_pages;
> > >  
> > >  	return dst;
> > >  
> > > -- 
> > > 1.9.0.rc3
> > > 
> > > _______________________________________________
> > > Intel-gfx mailing list
> > > Intel-gfx@lists.freedesktop.org
> > > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> > 
> > -- 
> > Ben Widawsky, Intel Open Source Technology Center
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx@lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch

-- 
Ben Widawsky, Intel Open Source Technology Center