Re: [PATCH] drm/i915: Only fence tiled region of object.

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

On Thu, Dec 18, 2014 at 09:37:37PM +0100, Daniel Vetter wrote:
> On Thu, Dec 18, 2014 at 09:51:26AM -0800, Bob Paauwe wrote:
> > When creating a fence for a tiled object, only fence the area that
> > makes up the actual tiles.  The object may be larger than the tiled
> > area and if we allow those extra addresses to be fenced, they'll
> > get converted to addresses beyond where the object is mapped. This
> > opens up the possiblity of writes beyond the end of object.
> > 
> > To prevent this, we adjust the size of the fence to only encompass
> > the area that makes up the actual tiles.  The extra space is considered
> > un-tiled and now behaves as if it was a linear object.
> > 
> > Testcase: igt/gem_tiled_fence_overflow
> > Reported-by: Dan Hettena <danh@ghs.com>
> > Signed-off-by: Bob Paauwe <bob.j.paauwe@intel.com>
> 
> Presuming this indeed blows up (I didn't try your test) this is one for
> Jani.

Hmm. Wasn't this problem discussed a few years ago already? My recollection
is that Imre had patches but you said you don't care about the problem.

> 
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: stable@vger.kernel.org
> 
> Thanks, Daniel
> 
> > ---
> >  drivers/gpu/drm/i915/i915_gem.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> > index 67550ac..c9acbfa 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -3173,6 +3173,13 @@ static void i965_write_fence_reg(struct drm_device *dev, int reg,
> >  		u32 size = i915_gem_obj_ggtt_size(obj);
> >  		uint64_t val;
> >  
> > +		/* Adjust fence size to match tiled area */
> > +		if (obj->tiling_mode != I915_TILING_NONE) {
> > +			uint32_t row_size = obj->stride *
> > +				(obj->tiling_mode == I915_TILING_Y ? 32 : 8);
> > +			size = (size / row_size) * row_size;
> > +		}
> > +
> >  		val = (uint64_t)((i915_gem_obj_ggtt_offset(obj) + size - 4096) &
> >  				 0xfffff000) << 32;
> >  		val |= i915_gem_obj_ggtt_offset(obj) & 0xfffff000;
> > -- 
> > 2.1.0
> > 
> > _______________________________________________
> > 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
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Ville Syrjälä
Intel OTC
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