[Mesa-stable] [Mesa-dev] [PATCH] i965: Fix buffer overruns in MSAA MCS buffer clearing.

[Kenneth Graunke]

On 04/15/2014 10:08 AM, Mike Stroyan wrote:
> I would go farther than requiring the returned bo->size to be covered by
> backing pages.
> There really should be backing pages for every page mapped by
> drm_intel_gem_bo_map.
> No mapped addresses should be affecting memory outside of an object's
> backing pages.
> 
> If tiling can result in access to unallocated memory it might even lead
> to corruption of data in pages
> used by different processes.  That would break GL_ARB_robustness
> requirements.

It shouldn't, now that proper PPGTT support has landed in the kernel -
only data belonging to a single process is mapped into its address
space.  So, a process can accidentally read or trash other portions of
its own memory, but never any other memory.  This seems acceptable, as
it's how things work with normal CPU programs.

That said, with older kernels, where we had only Global GTT or the
aliasing PPGTT (using the PPGTT mechanism but storing the exact same
mappings at the GGTT), you could definitely see/stomp other people's
memory.  Which is awful, and one reason we think PPGTT support is so
important.

--Ken

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