On 11/05/18 15:18, Chris Wilson wrote:
Quoting Lionel Landwerlin (2018-05-11 15:14:13)
My understanding of the virtual memory addressing from the GPU is limited...
But how can the GPU poke at the kernel's allocated data?
I thought we mapped into the GPU's address space only what is allocated
through gem.
Correct. The HW should only be accessing the pages through the GTT and
the GTT should only contain known pages (or a pointer to the scratch
page). There is maybe a hole where we are freeing the memory before
the HW has finished using it (still writing through stale TLB and
whatnot even though the system has reallocated the pages), but other
than that quite, quite scary. Hence this awooga.
-Chris
I managed to reproduce a kasan backtrace on the same test.
So it's not just the CI machine.
But I can't even startup a gdm on that machine with drm-tip. So maybe
there is some much more broken...
i915/perf unpins the object correctly before freeing (at which point it
could be reused).
Should we ensure i915_vma_destroy() i915/perf maybe?
It almost seems like this is an issue that could arise in other part of
the driver too.
-
Lionel
