On 2/17/2023 00:39, Hogander, Jouni wrote:
On Wed, 2023-02-15 at 17:10 -0800, John.C.Harrison@xxxxxxxxx wrote:
From: John Harrison <John.C.Harrison@xxxxxxxxx>
Instruction from hardware arch is that stolen memory and BAR mappings
are unsafe for use as ring buffers. There can be issues with cache
aliasing due to the CPU access going to memory via the BAR. So, don't
do it.
Tested these patches for GPU Hang I was debugging. Seem to fix that one
as well:
Tested-by: Jouni Högander <jouni.hogander@xxxxxxxxx>
Sweet! Out of interest, which platform was that? And how reproducible
was it? It would be interesting to know if an IGT was actually regularly
showing the issue and we had just been ignoring it!
John.
v2: Dont use BAR mappings either.
Make conditional on LLC so as not to change platforms that don't need
to change (Daniele).
Add 'Fixes' tags (Tvrtko).
v3: Fix dumb typo.
Signed-off-by: John Harrison <John.C.Harrison@xxxxxxxxx>
John Harrison (2):
drm/i915: Don't use stolen memory for ring buffers with LLC
drm/i915: Don't use BAR mappings for ring buffers with LLC
drivers/gpu/drm/i915/gt/intel_ring.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
