[PATCH] nouveau/fence: handle cross device fences properly.

[Dave Airlie]

From: Dave Airlie <airlied at redhat.com>

If we have two nouveau controlled devices and one passes a dma-fence
to the other, when we hit the sync path it can cause the second device
to try and put a sync wait in it's pushbuf for the seqno of the context
on the first device.

Since fence contexts are vmm bound, check the if vmm's match between
both users, this should ensure that fence seqnos don't get used wrongly
on incorrect channels.

This seems to happen fairly spuriously and I found it tracking down
a multi-card regression report, that seems to work by luck before this.

Signed-off-by: Dave Airlie <airlied at redhat.com>
Cc: stable at vger.kernel.org
---
 drivers/gpu/drm/nouveau/nouveau_fence.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c b/drivers/gpu/drm/nouveau/nouveau_fence.c
index ee5e9d40c166f..5743c82f4094b 100644
--- a/drivers/gpu/drm/nouveau/nouveau_fence.c
+++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
@@ -370,7 +370,8 @@ nouveau_fence_sync(struct nouveau_bo *nvbo, struct nouveau_channel *chan,
 
 				rcu_read_lock();
 				prev = rcu_dereference(f->channel);
-				if (prev && (prev == chan ||
+				if (prev && (prev->vmm == chan->vmm) &&
+				    (prev == chan ||
 					     fctx->sync(f, prev, chan) == 0))
 					must_wait = false;
 				rcu_read_unlock();
-- 
2.43.0