drm/i915/gvt: do not let pin count of shadow mm go negative

[ Upstream commit 663a50ceac75c2208d2ad95365bc8382fd42f44d ]

shadow mm's pin count got increased in workload preparation phase, which
is after workload scanning.
it will get decreased in complete_current_workload() anyway after
workload completion.
Sometimes, if a workload meets a scanning error, its shadow mm pin count
will not get increased but will get decreased in the end.
This patch lets shadow mm's pin count not go below 0.

Fixes: 2707e4446688 ("drm/i915/gvt: vGPU graphics memory virtualization")
Cc: zhenyuw@linux.intel.com
Cc: stable@vger.kernel.org #4.14+
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
index c7103dd2d8d571fde462f173dcc67efc0973cc69..563ab8590061d99f0839d130df8a491eff677f5c 100644 (file)
--- a/drivers/gpu/drm/i915/gvt/gtt.c
+++ b/drivers/gpu/drm/i915/gvt/gtt.c
@@ -1942,7 +1942,7 @@ void _intel_vgpu_mm_release(struct kref *mm_ref)
  */
 void intel_vgpu_unpin_mm(struct intel_vgpu_mm *mm)
 {
-       atomic_dec(&mm->pincount);
+       atomic_dec_if_positive(&mm->pincount);
 }
 
 /**