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[PATCH 4.19 002/101] 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@xxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx #4.14+
Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
Signed-off-by: Zhenyu Wang <zhenyuw@xxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
 drivers/gpu/drm/i915/gvt/gtt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
index 00aad8164dec..542f31ce108f 100644
--- a/drivers/gpu/drm/i915/gvt/gtt.c
+++ b/drivers/gpu/drm/i915/gvt/gtt.c
@@ -1940,7 +1940,7 @@ 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);