[PATCH v3 2/2] drm/i915/gvt: Fix inconsistent locks holding sequence

[Chuanxiao Dong]

There are two kinds of locking sequence.

One is in the thread which is started by vfio ioctl to do
the iommu unmapping. The locking sequence is:
	down_read(&group_lock) ----> mutex_lock(&cached_lock)

The other is in the vfio release thread which will unpin all
the cached pages. The lock sequence is:
	mutex_lock(&cached_lock) ---> down_read(&group_lock)

And, the cache_lock is used to protect the rb tree of the cache
node and doing vfio unpin doesn't require this lock. Move the
vfio unpin out of the cache_lock protected region.

v2:
- use for style instead of do{}while(1). (Zhenyu)

Fixes: f30437c5e7bf ("drm/i915/gvt: add KVMGT support")
Signed-off-by: Chuanxiao Dong <chuanxiao.dong at intel.com>
Cc: Zhenyu Wang <zhenyuw at linux.intel.com>
Cc: stable at vger.kernel.org # v4.10+
---
 drivers/gpu/drm/i915/gvt/kvmgt.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
index 56a8d6a..75a6e1d 100644
--- a/drivers/gpu/drm/i915/gvt/kvmgt.c
+++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
@@ -260,16 +260,20 @@ static void gvt_cache_destroy(struct intel_vgpu *vgpu)
 	struct device *dev = mdev_dev(vgpu->vdev.mdev);
 	unsigned long gfn;
 
-	mutex_lock(&vgpu->vdev.cache_lock);
-	while ((node = rb_first(&vgpu->vdev.cache))) {
+	for (;;) {
+		mutex_lock(&vgpu->vdev.cache_lock);
+		node = rb_first(&vgpu->vdev.cache);
+		if (!node) {
+			mutex_unlock(&vgpu->vdev.cache_lock);
+			break;
+		}
 		dma = rb_entry(node, struct gvt_dma, node);
 		gvt_dma_unmap_iova(vgpu, dma->iova);
 		gfn = dma->gfn;
-
-		vfio_unpin_pages(dev, &gfn, 1);
 		__gvt_cache_remove_entry(vgpu, dma);
+		mutex_unlock(&vgpu->vdev.cache_lock);
+		vfio_unpin_pages(dev, &gfn, 1);
 	}
-	mutex_unlock(&vgpu->vdev.cache_lock);
 }
 
 static struct intel_vgpu_type *intel_gvt_find_vgpu_type(struct intel_gvt *gvt,
-- 
2.7.4