iommu/vt-d: Fix mm reference leak

Move canonical address check before mmget_not_zero() to avoid mm
reference leak.

Fixes: 9d8c3af ("iommu/vt-d: IOMMU Page Request needs to check if address is canonical.")
Signed-off-by: Jacob Pan <[email protected]>
Acked-by: Lu Baolu <[email protected]>
Signed-off-by: Joerg Roedel <[email protected]>

Author: Jacob Pan

drivers/iommu/intel-svm.c

@@ -611,14 +611,15 @@ static irqreturn_t prq_event_thread(int irq, void *d)
 		 * any faults on kernel addresses. */
 		if (!svm->mm)
 			goto bad_req;
-		/* If the mm is already defunct, don't handle faults. */
-		if (!mmget_not_zero(svm->mm))
-			goto bad_req;
 
 		/* If address is not canonical, return invalid response */
 		if (!is_canonical_address(address))
 			goto bad_req;
 
+		/* If the mm is already defunct, don't handle faults. */
+		if (!mmget_not_zero(svm->mm))
+			goto bad_req;
+
 		down_read(&svm->mm->mmap_sem);
 		vma = find_extend_vma(svm->mm, address);
 		if (!vma || address < vma->vm_start)