iommu/amd: Don't set pasid_state->mm to NULL in unbind_pasid

With calling te mmu_notifier_register function we hold a
reference to the mm_struct that needs to be released in
mmu_notifier_unregister. This is true even if the notifier
was already unregistered from exit_mmap and the .release
call-back has already run.

So make sure we call mmu_notifier_unregister unconditionally
in amd_iommu_unbind_pasid.
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Tested-by: Oded Gabbay <oded.gabbay@amd.com>

drivers/iommu/amd_iommu_v2.c

@@ -320,13 +320,6 @@ static void unbind_pasid(struct pasid_state *pasid_state)
 
 	/* Make sure no more pending faults are in the queue */
 	flush_workqueue(iommu_wq);
-
-	/*
-	 * No more faults are in the work queue and no new faults will be queued
-	 * from here on. We can safely set pasid_state->mm to NULL now as the
-	 * mm_struct might go away after we return.
-	 */
-	pasid_state->mm = NULL;
 }
 
 static void free_pasid_states_level1(struct pasid_state **tbl)
@@ -756,17 +749,10 @@ void amd_iommu_unbind_pasid(struct pci_dev *pdev, int pasid)
 	clear_pasid_state(dev_state, pasid_state->pasid);
 
 	/*
-	 * Check if pasid_state->mm is still valid. If mn_release has already
-	 * run it will be NULL and we can't (and don't need to) call
-	 * mmu_notifier_unregister() on it anymore.
+	 * Call mmu_notifier_unregister to drop our reference
+	 * to pasid_state->mm
 	 */
-	if (pasid_state->mm) {
-		/*
-		 * This will call the mn_release function and unbind
-		 * the PASID.
-		 */
-		mmu_notifier_unregister(&pasid_state->mn, pasid_state->mm);
-	}
+	mmu_notifier_unregister(&pasid_state->mn, pasid_state->mm);
 
 	put_pasid_state_wait(pasid_state); /* Reference taken in
 					      amd_iommu_pasid_bind */