xen/gnttab: leave lazy MMU mode in the case of a m2p override failure

Commit f62805f1 introduced a bug where lazy MMU mode isn't exited if a
m2p_add/remove_override call fails.
Acked-by: NStefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: NDavid Vrabel <david.vrabel@citrix.com>
Reviewed-by: NAnthony Liguori <aliguori@amazon.com>
Cc: xen-devel@lists.xenproject.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NMatt Wilson <msw@amazon.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
CC: stable@vger.kernel.org

drivers/xen/grant-table.c

@@ -930,9 +930,10 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
 		ret = m2p_add_override(mfn, pages[i], kmap_ops ?
 				       &kmap_ops[i] : NULL);
 		if (ret)
-			return ret;
+			goto out;
 	}
 
+ out:
 	if (lazy)
 		arch_leave_lazy_mmu_mode();
 
@@ -969,9 +970,10 @@ int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
 		ret = m2p_remove_override(pages[i], kmap_ops ?
 				       &kmap_ops[i] : NULL);
 		if (ret)
-			return ret;
+			goto out;
 	}
 
+ out:
 	if (lazy)
 		arch_leave_lazy_mmu_mode();