migration/ram: Fix error handling in ram_write_tracking_start()

If something goes wrong during uffd_change_protection(), we would miss
to unregister uffd-wp and not release our reference. Fix it by
performing the uffd_change_protection(true) last.

Note that a uffd_change_protection(false) on the recovery path without a
prior uffd_change_protection(false) is fine.

Fixes: 278e2f551a09 ("migration: support UFFD write fault processing in ram_save_iterate()")
Cc: qemu-stable@nongnu.org
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

diff --git a/migration/ram.c b/migration/ram.c
index ba228eead4bfd6a435aafb0959fa584cc9fe1999..73e5ca93e59225e2294f59e1318040393c29861c 100644 (file)
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1896,13 +1896,14 @@ int ram_write_tracking_start(void)
                 block->max_length, UFFDIO_REGISTER_MODE_WP, NULL)) {
             goto fail;
         }
+        block->flags |= RAM_UF_WRITEPROTECT;
+        memory_region_ref(block->mr);
+
         /* Apply UFFD write protection to the block memory range */
         if (uffd_change_protection(rs->uffdio_fd, block->host,
                 block->max_length, true, false)) {
             goto fail;
         }
-        block->flags |= RAM_UF_WRITEPROTECT;
-        memory_region_ref(block->mr);
 
         trace_ram_write_tracking_ramblock_start(block->idstr, block->page_size,
                 block->host, block->max_length);