Re: [PATCH] system/physmem: Fix migration dirty bitmap coherency with TCG memory access

[Thomas Huth <thuth@redhat.com>]

On 19/02/2024 07.17, Nicholas Piggin wrote:
> The fastpath in cpu_physical_memory_sync_dirty_bitmap() to test large
> aligned ranges forgot to bring the TCG TLB up to date after clearing
> some of the dirty memory bitmap bits. This can result in stores though
> the TCG TLB not setting the dirty memory bitmap and ultimately causes
> memory corruption / lost updates during migration from a TCG host.
> 
> Fix this by exporting an abstracted function to call when dirty bits
> have been cleared.
> 
> Fixes: aa8dc044772 ("migration: synchronize memory bitmap 64bits at a time")
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---

Sounds promising! ... but it doesn't seem to fix the migration-test qtest 
with s390x when it gets enabled again:

diff --git a/tests/qtest/migration-test.c b/tests/qtest/migration-test.c
--- a/tests/qtest/migration-test.c
+++ b/tests/qtest/migration-test.c
@@ -3385,15 +3385,6 @@ int main(int argc, char **argv)
          return g_test_run();
      }

-    /*
-     * Similar to ppc64, s390x seems to be touchy with TCG, so disable it
-     * there until the problems are resolved
-     */
-    if (g_str_equal(arch, "s390x") && !has_kvm) {
-        g_test_message("Skipping test: s390x host with KVM is required");
-        return g_test_run();
-    }
-
      tmpfs = g_dir_make_tmp("migration-test-XXXXXX", &err);
      if (!tmpfs) {
          g_test_message("Can't create temporary directory in %s: %s",

I wonder whether there is more stuff like this necessary somewhere?

Did you try to re-enable tests/qtest/migration-test.c for ppc64 with TCG to 
see whether that works fine now?

  Thomas