[PULL 23/25] multifd: bugfix for migration using compression methods

[Fabiano Rosas]

From: Yuan Liu <yuan1.liu@intel.com>

When compression is enabled on the migration channel and
the pages processed are all zero pages, these pages will
not be sent and updated on the target side, resulting in
incorrect memory data on the source and target sides.

The root cause is that all compression methods call
multifd_send_prepare_common to determine whether to compress
dirty pages, but multifd_send_prepare_common does not update
the IOV of MultiFDPacket_t when all dirty pages are zero pages.

The solution is to always update the IOV of MultiFDPacket_t
regardless of whether the dirty pages are all zero pages.

Fixes: 303e6f54f9 ("migration/multifd: Implement zero page transmission on the 
multifd thread.")
Cc: qemu-stable@nongnu.org #9.0+
Signed-off-by: Yuan Liu <yuan1.liu@intel.com>
Reviewed-by: Jason Zeng <jason.zeng@intel.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <20241218091413.140396-2-yuan1.liu@intel.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
---
 migration/multifd-nocomp.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/migration/multifd-nocomp.c b/migration/multifd-nocomp.c
index c1f686c0ce..1325dba97c 100644
--- a/migration/multifd-nocomp.c
+++ b/migration/multifd-nocomp.c
@@ -432,6 +432,7 @@ int multifd_ram_flush_and_sync(QEMUFile *f)
 bool multifd_send_prepare_common(MultiFDSendParams *p)
 {
     MultiFDPages_t *pages = &p->data->u.ram;
+    multifd_send_prepare_header(p);
     multifd_send_zero_page_detect(p);
 
     if (!pages->normal_num) {
@@ -439,8 +440,6 @@ bool multifd_send_prepare_common(MultiFDSendParams *p)
         return false;
     }
 
-    multifd_send_prepare_header(p);
-
     return true;
 }
 
-- 
2.35.3