exec/memory: Introduce RAM_NAMED_FILE flag

migrate_ignore_shared() is an optimization that avoids copying memory
that is visible and can be mapped on the target.  However, a
memory-backend-ram or a memory-backend-memfd block with the RAM_SHARED
flag set is not migrated when migrate_ignore_shared() is true.  This is
wrong, because the block has no named backing store, and its contents will
be lost.  To fix, ignore shared memory iff it is a named file.  Define a
new flag RAM_NAMED_FILE to distinguish this case.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <1686151116-253260-1-git-send-email-steven.sistare@oracle.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index 588d0d1..6bdd944 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -1570,6 +1570,11 @@ void qemu_ram_unset_migratable(RAMBlock *rb)
     rb->flags &= ~RAM_MIGRATABLE;
 }
 
+bool qemu_ram_is_named_file(RAMBlock *rb)
+{
+    return rb->flags & RAM_NAMED_FILE;
+}
+
 int qemu_ram_get_fd(RAMBlock *rb)
 {
     return rb->fd;
@@ -1880,7 +1885,7 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
 
     /* Just support these ram flags by now. */
     assert((ram_flags & ~(RAM_SHARED | RAM_PMEM | RAM_NORESERVE |
-                          RAM_PROTECTED)) == 0);
+                          RAM_PROTECTED | RAM_NAMED_FILE)) == 0);
 
     if (xen_enabled()) {
         error_setg(errp, "-mem-path not supported with Xen");