After the guest KVM file descriptor has changed as a part of the process of
confidential guest reset mechanism, existing memory needs to be reattached to
the new file descriptor. This change adds a helper function ram_block_rebind()
for this purpose. The next patch will make use of this function.

Signed-off-by: Ani Sinha <anisinha@redhat.com>
---
 include/system/physmem.h |  1 +
 system/physmem.c         | 28 ++++++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/include/system/physmem.h b/include/system/physmem.h
index 7bb7d3e154..da91b77bd9 100644
--- a/include/system/physmem.h
+++ b/include/system/physmem.h
@@ -51,5 +51,6 @@ physical_memory_snapshot_and_clear_dirty(MemoryRegion *mr, hwaddr offset,
 bool physical_memory_snapshot_get_dirty(DirtyBitmapSnapshot *snap,
                                         ram_addr_t start,
                                         ram_addr_t length);
+int ram_block_rebind(Error **errp);
 
 #endif
diff --git a/system/physmem.c b/system/physmem.c
index 2fb0c25c93..e5ff26acec 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -2826,6 +2826,34 @@ found:
     return block;
 }
 
+/*
+ * Creates new guest memfd for the ramblocks and closes the
+ * existing memfd.
+ */
+int ram_block_rebind(Error **errp)
+{
+    RAMBlock *block;
+
+    qemu_mutex_lock_ramlist();
+
+    RAMBLOCK_FOREACH(block) {
+        if (block->flags & RAM_GUEST_MEMFD) {
+            if (block->guest_memfd >= 0) {
+                close(block->guest_memfd);
+            }
+            block->guest_memfd = kvm_create_guest_memfd(block->max_length,
+                                                        0, errp);
+            if (block->guest_memfd < 0) {
+                qemu_mutex_unlock_ramlist();
+                return -1;
+            }
+
+        }
+    }
+    qemu_mutex_unlock_ramlist();
+    return 0;
+}
+
 /*
  * Finds the named RAMBlock
  *
-- 
2.42.0