It's used for discarding oppsite memory after memory conversion to
shared/private.

Note, private-shared page conversion is done at 4KB granularity. Don't
check alignment with rb->page_size, instead qemu_host_page_size, which
is 4K.

Originally-from: Isaku Yamahata <isaku.yamahata@intel.com>
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
---
 include/exec/cpu-common.h |  2 ++
 softmmu/physmem.c         | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
index 87dc9a752c9a..558684b9f246 100644
--- a/include/exec/cpu-common.h
+++ b/include/exec/cpu-common.h
@@ -157,6 +157,8 @@ typedef int (RAMBlockIterFunc)(RAMBlock *rb, void *opaque);
 
 int qemu_ram_foreach_block(RAMBlockIterFunc func, void *opaque);
 int ram_block_discard_range(RAMBlock *rb, uint64_t start, size_t length);
+int ram_block_convert_range(RAMBlock *rb, uint64_t start, size_t length,
+                            bool shared_to_private);
 
 #endif
 
diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index 6ee6bc794f44..dab3247d461c 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -3733,3 +3733,39 @@ bool ram_block_discard_is_required(void)
     return qatomic_read(&ram_block_discard_required_cnt) ||
            qatomic_read(&ram_block_coordinated_discard_required_cnt);
 }
+
+int ram_block_convert_range(RAMBlock *rb, uint64_t start, size_t length,
+                            bool shared_to_private)
+{
+    int fd;
+
+    if (!rb || rb->gmem_fd < 0) {
+        return -1;
+    }
+
+    if (!QEMU_PTR_IS_ALIGNED(start, qemu_host_page_size) ||
+        !QEMU_PTR_IS_ALIGNED(length, qemu_host_page_size)) {
+        return -1;
+    }
+
+    if (!length) {
+        return -1;
+    }
+
+    if (start + length > rb->max_length) {
+        return -1;
+    }
+
+    if (shared_to_private) {
+        void *host_startaddr = rb->host + start;
+
+        if (!QEMU_PTR_IS_ALIGNED(host_startaddr, qemu_host_page_size)) {
+            return -1;
+        }
+        fd = rb->fd;
+    } else {
+        fd = rb->gmem_fd;
+    }
+
+    return ram_block_discard_range_fd(rb, start, length, fd);
+}
-- 
2.34.1