runtime-rs: Add reclaim_guest_freed_memory qemu support

Add reclaim_guest_freed_memory config to qemu in runtime-rs.

Fixes: #10710

Signed-off-by: Hui Zhu <teawater@antgroup.com>

src/runtime-rs/config/configuration-qemu-runtime-rs.toml.in

@@ -143,6 +143,16 @@ default_maxvcpus = @DEFMAXVCPUS_QEMU@
 # > 5                --> will be set to 5
 default_bridges = @DEFBRIDGES@
 
+# Reclaim guest freed memory.
+# Enabling this will result in the VM balloon device having f_reporting=on set.
+# Then the hypervisor will use it to reclaim guest freed memory.
+# This is useful for reducing the amount of memory used by a VM.
+# Enabling this feature may sometimes reduce the speed of memory access in
+# the VM.
+#
+# Default false
+#reclaim_guest_freed_memory = true
+
 # Default memory size in MiB for SB/VM.
 # If unspecified then it will be set @DEFMEMSZ@ MiB.
 default_memory = @DEFMEMSZ@

src/runtime-rs/crates/hypervisor/src/qemu/cmdline_generator.rs

@@ -1793,6 +1793,10 @@ impl<'a> QemuCmdLine<'a> {
             qemu_cmd_line.add_scsi_controller();
         }
 
+        if config.device_info.reclaim_guest_freed_memory {
+            qemu_cmd_line.add_virtio_balloon();
+        }
+
         Ok(qemu_cmd_line)
     }
 
@@ -2007,6 +2011,11 @@ impl<'a> QemuCmdLine<'a> {
         self.devices.push(Box::new(console_socket_chardev));
     }
 
+    pub fn add_virtio_balloon(&mut self) {
+        let balloon_device = DeviceVirtioBalloon::new();
+        self.devices.push(Box::new(balloon_device));
+    }
+
     pub async fn build(&self) -> Result<Vec<String>> {
         let mut result = Vec::new();
 
@@ -2071,3 +2080,22 @@ fn get_devno_ccw(ccw_subchannel: &mut Option<CcwSubChannel>, device_name: &str)
         )
     })
 }
+
+#[derive(Debug)]
+struct DeviceVirtioBalloon {}
+
+impl DeviceVirtioBalloon {
+    fn new() -> Self {
+        DeviceVirtioBalloon {}
+    }
+}
+
+#[async_trait]
+impl ToQemuParams for DeviceVirtioBalloon {
+    async fn qemu_params(&self) -> Result<Vec<String>> {
+        Ok(vec![
+            "-device".to_owned(),
+            "virtio-balloon,free-page-reporting=on".to_owned(),
+        ])
+    }
+}