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offload_daemon: Add --ondemand restore mode

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Add an --ondemand flag to the offload daemon's restore subcommand to
support the post-copy mechanism from the live migration protocol.

In on-demand mode, the daemon creates empty memfds to back the guest
memory and sends them over to the VMM. This lets the VM start quickly,
right after the memfds are mapped into CH's address space.

At runtime, when the guest accesses a page (or the prefault handler
requests it), the daemon faults it in by copying the page content into
its shared memory mapping, then replies to the PageFault request so the
VMM can consider the page present.

Signed-off-by: Sebastien Boeuf <sboeuf@meta.com>
Assisted-by: Claude:claude-opus-4-7
This commit is contained in:
Sebastien Boeuf
2026-06-02 06:11:24 -07:00
parent 48ba1f1417
commit 60398f11ff
5 changed files with 257 additions and 66 deletions
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68
cloud-hypervisor/tests/integration.rs
View File

@@ -8264,13 +8264,19 @@ mod ivshmem {
#[test]
#[cfg(not(feature = "mshv"))]
fn test_snapshot_restore_offload() {
snapshot_restore_common::_test_snapshot_restore_offload(false);
snapshot_restore_common::_test_snapshot_restore_offload(false, false);
}
#[test]
#[cfg(not(feature = "mshv"))]
fn test_snapshot_restore_offload_virtio_mem() {
snapshot_restore_common::_test_snapshot_restore_offload(true);
snapshot_restore_common::_test_snapshot_restore_offload(true, false);
}
#[test]
#[cfg(not(feature = "mshv"))]
fn test_snapshot_restore_offload_ondemand() {
snapshot_restore_common::_test_snapshot_restore_offload(false, true);
}
#[test]
@@ -8971,7 +8977,7 @@ mod snapshot_restore_common {
// Round-trip via the reference offload daemon over the existing
// `vm.send-migration local=on` / `vm.receive-migration` endpoints,
// proving parity with `vm.snapshot`/`vm.restore`.
pub(crate) fn _test_snapshot_restore_offload(virtio_mem: bool) {
pub(crate) fn _test_snapshot_restore_offload(virtio_mem: bool, ondemand: bool) {
let disk_config = UbuntuDiskConfig::new(JAMMY_IMAGE_NAME.to_string());
let guest = Guest::new(Box::new(disk_config));
let kernel_path = direct_kernel_boot_path();
@@ -9121,16 +9127,19 @@ mod snapshot_restore_common {
None
)));
// receive-migration blocks until done; run it in a thread
// so we can start the daemon as the sender in parallel.
// receive-migration blocks until done. Run it in a thread so
// we can start the daemon as the sender in parallel. On demand
// mode adds `memory_mode=postcopy`.
let api_socket_restored_clone = api_socket_restored.clone();
let restore_socket_clone = restore_socket.clone();
let ondemand_for_thread = ondemand;
let restore_thread = std::thread::spawn(move || {
remote_command(
&api_socket_restored_clone,
"receive-migration",
Some(format!("receiver_url=unix:{restore_socket_clone}").as_str()),
)
let arg = if ondemand_for_thread {
format!("receiver_url=unix:{restore_socket_clone},memory_mode=postcopy")
} else {
format!("receiver_url=unix:{restore_socket_clone}")
};
remote_command(&api_socket_restored_clone, "receive-migration", Some(&arg))
});
// Wait for CH to bind the socket before starting the daemon.
@@ -9139,26 +9148,35 @@ mod snapshot_restore_common {
}));
// Daemon in restore (sender) mode with --resume so the
// guest is live when we probe it.
// guest is live when we probe it. On demand mode adds --ondemand and
// keeps the daemon connected to serve PageFault requests.
let mut restore_args = vec![
"restore".to_string(),
"--socket".to_string(),
restore_socket.clone(),
"--input-dir".to_string(),
offload_dir.clone(),
"--resume".to_string(),
];
if ondemand {
restore_args.push("--ondemand".to_string());
}
let daemon = Command::new(clh_command("offload_daemon"))
.args([
"restore",
"--socket",
&restore_socket,
"--input-dir",
&offload_dir,
"--resume",
])
.args(&restore_args)
.stderr(Stdio::piped())
.stdout(Stdio::piped())
.spawn()
.unwrap();
let daemon_output = daemon.wait_with_output().unwrap();
assert!(
daemon_output.status.success(),
"offload daemon (restore) failed: stderr={}",
String::from_utf8_lossy(&daemon_output.stderr)
);
if ondemand {
drop(daemon);
} else {
let daemon_output = daemon.wait_with_output().unwrap();
assert!(
daemon_output.status.success(),
"offload daemon (restore) failed: stderr={}",
String::from_utf8_lossy(&daemon_output.stderr)
);
}
assert!(
restore_thread.join().unwrap(),