Add notification post-livemigration by jaykrell · Pull Request #2792 · microsoft/openvmm

jaykrell · 2026-02-10T23:38:40Z

This pull request adds a notification post-livemigration.
Guests are not generally meant to be aware of live migration, but there are or soon will be exceptions, and this will support them.

Copilot

Pull request overview

This pull request adds support for post-live-migration notifications in the Guest Emulation Transport (GET) protocol. It introduces a new guest notification type that will allow the host to notify the guest when a live migration has completed, enabling the guest to take appropriate actions in response.

Changes:

Adds NOTIFY_POST_LIVE_MIGRATION guest notification to the GET protocol
Implements callback infrastructure for handling post-live-migration notifications
Integrates the notification callback setup in OpenHCL worker initialization

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 10 comments.

File	Description
vm/devices/get/get_protocol/src/lib.rs	Defines new `NOTIFY_POST_LIVE_MIGRATION` guest notification constant
vm/devices/get/guest_emulation_transport/src/process_loop.rs	Adds message type, field storage, and notification handling for post-live-migration callback
vm/devices/get/guest_emulation_transport/src/client.rs	Adds public API method to set the post-live-migration notification callback
openhcl/underhill_core/src/worker.rs	Attempts to wire up the callback in OpenHCL initialization

vm/devices/get/guest_emulation_transport/src/client.rs

vm/devices/get/guest_emulation_transport/src/process_loop.rs

vm/devices/get/guest_emulation_transport/src/client.rs

openhcl/underhill_core/src/worker.rs

vm/devices/get/guest_emulation_transport/src/process_loop.rs

vm/devices/get/get_protocol/src/lib.rs

vm/devices/get/guest_emulation_transport/src/process_loop.rs

github-actions · 2026-02-11T01:48:18Z

At least one Petri test failed.

Copilot

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

Copilot · 2026-02-12T02:57:41Z

vm/devices/get/guest_emulation_transport/src/process_loop.rs

+        &mut self,
+        _notification: get_protocol::PostLiveMigrationNotification,
+    ) {
+        tracing::info!(CVM_ALLOWED, "notify_post_live_migration");


The callback stored in self.post_live_migration is never actually invoked. Looking at the similar handle_debug_interrupt_notification function (lines 1565-1587), the callback should be called if it exists. The handler should invoke the callback like this: if let Some(callback) = self.post_live_migration.as_ref() { callback() }

Suggested change

tracing::info!(CVM_ALLOWED, "notify_post_live_migration");

tracing::info!(CVM_ALLOWED, "notify_post_live_migration");

if let Some(callback) = self.post_live_migration.as_ref() {

callback();

}

Copilot · 2026-02-12T02:57:41Z

vm/devices/get/guest_emulation_transport/src/client.rs

            .notify(msg::Msg::SetDebugInterruptCallback(callback.into()));
    }

+    /// Set the the callback to handle PostLiveMigrationNotification.


Duplicate word "the" in the comment. Should be "Set the callback to handle PostLiveMigrationNotification."

Suggested change

/// Set the the callback to handle PostLiveMigrationNotification.

/// Set the callback to handle PostLiveMigrationNotification.

Copilot · 2026-02-12T02:57:41Z

vm/devices/get/guest_emulation_transport/src/process_loop.rs

        /// Store the callback to trigger the debug interrupt.
        // TODO: Consider a strategy that avoids LocalOnly here.
        SetDebugInterruptCallback(LocalOnly<Box<dyn Fn(u8) + Send + Sync>>),
+        /// Notify that livemigration has finished.


The term should be "live migration" (two words) instead of "livemigration" (one word) for consistency with standard terminology and the rest of the codebase.

Suggested change

/// Notify that livemigration has finished.

/// Notify that live migration has finished.

More searchable this way?

mattkur · 2026-02-14T08:25:35Z

This pull request adds a notification post-livemigration. Guests are not generally meant to be aware of live migration, but there are or soon will be exceptions, and this will support them.

Thanks for this contribution, Jay! I'd like to understand more why we are changing what has been a fundamental principal of the Hyper-V Live Migration guarantees. I'm sure there's a good reason, but can you share more info? I understand if there are parts of this conversation that we need to take offline since they refer to Hyper-V behavior.

mattkur · 2026-02-14T08:31:27Z

vm/devices/get/guest_emulation_transport/src/process_loop.rs

            GuestNotifications::INJECT_DEBUG_INTERRUPT => {
                self.handle_debug_interrupt_notification(read_guest_notification(id, buf)?)?;
            }
+            GuestNotifications::NOTIFY_POST_LIVE_MIGRATION => {


This loop will silently ignore messages that it does not understand. So, when an older version of OpenHCL runs on one of the hosts that sends this message, that openhcl will ignore it. Is that safe for the scenario?

(Also: older hosts won't send this message, is that safe?)

We have no dependency on this yet, so..it should be OK?

It should. This is a notification, not a request - for clarity, the guest doesn't get a chance to veto LM.

What happens to the hardware without notification?

Should there be a vetoable check early on before migration?

jaykrell · 2026-02-16T22:53:09Z

This pull request adds a notification post-livemigration. Guests are not generally meant to be aware of live migration, but there are or soon will be exceptions, and this will support them.

Thanks for this contribution, Jay! I'd like to understand more why we are changing what has been a fundamental principal of the Hyper-V Live Migration guarantees. I'm sure there's a good reason, but can you share more info? I understand if there are parts of this conversation that we need to take offline since they refer to Hyper-V behavior.

There is hardware that will need to rederive some state when on a new host.

openhcl/underhill_core/src/worker.rs

jaykrell requested a review from a team as a code owner February 10, 2026 23:38

Copilot AI review requested due to automatic review settings February 10, 2026 23:38

Copilot started reviewing on behalf of jaykrell February 10, 2026 23:39 View session

jaykrell marked this pull request as draft February 10, 2026 23:40

Copilot AI reviewed Feb 10, 2026

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jaykrell force-pushed the dev/jaykrell/manticore-1 branch 5 times, most recently from 89cd82a to 8df0c14 Compare February 11, 2026 00:38

manticore

96f62f7

jaykrell force-pushed the dev/jaykrell/manticore-1 branch from 8df0c14 to 96f62f7 Compare February 11, 2026 00:40

jaykrell marked this pull request as ready for review February 11, 2026 00:53

jaykrell force-pushed the dev/jaykrell/manticore-1 branch from 96f62f7 to 22b442f Compare February 12, 2026 02:53

jaykrell requested a review from Copilot February 12, 2026 02:53

Copilot started reviewing on behalf of jaykrell February 12, 2026 02:54 View session

Copilot AI reviewed Feb 12, 2026

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mattkur reviewed Feb 14, 2026

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AI PR feedback.

1b6872b

jaykrell force-pushed the dev/jaykrell/manticore-1 branch from 22b442f to 1b6872b Compare February 16, 2026 23:08

cosmetic

8018f90

smalis-msft reviewed Feb 17, 2026

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openhcl/underhill_core/src/worker.rs Show resolved Hide resolved

Merge branch 'main' into dev/jaykrell/manticore-1

2d034e7

	/// Set the the callback to handle PostLiveMigrationNotification.
	/// Set the callback to handle PostLiveMigrationNotification.

	/// Notify that livemigration has finished.
	/// Notify that live migration has finished.

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github-actions bot commented Feb 11, 2026

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jaykrell commented Feb 10, 2026 •

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