1.8: hyperv_ic: implement SaveRestore for KVP & timesync (#4081) - #4127
Merged
Steven Malis (smalis-msft) merged 1 commit intoAug 4, 2026
Merged
Conversation
We've discovered a Linux kernel bug that results in crashes when vmbus channels are rapidly offered and rescinded, a pattern we exercise in our vmm_tests. Work around this by implementing SaveRestore for the last two relevant devices that didn't already support it. Mimic Hyper-V's behavior by regenerating the devices on restore, rather than actually saving state. A future change may make SaveRestore support non-optional, that's still under discussion. This doesn't restabilize the broken tests yet, I'll let this bake for a bit first. (cherry picked from commit 788419a)
Steven Malis (smalis-msft)
added
the
release_1.8.2607
Steven Malis (smalis-msft)
enabled auto-merge (squash)
July 31, 2026 17:20
Contributor
There was a problem hiding this comment.
Pull request overview
Backports upstream work to release/1.8.2607 to make the Hyper-V IC KVP and timesync devices participate in VMBus save/restore without rescinding/reoffering channels, as a workaround for a Linux kernel crash triggered by rapid offer/rescind cycles.
Changes:
- Implement
SaveRestoreSimpleVmbusDeviceforKvpIcandTimesyncIc, usingNoSavedStateand restarting negotiation on restore. - Update
IcPipeto be ring-memory-generic and harden version negotiation by dropping unexpected (stale) transaction responses; add unit tests for this behavior. - Add required dependencies (
vmbus_ring,test_with_tracingfor async tests).
Reviewed changes
Copilot reviewed 4 out of 5 changed files in this pull request and generated no comments.
Show a summary per file
| File | Description |
|---|---|
| vm/devices/hyperv_ic/src/timesync.rs | Enables save/restore support by restarting channel negotiation on restore (no persisted state). |
| vm/devices/hyperv_ic/src/kvp.rs | Enables save/restore support by restarting channel negotiation on restore (no persisted state). |
| vm/devices/hyperv_ic/src/common.rs | Makes IcPipe generic over ring memory and drops stale responses during negotiation; adds focused async tests. |
| vm/devices/hyperv_ic/Cargo.toml | Adds vmbus_ring dependency and test_with_tracing dev-dependency for the new tests. |
| Cargo.lock | Updates lockfile for the added dependencies. |
Chris Oo (chris-oo)
approved these changes
Aug 4, 2026
Steven Malis (smalis-msft)
merged commit Aug 4, 2026
dde8718
into
microsoft:release/1.8.2607
154 of 158 checks passed
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Backport of #4081 to
release/1.8.2607.The cherry-pick of 788419a applied cleanly onto
release/1.8.2607with no conflicts and no manual edits.Original PR: #4081
This backport PR was created by an AI agent (GitHub Copilot) on behalf of Steven Malis (@smalis-msft).