fix(vmm/persist): do not close uffd socket #5122
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## main #5122 +/- ##
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Files 250 250
Lines 26918 26920 +2
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Misses 4552 4552
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We prevent Rust from closing the socket file descriptor to avoid a potential race condition between the mappings message and the connection shutdown. If the latter arrives at the UFFD handler first, the handler never sees the mappings. Signed-off-by: Nikita Kalyazin <[email protected]>
bchalios
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Mar 28, 2025
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Status: Awaiting review
bchalios
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roypat
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xmarcalx
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maggie-lou
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Oct 30, 2025
Also includes this patch: firecracker-microvm/firecracker#5494 I'm interested in these bug fixes since v1.11.0 (which we were on previously): firecracker-microvm/firecracker#5122 firecracker-microvm/firecracker#5260 We should also look into enabling PCI. From their release notes: > In our micro-benchmarks, we measured up to 50% better latency for block and network, up to 70% better block throughput, and up to 25% higher network throughput (results depend on instance type and kernel). Also I had previously cherry-picked a firecracker patch that fixed some of the rcu_sched failures. It was formally merged into the firecracker repo [here](firecracker-microvm/firecracker#5494) and this final version has some implementation differences from the patch we'd applied. I can't directly apply the updated patch on v1.11.0 due to some merge conflicts, but it applies cleanly on top of v1.13.0
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Changes
Do not close the UFFD UDS socket.
Reason
We prevent Rust from closing the socket file descriptor to avoid a potential race condition between the mappings message and the connection shutdown. If the latter arrives at the UFFD handler first, the handler never sees the mappings. No meaningful test is possible due to the rare nature of the issue.
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CONTRIBUTING.md.PR Checklist
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how they are solving the problem in a clear and encompassing way.
[ ] I have updated any relevant documentation (both in code and in the docs)in the PR.
CHANGELOG.md.[ ] If a specific issue led to this PR, this PR closes the issue.[ ] When making API changes, I have followed theRunbook for Firecracker API changes.
integration tests.
[ ] I have linked an issue to every newTODO.rust-vmm.