Cache MSRs that should be reset in default case - #1772
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August 26, 2026 18:15
Signed-off-by: Ludvig Liljenberg <4257730+ludfjig@users.noreply.github.com>
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Pull request overview
This PR reduces VM creation latency for Hyper-V style backends (MSHV on Linux, WHP on Windows) by caching the probed “MSRs to reset” index set when no additional guest MSRs are configured. This targets the common default path where SandboxConfiguration::guest_msrs(&[u8]) yields an empty list.
Changes:
- Add a
OnceLock<Vec<u32>>cache for the default (no extra guest MSRs) MSR reset index set inhyperv_msr_reset_indices. - Skip expensive MSR probing on cache hits by returning the cached index list.
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Cache probed MSRs when no additional msrs have been configured in
SandboxConfiguration::guest_msrs(&[u8]). Note the first sandbox will still be slow, but the rest will be fast.create_initialized: 2.251 ms → 1.443 ms, saving 0.808 ms (36%) per creation.
sandbox_from_snapshot: 1.450 ms → 0.682 ms, saving 0.768 ms (53%) per creation.