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Cache MSRs that should be reset in default case #1772

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Merged
ludfjig merged 1 commit into from
Aug 26, 2026
Merged

Cache MSRs that should be reset in default case #1772

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16 changes: 16 additions & 0 deletions src/hyperlight_host/src/hypervisor/virtual_machine/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -583,6 +583,17 @@ pub(crate) fn hyperv_msr_reset_indices(
vm: &dyn VirtualMachine,
guest_msrs: &[u32],
) -> std::result::Result<Vec<u32>, CreateVmError> {
// MSR probing is expensive. Cache the common case with no additional guest MSRs.
// Default VMs in a process use the same partition configuration and MSR set.
static DEFAULT: OnceLock<Vec<u32>> = OnceLock::new();

// Cache hit: no guest MSRs, so the reset set is always the same.
if guest_msrs.is_empty()
&& let Some(indices) = DEFAULT.get()
{
return Ok(indices.clone());
}

validate_guest_msrs(vm, guest_msrs)?;
let mut indices = filterless_core_reset_candidates()
.filter_map(|index| match probe_resettable(vm, index) {
Expand All @@ -602,6 +613,11 @@ pub(crate) fn hyperv_msr_reset_indices(
indices.extend(guest_msrs.iter().copied());
indices.sort_unstable();
indices.dedup();
// Populate the cache for future default VMs.
if guest_msrs.is_empty() {
// An error means another thread populated the same cache (harmless).
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let _ = DEFAULT.set(indices.clone());
}
Ok(indices)
}

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