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perf(mshv): skip RIP advance on VmAction::Halt fast path #1476

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Merged
jsturtevant merged 1 commit into from
May 28, 2026
+15 −13
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perf(mshv): skip RIP advance on VmAction::Halt fast path #1476

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28 changes: 15 additions & 13 deletions src/hyperlight_host/src/hypervisor/virtual_machine/mshv/x86_64.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -220,6 +220,21 @@ impl VirtualMachine for MshvVm {
let instruction_length = io_message.header.instruction_length() as u64;
let is_write = io_message.header.intercept_access_type != 0;

// VmAction::Halt always means "I'm done", regardless of
// whether a timer is active. The next guest dispatch
// rewrites RIP via set_regs(), so skip the RIP advance on
// this hot path.
if is_write && port_number == VmAction::Halt as u16 {
// Stop the timer thread before returning.
#[cfg(feature = "hw-interrupts")]
{
if let Some(mut t) = self.timer.take() {
t.stop();
}
}
return Ok(VmExit::Halt());
}

// mshv, unlike kvm, does not automatically increment RIP.
if let Some(page) = self
.vcpu_fd
Expand All @@ -245,19 +260,6 @@ impl VirtualMachine for MshvVm {
.map_err(|e| RunVcpuError::IncrementRip(e.into()))?;
}

// VmAction::Halt always means "I'm done", regardless
// of whether a timer is active.
if is_write && port_number == VmAction::Halt as u16 {
// Stop the timer thread before returning.
#[cfg(feature = "hw-interrupts")]
{
if let Some(mut t) = self.timer.take() {
t.stop();
}
}
return Ok(VmExit::Halt());
}

#[cfg(feature = "hw-interrupts")]
{
if is_write {
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