perf(mshv): skip RIP advance on VmAction::Halt fast path#1476
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Signed-off-by: Ludvig Liljenberg <4257730+ludfjig@users.noreply.github.com>
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Pull request overview
Moves the VmAction::Halt fast-path check before MSHV's manual RIP advancement in MshvVm::run_vcpu()'s I/O port intercept handler. Since the next guest dispatch sets RIP via set_regs() anyway, skipping the RIP advance (either VP register page dirtying or a set_reg IOCTL fallback) on halt avoids unnecessary work on a hot path.
Changes:
- Reorder the
VmAction::Haltshort-circuit to occur before RIP advancement in the MSHV I/O port intercept path.
jsturtevant
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May 28, 2026
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Fixes an issue where we did an extra IOCTL when it wasn't needed (regs gets set anyway on next guest call).
Note that the perf regressions were mostly fixed by #1366 due to using VP page for setting registers instead of IOCTL, so the impact of this PR is minor. But it's still good to have