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KVM: x86: Always set mp_state to RUNNABLE on wakeup from HLT

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When emulating HLT and a wake event is already pending, explicitly mark
the vCPU RUNNABLE (via kvm_set_mp_state()) instead of assuming the vCPU is
already in the appropriate state.  Barring a KVM bug, it should be
impossible for the vCPU to be in a non-RUNNABLE state, but there is no
advantage to relying on that to hold true, and ensuring the vCPU is made
RUNNABLE avoids non-deterministic behavior with respect to pv_unhalted.

E.g. if the vCPU is not already RUNNABLE, then depending on when
pv_unhalted is set, KVM could either leave the vCPU in the non-RUNNABLE
state (set before __kvm_emulate_halt()), or transition the vCPU to HALTED
and then RUNNABLE (pv_unhalted set after the kvm_vcpu_has_events() check).

Link: https://lore.kernel.org/r/20250224174156.2362059-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2025-02-24 09:41:56 -08:00
parent b50cb2b155
commit 2a289aed3f
1 changed files with 2 additions and 3 deletions
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5
arch/x86/kvm/x86.c
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@ -11297,9 +11297,8 @@ static int __kvm_emulate_halt(struct kvm_vcpu *vcpu, int state, int reason)
++vcpu->stat.halt_exits;
if (lapic_in_kernel(vcpu)) {
if (kvm_vcpu_has_events(vcpu))
vcpu->arch.pv.pv_unhalted = false;
else
kvm_set_mp_state(vcpu, state);
state = KVM_MP_STATE_RUNNABLE;
kvm_set_mp_state(vcpu, state);
return 1;
} else {
vcpu->run->exit_reason = reason;