On Wed, Apr 28, 2021, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
>
> Commit ee66e453db13d (KVM: lapic: Busy wait for timer to expire when
> using hv_timer) tries to set ktime->expired_tscdeadline by checking
> ktime->hv_timer_in_use since lapic timer oneshot/periodic modes which
> are emulated by vmx preemption timer also get advanced, they leverage
> the same vmx preemption timer logic with tsc-deadline mode. However,
> ktime->hv_timer_in_use is cleared before apic_timer_expired() handling,
> let's delay this clearing in preemption-disabled region.
>
> Fixes: ee66e453db13d (KVM: lapic: Busy wait for timer to expire when using hv_timer)
Well that's embarassing. I suspect/hope I tested the case where start_hv_timer()
detects the timer already expired. On the plus side, start_hv_timer() calls
cancel_hv_timer() after apic_timer_expired(), so there are unlikely to be hidden
side effects (and cancel_hv_timer() is tiny).
> Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
> arch/x86/kvm/lapic.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 152591f..c0ebef5 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1913,8 +1913,8 @@ void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
> if (!apic->lapic_timer.hv_timer_in_use)
> goto out;
> WARN_ON(rcuwait_active(&vcpu->wait));
> - cancel_hv_timer(apic);
> apic_timer_expired(apic, false);
> + cancel_hv_timer(apic);
>
> if (apic_lvtt_period(apic) && apic->lapic_timer.period) {
> advance_periodic_target_expiration(apic);
> --
> 2.7.4
>
