2022-05-10 10:26:08

by Wanpeng Li

Subject: [PATCH] KVM: LAPIC: Disarm LAPIC timer includes pending timer around TSC deadline switch

From: Wanpeng Li <[email protected]>

The timer is disarmed when switching between TSC deadline and other modes,
however, the pending timer is still in-flight, so let's accurately set
everything to a disarmed state.

Fixes: 4427593258 (KVM: x86: thoroughly disarm LAPIC timer around TSC deadline switch)
Signed-off-by: Wanpeng Li <[email protected]>
---
arch/x86/kvm/lapic.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 66b0eb0bda94..0274d17d91c2 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1562,6 +1562,7 @@ static void apic_update_lvtt(struct kvm_lapic *apic)
kvm_lapic_set_reg(apic, APIC_TMICT, 0);
apic->lapic_timer.period = 0;
apic->lapic_timer.tscdeadline = 0;
+ atomic_set(&apic->lapic_timer.pending, 0);
}
apic->lapic_timer.timer_mode = timer_mode;
limit_periodic_timer_frequency(apic);
--
2.25.1

2022-05-10 20:15:51

by Sean Christopherson

Subject: Re: [PATCH] KVM: LAPIC: Disarm LAPIC timer includes pending timer around TSC deadline switch

On Tue, May 10, 2022, Wanpeng Li wrote:
> From: Wanpeng Li <[email protected]>
>
> The timer is disarmed when switching between TSC deadline and other modes,
> however, the pending timer is still in-flight, so let's accurately set
> everything to a disarmed state.
>
> Fixes: 4427593258 (KVM: x86: thoroughly disarm LAPIC timer around TSC deadline switch)
> Signed-off-by: Wanpeng Li <[email protected]>
> ---
> arch/x86/kvm/lapic.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 66b0eb0bda94..0274d17d91c2 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1562,6 +1562,7 @@ static void apic_update_lvtt(struct kvm_lapic *apic)
> kvm_lapic_set_reg(apic, APIC_TMICT, 0);
> apic->lapic_timer.period = 0;
> apic->lapic_timer.tscdeadline = 0;
> + atomic_set(&apic->lapic_timer.pending, 0);

What about doing this in cancel_apic_timer()? That seems to be a more natural
place to clear pending. It's somewhat redundant since the other two callers of
cancel_apic_timer() start the timer immediately after, i.e. clear pending anyways,
but IMO it's odd to leave pending set when canceling the timer.

> }
> apic->lapic_timer.timer_mode = timer_mode;
> limit_periodic_timer_frequency(apic);
> --
> 2.25.1
>

2022-05-11 07:07:18

by Wanpeng Li

Subject: Re: [PATCH] KVM: LAPIC: Disarm LAPIC timer includes pending timer around TSC deadline switch

On Tue, 10 May 2022 at 21:43, Sean Christopherson <[email protected]> wrote:
>
> On Tue, May 10, 2022, Wanpeng Li wrote:
> > From: Wanpeng Li <[email protected]>
> >
> > The timer is disarmed when switching between TSC deadline and other modes,
> > however, the pending timer is still in-flight, so let's accurately set
> > everything to a disarmed state.
> >
> > Fixes: 4427593258 (KVM: x86: thoroughly disarm LAPIC timer around TSC deadline switch)
> > Signed-off-by: Wanpeng Li <[email protected]>
> > ---
> > arch/x86/kvm/lapic.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> > index 66b0eb0bda94..0274d17d91c2 100644
> > --- a/arch/x86/kvm/lapic.c
> > +++ b/arch/x86/kvm/lapic.c
> > @@ -1562,6 +1562,7 @@ static void apic_update_lvtt(struct kvm_lapic *apic)
> > kvm_lapic_set_reg(apic, APIC_TMICT, 0);
> > apic->lapic_timer.period = 0;
> > apic->lapic_timer.tscdeadline = 0;
> > + atomic_set(&apic->lapic_timer.pending, 0);
>
> What about doing this in cancel_apic_timer()? That seems to be a more natural
> place to clear pending. It's somewhat redundant since the other two callers of
> cancel_apic_timer() start the timer immediately after, i.e. clear pending anyways,
> but IMO it's odd to leave pending set when canceling the timer.

Do it in v2.

Wanpeng