2022-05-11 09:44:32

by Wanpeng Li

Subject: [PATCH v2 1/2] 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, this patch does it by clearing pending
when canceling the timer.

Fixes: 4427593258 (KVM: x86: thoroughly disarm LAPIC timer around TSC deadline switch)
Signed-off-by: Wanpeng Li <[email protected]>
---
v1 -> v2:
* clear pending in cancel_apic_timer

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..6268880c8eed 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1548,6 +1548,7 @@ static void cancel_apic_timer(struct kvm_lapic *apic)
if (apic->lapic_timer.hv_timer_in_use)
cancel_hv_timer(apic);
preempt_enable();
+ atomic_set(&apic->lapic_timer.pending, 0);
}

static void apic_update_lvtt(struct kvm_lapic *apic)
--
2.25.1

2022-05-11 14:11:01

by Paolo Bonzini

Subject: Re: [PATCH v2 1/2] KVM: LAPIC: Disarm LAPIC timer includes pending timer around TSC deadline switch

On 5/11/22 04:38, Wanpeng Li wrote:
>
> Fixes: 4427593258 (KVM: x86: thoroughly disarm LAPIC timer around TSC deadline switch)
> Signed-off-by: Wanpeng Li<[email protected]>
> ---

Please write a testcase for this.

Paolo

2022-05-14 02:01:57

by Wanpeng Li

Subject: Re: [PATCH v2 1/2] KVM: LAPIC: Disarm LAPIC timer includes pending timer around TSC deadline switch

On Wed, 11 May 2022 at 21:54, Paolo Bonzini <[email protected]> wrote:
>
> On 5/11/22 04:38, Wanpeng Li wrote:
> >
> > Fixes: 4427593258 (KVM: x86: thoroughly disarm LAPIC timer around TSC deadline switch)
> > Signed-off-by: Wanpeng Li<[email protected]>
> > ---
>
> Please write a testcase for this.

Something like this, however, it is not easy to catch the pending
timer in this scenario.

diff --git a/x86/apic.c b/x86/apic.c
index 23508ad..108c1c8 100644
--- a/x86/apic.c
+++ b/x86/apic.c
@@ -22,7 +22,7 @@ static void test_lapic_existence(void)
#define TSC_DEADLINE_TIMER_VECTOR 0xef
#define BROADCAST_VECTOR 0xcf

-static int tdt_count;
+static int volatile tdt_count;

static void tsc_deadline_timer_isr(isr_regs_t *regs)
{
@@ -672,6 +672,18 @@ static void test_apic_change_mode(void)
/* now tmcct == 0 and tmict != 0 */
apic_change_mode(APIC_LVT_TIMER_PERIODIC);
report(!apic_read(APIC_TMCCT), "TMCCT should stay at zero");
+
+ handle_irq(TSC_DEADLINE_TIMER_VECTOR, tsc_deadline_timer_isr);
+ irq_enable();
+
+ apic_write(APIC_LVTT, APIC_LVT_TIMER_ONESHOT |
+ APIC_LVT_TIMER_VECTOR);
+ /* Divider == 1 */
+ apic_write(APIC_TDCR, 0x0000000b);
+
+ apic_write(APIC_TMICT, 0x999999);
+ enable_tsc_deadline_timer();
+ while(tdt_count == 1);
}

#define KVM_HC_SEND_IPI 10

2022-05-19 15:52:07

by Wanpeng Li

Subject: Re: [PATCH v2 1/2] KVM: LAPIC: Disarm LAPIC timer includes pending timer around TSC deadline switch

ping,
On Wed, 11 May 2022 at 10:39, Wanpeng Li <[email protected]> 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, this patch does it by clearing pending
> when canceling the timer.
>
> Fixes: 4427593258 (KVM: x86: thoroughly disarm LAPIC timer around TSC deadline switch)
> Signed-off-by: Wanpeng Li <[email protected]>
> ---
> v1 -> v2:
> * clear pending in cancel_apic_timer
>
> 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..6268880c8eed 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1548,6 +1548,7 @@ static void cancel_apic_timer(struct kvm_lapic *apic)
> if (apic->lapic_timer.hv_timer_in_use)
> cancel_hv_timer(apic);
> preempt_enable();
> + atomic_set(&apic->lapic_timer.pending, 0);
> }
>
> static void apic_update_lvtt(struct kvm_lapic *apic)
> --
> 2.25.1
>