* [PATCH] KVM: LAPIC: Accurately guarantee busy wait for timer to expire when using hv_timer
@ 2021-04-28 11:08 Wanpeng Li
2021-04-28 22:56 ` Sean Christopherson
0 siblings, 1 reply; 3+ messages in thread
From: Wanpeng Li @ 2021-04-28 11:08 UTC (permalink / raw)
To: linux-kernel, kvm
Cc: Paolo Bonzini, Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li,
Jim Mattson, Joerg Roedel
From: Wanpeng Li <wanpengli@tencent.com>
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)
Cc: Sean Christopherson <seanjc@google.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
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
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] KVM: LAPIC: Accurately guarantee busy wait for timer to expire when using hv_timer
2021-04-28 11:08 [PATCH] KVM: LAPIC: Accurately guarantee busy wait for timer to expire when using hv_timer Wanpeng Li
@ 2021-04-28 22:56 ` Sean Christopherson
2021-04-29 15:40 ` Paolo Bonzini
0 siblings, 1 reply; 3+ messages in thread
From: Sean Christopherson @ 2021-04-28 22:56 UTC (permalink / raw)
To: Wanpeng Li
Cc: linux-kernel, kvm, Paolo Bonzini, Vitaly Kuznetsov, Wanpeng Li,
Jim Mattson, Joerg Roedel
On Wed, Apr 28, 2021, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.com>
>
> 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@google.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
> ---
> 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
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] KVM: LAPIC: Accurately guarantee busy wait for timer to expire when using hv_timer
2021-04-28 22:56 ` Sean Christopherson
@ 2021-04-29 15:40 ` Paolo Bonzini
0 siblings, 0 replies; 3+ messages in thread
From: Paolo Bonzini @ 2021-04-29 15:40 UTC (permalink / raw)
To: Sean Christopherson, Wanpeng Li
Cc: linux-kernel, kvm, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
Joerg Roedel
On 29/04/21 00:56, Sean Christopherson wrote:
> On Wed, Apr 28, 2021, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpengli@tencent.com>
>>
>> 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@google.com>
>> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
>
> Reviewed-by: Sean Christopherson <seanjc@google.com>
>
>> ---
>> 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
>>
>
Queued, thanks.
Paolo
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2021-04-29 15:40 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2021-04-28 11:08 [PATCH] KVM: LAPIC: Accurately guarantee busy wait for timer to expire when using hv_timer Wanpeng Li
2021-04-28 22:56 ` Sean Christopherson
2021-04-29 15:40 ` Paolo Bonzini
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