Re: [PATCH 5/5] KVM: LAPIC: add APIC Timer periodic/oneshot mode VMX preemption timer support

[Wanpeng Li]

2016-10-21 2:10 GMT+08:00 Radim Krčmář :
> 2016-10-20 06:57+0800, Wanpeng Li:
>> 2016-10-20 3:28 GMT+08:00 Radim Krčmář :
>>> I think it would be better to add a function to advance the periodic
>>> timer and use it in kvm_lapic_expired_hv_timer() and in apic_timer_fn().
>>>
>>> The function can be simpler than set_target_expiration(), because it
>>> just adds the period to an existing timer.  Periodic timer will also be
>>> better then, because the period will not depend on KVM's latency when
>>> rearming.
>>
>> Good point, what's the function name do you like? How about
>> advance_target_expiration()?
>
> Sounds good, I'd just slap periodic somewhere,
> advance_periodic_target_expiration()?

Cool, thanks for your review. :)

Regards,
Wanpeng Li

Re: [PATCH 5/5] KVM: LAPIC: add APIC Timer periodic/oneshot mode VMX preemption timer support

[Wanpeng Li]

2016-10-21 2:10 GMT+08:00 Radim Krčmář :
> 2016-10-20 06:57+0800, Wanpeng Li:
>> 2016-10-20 3:28 GMT+08:00 Radim Krčmář :
>>> I think it would be better to add a function to advance the periodic
>>> timer and use it in kvm_lapic_expired_hv_timer() and in apic_timer_fn().
>>>
>>> The function can be simpler than set_target_expiration(), because it
>>> just adds the period to an existing timer.  Periodic timer will also be
>>> better then, because the period will not depend on KVM's latency when
>>> rearming.
>>
>> Good point, what's the function name do you like? How about
>> advance_target_expiration()?
>
> Sounds good, I'd just slap periodic somewhere,
> advance_periodic_target_expiration()?

Cool, thanks for your review. :)

Regards,
Wanpeng Li

Re: [PATCH 5/5] KVM: LAPIC: add APIC Timer periodic/oneshot mode VMX preemption timer support

[Radim Krčmář]

2016-10-20 06:57+0800, Wanpeng Li:
> 2016-10-20 3:28 GMT+08:00 Radim Krčmář :
>> I think it would be better to add a function to advance the periodic
>> timer and use it in kvm_lapic_expired_hv_timer() and in apic_timer_fn().
>>
>> The function can be simpler than set_target_expiration(), because it
>> just adds the period to an existing timer.  Periodic timer will also be
>> better then, because the period will not depend on KVM's latency when
>> rearming.
> 
> Good point, what's the function name do you like? How about
> advance_target_expiration()?

Sounds good, I'd just slap periodic somewhere,
advance_periodic_target_expiration()?

Re: [PATCH 5/5] KVM: LAPIC: add APIC Timer periodic/oneshot mode VMX preemption timer support

[Radim Krčmář]

2016-10-20 06:57+0800, Wanpeng Li:
> 2016-10-20 3:28 GMT+08:00 Radim Krčmář :
>> I think it would be better to add a function to advance the periodic
>> timer and use it in kvm_lapic_expired_hv_timer() and in apic_timer_fn().
>>
>> The function can be simpler than set_target_expiration(), because it
>> just adds the period to an existing timer.  Periodic timer will also be
>> better then, because the period will not depend on KVM's latency when
>> rearming.
> 
> Good point, what's the function name do you like? How about
> advance_target_expiration()?

Sounds good, I'd just slap periodic somewhere,
advance_periodic_target_expiration()?

Re: [PATCH 5/5] KVM: LAPIC: add APIC Timer periodic/oneshot mode VMX preemption timer support

[Wanpeng Li]

2016-10-20 3:28 GMT+08:00 Radim Krčmář :
> 2016-10-17 15:45+0800, Wanpeng Li:
>> From: Wanpeng Li 
>>
>> Most windows guests still utilize APIC Timer periodic/oneshot mode
>> instead of tsc-deadline mode, and the APIC Timer periodic/oneshot
>> mode are still emulated by high overhead hrtimer on host. This patch
>> converts the expected expire time of the periodic/oneshot mode to
>> guest deadline tsc in order to leverage VMX preemption timer logic
>> for APIC Timer tsc-deadline mode. After each preemption timer vmexit
>> preemption timer is restarted to emulate LVTT current-count register
>> is automatically reloaded from the initial-count register when the
>> count reaches 0. This patch reduces ~3800 cycles for each APIC Timer
>> periodic mode operation virtualization.
>>
>> Cc: Paolo Bonzini 
>> Cc: Radim Krčmář 
>> Cc: Yunhong Jiang 
>> Signed-off-by: Wanpeng Li 
>> ---
>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
>> @@ -1090,7 +1090,7 @@ static void apic_send_ipi(struct kvm_lapic *apic)
>>
>>  static u32 apic_get_tmcct(struct kvm_lapic *apic)
>>  {
>> - ktime_t remaining;
>> + ktime_t remaining, now;
>>   s64 ns;
>>   u32 tmcct;
>>
>> @@ -1101,7 +1101,8 @@ static u32 apic_get_tmcct(struct kvm_lapic *apic)
>>   apic->lapic_timer.period == 0)
>>   return 0;
>>
>> - remaining = hrtimer_get_remaining(>lapic_timer.timer);
>> + now = apic->lapic_timer.timer.base->get_time();
>> + remaining = ktime_sub(apic->lapic_timer.target_expiration, now);
>
> Periodic timer does not advance apic->lapic_timer.target_expiration,
> when rearming the hrtimer, so this would incorrectly return 0 in
> subsequent periods.

Agreed.

>
>>   if (ktime_to_ns(remaining) < 0)
>>   remaining = ktime_set(0, 0);
>>
>> @@ -1438,14 +1447,42 @@ static bool start_hv_timer(struct kvm_lapic *apic)
>>   return apic->lapic_timer.hv_timer_in_use;
>>  }
>>
>> +void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
>> +{
>> + struct kvm_lapic *apic = vcpu->arch.apic;
>> +
>> + WARN_ON(!apic->lapic_timer.hv_timer_in_use);
>> + WARN_ON(swait_active(>wq));
>> + cancel_hv_timer(apic);
>> + apic_timer_expired(apic);
>> +
>> + if (apic_lvtt_period(apic) &&
>> + set_target_expiration(apic) &&
>> + !start_hv_timer(apic))
>> + start_sw_period(apic);
>> +}
>> +EXPORT_SYMBOL_GPL(kvm_lapic_expired_hv_timer);
>> +
>>  void kvm_lapic_switch_to_hv_timer(struct kvm_vcpu *vcpu)
>>  {
>>   struct kvm_lapic *apic = vcpu->arch.apic;
>>
>>   WARN_ON(apic->lapic_timer.hv_timer_in_use);
>>
>> - if (apic_lvtt_tscdeadline(apic))
>> - start_hv_timer(apic);
>> + if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic)) {
>> + ktime_t remaining, now;
>> + u64 tscl = rdtsc();
>> +
>> + now = apic->lapic_timer.timer.base->get_time();
>> + remaining = hrtimer_get_remaining(>lapic_timer.timer);
>> + if (ktime_to_ns(remaining) < 0)
>> + remaining = ktime_set(0, 0);
>> +
>> + apic->lapic_timer.tscdeadline = kvm_read_l1_tsc(apic->vcpu, 
>> tscl) +
>> + nsec_to_cycles(apic->vcpu, ktime_to_ns(remaining));
>> + apic->lapic_timer.target_expiration = ktime_add_ns(now, 
>> ktime_to_ns(remaining));
>
> For oneshot timer, there is no need to hrtimer_get_remaining(), because
> apic->lapic_timer.tscdeadline and apic->lapic_timer.target_expiration
> are already correct, so we could just use them.

Agreed.

>
> The same could be true for the periodic timer as well, but
> apic->lapic_timer.target_expiration nor apic->lapic_timer.tscdeadline is
> advanced in apic_timer_fn(), so they are soon incorrect.

Yeah, I catch this when testing.

>
> I think it would be better to add a function to advance the periodic
> timer and use it in kvm_lapic_expired_hv_timer() and in apic_timer_fn().
>
> The function can be simpler than set_target_expiration(), because it
> just adds the period to an existing timer.  Periodic timer will also be
> better then, because the period will not depend on KVM's latency when
> rearming.

Good point, what's the function name do you like? How about
advance_target_expiration()?

>
>> + }
>> + start_hv_timer(apic);
>>  }
>>  EXPORT_SYMBOL_GPL(kvm_lapic_switch_to_hv_timer);
>>
>> @@ -1462,7 +1499,10 @@ void kvm_lapic_switch_to_sw_timer(struct kvm_vcpu 
>> *vcpu)
>>   if (atomic_read(>lapic_timer.pending))
>>   return;
>>
>> - start_sw_tscdeadline(apic);
>> + if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic))
>> + start_sw_period(apic);
>> + else if (apic_lvtt_tscdeadline(apic))
>> + start_sw_tscdeadline(apic);
>>  }
>>  EXPORT_SYMBOL_GPL(kvm_lapic_switch_to_sw_timer);
>>
>> @@ -1470,9 +1510,11 

Re: [PATCH 5/5] KVM: LAPIC: add APIC Timer periodic/oneshot mode VMX preemption timer support

[Wanpeng Li]

2016-10-20 3:28 GMT+08:00 Radim Krčmář :
> 2016-10-17 15:45+0800, Wanpeng Li:
>> From: Wanpeng Li 
>>
>> Most windows guests still utilize APIC Timer periodic/oneshot mode
>> instead of tsc-deadline mode, and the APIC Timer periodic/oneshot
>> mode are still emulated by high overhead hrtimer on host. This patch
>> converts the expected expire time of the periodic/oneshot mode to
>> guest deadline tsc in order to leverage VMX preemption timer logic
>> for APIC Timer tsc-deadline mode. After each preemption timer vmexit
>> preemption timer is restarted to emulate LVTT current-count register
>> is automatically reloaded from the initial-count register when the
>> count reaches 0. This patch reduces ~3800 cycles for each APIC Timer
>> periodic mode operation virtualization.
>>
>> Cc: Paolo Bonzini 
>> Cc: Radim Krčmář 
>> Cc: Yunhong Jiang 
>> Signed-off-by: Wanpeng Li 
>> ---
>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
>> @@ -1090,7 +1090,7 @@ static void apic_send_ipi(struct kvm_lapic *apic)
>>
>>  static u32 apic_get_tmcct(struct kvm_lapic *apic)
>>  {
>> - ktime_t remaining;
>> + ktime_t remaining, now;
>>   s64 ns;
>>   u32 tmcct;
>>
>> @@ -1101,7 +1101,8 @@ static u32 apic_get_tmcct(struct kvm_lapic *apic)
>>   apic->lapic_timer.period == 0)
>>   return 0;
>>
>> - remaining = hrtimer_get_remaining(>lapic_timer.timer);
>> + now = apic->lapic_timer.timer.base->get_time();
>> + remaining = ktime_sub(apic->lapic_timer.target_expiration, now);
>
> Periodic timer does not advance apic->lapic_timer.target_expiration,
> when rearming the hrtimer, so this would incorrectly return 0 in
> subsequent periods.

Agreed.

>
>>   if (ktime_to_ns(remaining) < 0)
>>   remaining = ktime_set(0, 0);
>>
>> @@ -1438,14 +1447,42 @@ static bool start_hv_timer(struct kvm_lapic *apic)
>>   return apic->lapic_timer.hv_timer_in_use;
>>  }
>>
>> +void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
>> +{
>> + struct kvm_lapic *apic = vcpu->arch.apic;
>> +
>> + WARN_ON(!apic->lapic_timer.hv_timer_in_use);
>> + WARN_ON(swait_active(>wq));
>> + cancel_hv_timer(apic);
>> + apic_timer_expired(apic);
>> +
>> + if (apic_lvtt_period(apic) &&
>> + set_target_expiration(apic) &&
>> + !start_hv_timer(apic))
>> + start_sw_period(apic);
>> +}
>> +EXPORT_SYMBOL_GPL(kvm_lapic_expired_hv_timer);
>> +
>>  void kvm_lapic_switch_to_hv_timer(struct kvm_vcpu *vcpu)
>>  {
>>   struct kvm_lapic *apic = vcpu->arch.apic;
>>
>>   WARN_ON(apic->lapic_timer.hv_timer_in_use);
>>
>> - if (apic_lvtt_tscdeadline(apic))
>> - start_hv_timer(apic);
>> + if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic)) {
>> + ktime_t remaining, now;
>> + u64 tscl = rdtsc();
>> +
>> + now = apic->lapic_timer.timer.base->get_time();
>> + remaining = hrtimer_get_remaining(>lapic_timer.timer);
>> + if (ktime_to_ns(remaining) < 0)
>> + remaining = ktime_set(0, 0);
>> +
>> + apic->lapic_timer.tscdeadline = kvm_read_l1_tsc(apic->vcpu, 
>> tscl) +
>> + nsec_to_cycles(apic->vcpu, ktime_to_ns(remaining));
>> + apic->lapic_timer.target_expiration = ktime_add_ns(now, 
>> ktime_to_ns(remaining));
>
> For oneshot timer, there is no need to hrtimer_get_remaining(), because
> apic->lapic_timer.tscdeadline and apic->lapic_timer.target_expiration
> are already correct, so we could just use them.

Agreed.

>
> The same could be true for the periodic timer as well, but
> apic->lapic_timer.target_expiration nor apic->lapic_timer.tscdeadline is
> advanced in apic_timer_fn(), so they are soon incorrect.

Yeah, I catch this when testing.

>
> I think it would be better to add a function to advance the periodic
> timer and use it in kvm_lapic_expired_hv_timer() and in apic_timer_fn().
>
> The function can be simpler than set_target_expiration(), because it
> just adds the period to an existing timer.  Periodic timer will also be
> better then, because the period will not depend on KVM's latency when
> rearming.

Good point, what's the function name do you like? How about
advance_target_expiration()?

>
>> + }
>> + start_hv_timer(apic);
>>  }
>>  EXPORT_SYMBOL_GPL(kvm_lapic_switch_to_hv_timer);
>>
>> @@ -1462,7 +1499,10 @@ void kvm_lapic_switch_to_sw_timer(struct kvm_vcpu 
>> *vcpu)
>>   if (atomic_read(>lapic_timer.pending))
>>   return;
>>
>> - start_sw_tscdeadline(apic);
>> + if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic))
>> + start_sw_period(apic);
>> + else if (apic_lvtt_tscdeadline(apic))
>> + start_sw_tscdeadline(apic);
>>  }
>>  EXPORT_SYMBOL_GPL(kvm_lapic_switch_to_sw_timer);
>>
>> @@ -1470,9 +1510,11 @@ static void start_apic_timer(struct kvm_lapic *apic)
>>  {
>>   atomic_set(>lapic_timer.pending, 0);
>>
>> - if 

Re: [PATCH 5/5] KVM: LAPIC: add APIC Timer periodic/oneshot mode VMX preemption timer support

[Radim Krčmář]

2016-10-17 15:45+0800, Wanpeng Li:
> From: Wanpeng Li 
> 
> Most windows guests still utilize APIC Timer periodic/oneshot mode
> instead of tsc-deadline mode, and the APIC Timer periodic/oneshot
> mode are still emulated by high overhead hrtimer on host. This patch
> converts the expected expire time of the periodic/oneshot mode to
> guest deadline tsc in order to leverage VMX preemption timer logic
> for APIC Timer tsc-deadline mode. After each preemption timer vmexit
> preemption timer is restarted to emulate LVTT current-count register
> is automatically reloaded from the initial-count register when the
> count reaches 0. This patch reduces ~3800 cycles for each APIC Timer
> periodic mode operation virtualization.
> 
> Cc: Paolo Bonzini 
> Cc: Radim Krčmář 
> Cc: Yunhong Jiang 
> Signed-off-by: Wanpeng Li 
> ---
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> @@ -1090,7 +1090,7 @@ static void apic_send_ipi(struct kvm_lapic *apic)
>  
>  static u32 apic_get_tmcct(struct kvm_lapic *apic)
>  {
> - ktime_t remaining;
> + ktime_t remaining, now;
>   s64 ns;
>   u32 tmcct;
>  
> @@ -1101,7 +1101,8 @@ static u32 apic_get_tmcct(struct kvm_lapic *apic)
>   apic->lapic_timer.period == 0)
>   return 0;
>  
> - remaining = hrtimer_get_remaining(>lapic_timer.timer);
> + now = apic->lapic_timer.timer.base->get_time();
> + remaining = ktime_sub(apic->lapic_timer.target_expiration, now);

Periodic timer does not advance apic->lapic_timer.target_expiration,
when rearming the hrtimer, so this would incorrectly return 0 in
subsequent periods.

>   if (ktime_to_ns(remaining) < 0)
>   remaining = ktime_set(0, 0);
>  
> @@ -1438,14 +1447,42 @@ static bool start_hv_timer(struct kvm_lapic *apic)
>   return apic->lapic_timer.hv_timer_in_use;
>  }
>  
> +void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
> +{
> + struct kvm_lapic *apic = vcpu->arch.apic;
> +
> + WARN_ON(!apic->lapic_timer.hv_timer_in_use);
> + WARN_ON(swait_active(>wq));
> + cancel_hv_timer(apic);
> + apic_timer_expired(apic);
> +
> + if (apic_lvtt_period(apic) &&
> + set_target_expiration(apic) &&
> + !start_hv_timer(apic))
> + start_sw_period(apic);
> +}
> +EXPORT_SYMBOL_GPL(kvm_lapic_expired_hv_timer);
> +
>  void kvm_lapic_switch_to_hv_timer(struct kvm_vcpu *vcpu)
>  {
>   struct kvm_lapic *apic = vcpu->arch.apic;
>  
>   WARN_ON(apic->lapic_timer.hv_timer_in_use);
>  
> - if (apic_lvtt_tscdeadline(apic))
> - start_hv_timer(apic);
> + if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic)) {
> + ktime_t remaining, now;
> + u64 tscl = rdtsc();
> +
> + now = apic->lapic_timer.timer.base->get_time();
> + remaining = hrtimer_get_remaining(>lapic_timer.timer);
> + if (ktime_to_ns(remaining) < 0)
> + remaining = ktime_set(0, 0);
> +
> + apic->lapic_timer.tscdeadline = kvm_read_l1_tsc(apic->vcpu, 
> tscl) +
> + nsec_to_cycles(apic->vcpu, ktime_to_ns(remaining));
> + apic->lapic_timer.target_expiration = ktime_add_ns(now, 
> ktime_to_ns(remaining));

For oneshot timer, there is no need to hrtimer_get_remaining(), because
apic->lapic_timer.tscdeadline and apic->lapic_timer.target_expiration
are already correct, so we could just use them.

The same could be true for the periodic timer as well, but
apic->lapic_timer.target_expiration nor apic->lapic_timer.tscdeadline is
advanced in apic_timer_fn(), so they are soon incorrect.

I think it would be better to add a function to advance the periodic
timer and use it in kvm_lapic_expired_hv_timer() and in apic_timer_fn().

The function can be simpler than set_target_expiration(), because it
just adds the period to an existing timer.  Periodic timer will also be
better then, because the period will not depend on KVM's latency when
rearming.

> + }
> + start_hv_timer(apic);
>  }
>  EXPORT_SYMBOL_GPL(kvm_lapic_switch_to_hv_timer);
>  
> @@ -1462,7 +1499,10 @@ void kvm_lapic_switch_to_sw_timer(struct kvm_vcpu 
> *vcpu)
>   if (atomic_read(>lapic_timer.pending))
>   return;
>  
> - start_sw_tscdeadline(apic);
> + if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic))
> + start_sw_period(apic);
> + else if (apic_lvtt_tscdeadline(apic))
> + start_sw_tscdeadline(apic);
>  }
>  EXPORT_SYMBOL_GPL(kvm_lapic_switch_to_sw_timer);
>  
> @@ -1470,9 +1510,11 @@ static void start_apic_timer(struct kvm_lapic *apic)
>  {
>   atomic_set(>lapic_timer.pending, 0);
>  
> - if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic))
> - start_sw_period(apic);
> - else if (apic_lvtt_tscdeadline(apic)) {
> + if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic)) 

Re: [PATCH 5/5] KVM: LAPIC: add APIC Timer periodic/oneshot mode VMX preemption timer support

[Radim Krčmář]

2016-10-17 15:45+0800, Wanpeng Li:
> From: Wanpeng Li 
> 
> Most windows guests still utilize APIC Timer periodic/oneshot mode
> instead of tsc-deadline mode, and the APIC Timer periodic/oneshot
> mode are still emulated by high overhead hrtimer on host. This patch
> converts the expected expire time of the periodic/oneshot mode to
> guest deadline tsc in order to leverage VMX preemption timer logic
> for APIC Timer tsc-deadline mode. After each preemption timer vmexit
> preemption timer is restarted to emulate LVTT current-count register
> is automatically reloaded from the initial-count register when the
> count reaches 0. This patch reduces ~3800 cycles for each APIC Timer
> periodic mode operation virtualization.
> 
> Cc: Paolo Bonzini 
> Cc: Radim Krčmář 
> Cc: Yunhong Jiang 
> Signed-off-by: Wanpeng Li 
> ---
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> @@ -1090,7 +1090,7 @@ static void apic_send_ipi(struct kvm_lapic *apic)
>  
>  static u32 apic_get_tmcct(struct kvm_lapic *apic)
>  {
> - ktime_t remaining;
> + ktime_t remaining, now;
>   s64 ns;
>   u32 tmcct;
>  
> @@ -1101,7 +1101,8 @@ static u32 apic_get_tmcct(struct kvm_lapic *apic)
>   apic->lapic_timer.period == 0)
>   return 0;
>  
> - remaining = hrtimer_get_remaining(>lapic_timer.timer);
> + now = apic->lapic_timer.timer.base->get_time();
> + remaining = ktime_sub(apic->lapic_timer.target_expiration, now);

Periodic timer does not advance apic->lapic_timer.target_expiration,
when rearming the hrtimer, so this would incorrectly return 0 in
subsequent periods.

>   if (ktime_to_ns(remaining) < 0)
>   remaining = ktime_set(0, 0);
>  
> @@ -1438,14 +1447,42 @@ static bool start_hv_timer(struct kvm_lapic *apic)
>   return apic->lapic_timer.hv_timer_in_use;
>  }
>  
> +void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
> +{
> + struct kvm_lapic *apic = vcpu->arch.apic;
> +
> + WARN_ON(!apic->lapic_timer.hv_timer_in_use);
> + WARN_ON(swait_active(>wq));
> + cancel_hv_timer(apic);
> + apic_timer_expired(apic);
> +
> + if (apic_lvtt_period(apic) &&
> + set_target_expiration(apic) &&
> + !start_hv_timer(apic))
> + start_sw_period(apic);
> +}
> +EXPORT_SYMBOL_GPL(kvm_lapic_expired_hv_timer);
> +
>  void kvm_lapic_switch_to_hv_timer(struct kvm_vcpu *vcpu)
>  {
>   struct kvm_lapic *apic = vcpu->arch.apic;
>  
>   WARN_ON(apic->lapic_timer.hv_timer_in_use);
>  
> - if (apic_lvtt_tscdeadline(apic))
> - start_hv_timer(apic);
> + if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic)) {
> + ktime_t remaining, now;
> + u64 tscl = rdtsc();
> +
> + now = apic->lapic_timer.timer.base->get_time();
> + remaining = hrtimer_get_remaining(>lapic_timer.timer);
> + if (ktime_to_ns(remaining) < 0)
> + remaining = ktime_set(0, 0);
> +
> + apic->lapic_timer.tscdeadline = kvm_read_l1_tsc(apic->vcpu, 
> tscl) +
> + nsec_to_cycles(apic->vcpu, ktime_to_ns(remaining));
> + apic->lapic_timer.target_expiration = ktime_add_ns(now, 
> ktime_to_ns(remaining));

For oneshot timer, there is no need to hrtimer_get_remaining(), because
apic->lapic_timer.tscdeadline and apic->lapic_timer.target_expiration
are already correct, so we could just use them.

The same could be true for the periodic timer as well, but
apic->lapic_timer.target_expiration nor apic->lapic_timer.tscdeadline is
advanced in apic_timer_fn(), so they are soon incorrect.

I think it would be better to add a function to advance the periodic
timer and use it in kvm_lapic_expired_hv_timer() and in apic_timer_fn().

The function can be simpler than set_target_expiration(), because it
just adds the period to an existing timer.  Periodic timer will also be
better then, because the period will not depend on KVM's latency when
rearming.

> + }
> + start_hv_timer(apic);
>  }
>  EXPORT_SYMBOL_GPL(kvm_lapic_switch_to_hv_timer);
>  
> @@ -1462,7 +1499,10 @@ void kvm_lapic_switch_to_sw_timer(struct kvm_vcpu 
> *vcpu)
>   if (atomic_read(>lapic_timer.pending))
>   return;
>  
> - start_sw_tscdeadline(apic);
> + if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic))
> + start_sw_period(apic);
> + else if (apic_lvtt_tscdeadline(apic))
> + start_sw_tscdeadline(apic);
>  }
>  EXPORT_SYMBOL_GPL(kvm_lapic_switch_to_sw_timer);
>  
> @@ -1470,9 +1510,11 @@ static void start_apic_timer(struct kvm_lapic *apic)
>  {
>   atomic_set(>lapic_timer.pending, 0);
>  
> - if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic))
> - start_sw_period(apic);
> - else if (apic_lvtt_tscdeadline(apic)) {
> + if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic)) {
> + if (set_target_expiration(apic) &&
> + !(kvm_x86_ops->set_hv_timer && 

Re: [PATCH 5/5] KVM: LAPIC: add APIC Timer periodic/oneshot mode VMX preemption timer support

[Paolo Bonzini]

On 17/10/2016 09:45, Wanpeng Li wrote:
> + remaining = ktime_sub(apic->lapic_timer.target_expiration, now);
>   if (ktime_to_ns(remaining) < 0)
>   remaining = ktime_set(0, 0);
>  
> @@ -1351,13 +1352,28 @@ static void start_sw_period(struct kvm_lapic *apic)
>  {
>   ktime_t now;
>  
> - /* lapic timer in oneshot or periodic mode */
> + now = apic->lapic_timer.timer.base->get_time();
> +
> + if (likely(ktime_compare(apic->lapic_timer.target_expiration, now)))

ktime_after, not ktime_compare.  Can be fixed on commit, I guess.

Paolo

> + hrtimer_start(>lapic_timer.timer,
> + apic->lapic_timer.target_expiration,
> + HRTIMER_MODE_ABS_PINNED);
> + else
> + apic_timer_expired(apic);
> +}
> +
> +static bool set_target_expiration(struct kvm_lapic *apic)
> +{
> + ktime_t now;
> + u64 tscl = rdtsc();
> +
>   now = apic->lapic_timer.timer.base->get_time();
>   apic->lapic_timer.period = (u64)kvm_lapic_get_reg(apic, APIC_TMICT)
> - * APIC_BUS_CYCLE_NS * apic->divide_count;
> + * APIC_BUS_CYCLE_NS * apic->divide_count;
>  
>   if (!apic->lapic_timer.period)
> - return;
> + return false;
>   /*
>* Do not allow the guest to program periodic timers with small
>* interval, since the hrtimers are not throttled by the host
> @@ -1376,10 +1392,6 @@ static void start_sw_period(struct kvm_lapic *apic)
>   }
>   }
>  
> - hrtimer_start(>lapic_timer.timer,
> -   ktime_add_ns(now, apic->lapic_timer.period),
> -   HRTIMER_MODE_ABS_PINNED);
> -
>   apic_debug("%s: bus cycle is %" PRId64 "ns, now 0x%016"
>  PRIx64 ", "
>  "timer initial count 0x%x, period %lldns, "
> @@ -1389,6 +1401,12 @@ static void start_sw_period(struct kvm_lapic *apic)
>  apic->lapic_timer.period,
>  ktime_to_ns(ktime_add_ns(now,
>   apic->lapic_timer.period)));
> +
> + apic->lapic_timer.tscdeadline = kvm_read_l1_tsc(apic->vcpu, tscl) +
> + nsec_to_cycles(apic->vcpu, apic->lapic_timer.period);
> + apic->lapic_timer.target_expiration = ktime_add_ns(now, 
> apic->lapic_timer.period);
> +
> + return true;
>  }
>  
>  bool kvm_lapic_hv_timer_in_use(struct kvm_vcpu *vcpu)
> @@ -1406,22 +1424,12 @@ static void cancel_hv_timer(struct kvm_lapic *apic)
>   apic->lapic_timer.hv_timer_in_use = false;
>  }
>  
> -void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
> -{
> - struct kvm_lapic *apic = vcpu->arch.apic;
> -
> - WARN_ON(!apic->lapic_timer.hv_timer_in_use);
> - WARN_ON(swait_active(>wq));
> - cancel_hv_timer(apic);
> - apic_timer_expired(apic);
> -}
> -EXPORT_SYMBOL_GPL(kvm_lapic_expired_hv_timer);
> -
>  static bool start_hv_timer(struct kvm_lapic *apic)
>  {
>   u64 tscdeadline = apic->lapic_timer.tscdeadline;
>  
> - if (atomic_read(>lapic_timer.pending) ||
> + if ((atomic_read(>lapic_timer.pending) &&
> + !apic_lvtt_period(apic)) ||
>   kvm_x86_ops->set_hv_timer(apic->vcpu, tscdeadline)) {
>   if (apic->lapic_timer.hv_timer_in_use)
>   cancel_hv_timer(apic);
> @@ -1430,7 +1438,8 @@ static bool start_hv_timer(struct kvm_lapic *apic)
>   hrtimer_cancel(>lapic_timer.timer);
>  
>   /* In case the sw timer triggered in the window */
> - if (atomic_read(>lapic_timer.pending))
> + if (atomic_read(>lapic_timer.pending) &&
> + !apic_lvtt_period(apic))
>   cancel_hv_timer(apic);
>   }
>   trace_kvm_hv_timer_state(apic->vcpu->vcpu_id,
> @@ -1438,14 +1447,42 @@ static bool start_hv_timer(struct kvm_lapic *apic)
>   return apic->lapic_timer.hv_timer_in_use;
>  }
>  
> +void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
> +{
> + struct kvm_lapic *apic = vcpu->arch.apic;
> +
> + WARN_ON(!apic->lapic_timer.hv_timer_in_use);
> + WARN_ON(swait_active(>wq));
> + cancel_hv_timer(apic);
> + apic_timer_expired(apic);
> +
> + if (apic_lvtt_period(apic) &&
> + set_target_expiration(apic) &&
> + !start_hv_timer(apic))
> + start_sw_period(apic);
> +}
> +EXPORT_SYMBOL_GPL(kvm_lapic_expired_hv_timer);
> +
>  void kvm_lapic_switch_to_hv_timer(struct kvm_vcpu *vcpu)
>  {
>   struct kvm_lapic *apic = vcpu->arch.apic;
>  
>   WARN_ON(apic->lapic_timer.hv_timer_in_use);
>  
> - if (apic_lvtt_tscdeadline(apic))
> - start_hv_timer(apic);
> + if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic)) {
> + ktime_t remaining, now;
> + u64 tscl = rdtsc();
> +
> + now = apic->lapic_timer.timer.base->get_time();
> + remaining = hrtimer_get_remaining(>lapic_timer.timer);
> + if 

Re: [PATCH 5/5] KVM: LAPIC: add APIC Timer periodic/oneshot mode VMX preemption timer support

[Paolo Bonzini]

On 17/10/2016 09:45, Wanpeng Li wrote:
> + remaining = ktime_sub(apic->lapic_timer.target_expiration, now);
>   if (ktime_to_ns(remaining) < 0)
>   remaining = ktime_set(0, 0);
>  
> @@ -1351,13 +1352,28 @@ static void start_sw_period(struct kvm_lapic *apic)
>  {
>   ktime_t now;
>  
> - /* lapic timer in oneshot or periodic mode */
> + now = apic->lapic_timer.timer.base->get_time();
> +
> + if (likely(ktime_compare(apic->lapic_timer.target_expiration, now)))

ktime_after, not ktime_compare.  Can be fixed on commit, I guess.

Paolo

> + hrtimer_start(>lapic_timer.timer,
> + apic->lapic_timer.target_expiration,
> + HRTIMER_MODE_ABS_PINNED);
> + else
> + apic_timer_expired(apic);
> +}
> +
> +static bool set_target_expiration(struct kvm_lapic *apic)
> +{
> + ktime_t now;
> + u64 tscl = rdtsc();
> +
>   now = apic->lapic_timer.timer.base->get_time();
>   apic->lapic_timer.period = (u64)kvm_lapic_get_reg(apic, APIC_TMICT)
> - * APIC_BUS_CYCLE_NS * apic->divide_count;
> + * APIC_BUS_CYCLE_NS * apic->divide_count;
>  
>   if (!apic->lapic_timer.period)
> - return;
> + return false;
>   /*
>* Do not allow the guest to program periodic timers with small
>* interval, since the hrtimers are not throttled by the host
> @@ -1376,10 +1392,6 @@ static void start_sw_period(struct kvm_lapic *apic)
>   }
>   }
>  
> - hrtimer_start(>lapic_timer.timer,
> -   ktime_add_ns(now, apic->lapic_timer.period),
> -   HRTIMER_MODE_ABS_PINNED);
> -
>   apic_debug("%s: bus cycle is %" PRId64 "ns, now 0x%016"
>  PRIx64 ", "
>  "timer initial count 0x%x, period %lldns, "
> @@ -1389,6 +1401,12 @@ static void start_sw_period(struct kvm_lapic *apic)
>  apic->lapic_timer.period,
>  ktime_to_ns(ktime_add_ns(now,
>   apic->lapic_timer.period)));
> +
> + apic->lapic_timer.tscdeadline = kvm_read_l1_tsc(apic->vcpu, tscl) +
> + nsec_to_cycles(apic->vcpu, apic->lapic_timer.period);
> + apic->lapic_timer.target_expiration = ktime_add_ns(now, 
> apic->lapic_timer.period);
> +
> + return true;
>  }
>  
>  bool kvm_lapic_hv_timer_in_use(struct kvm_vcpu *vcpu)
> @@ -1406,22 +1424,12 @@ static void cancel_hv_timer(struct kvm_lapic *apic)
>   apic->lapic_timer.hv_timer_in_use = false;
>  }
>  
> -void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
> -{
> - struct kvm_lapic *apic = vcpu->arch.apic;
> -
> - WARN_ON(!apic->lapic_timer.hv_timer_in_use);
> - WARN_ON(swait_active(>wq));
> - cancel_hv_timer(apic);
> - apic_timer_expired(apic);
> -}
> -EXPORT_SYMBOL_GPL(kvm_lapic_expired_hv_timer);
> -
>  static bool start_hv_timer(struct kvm_lapic *apic)
>  {
>   u64 tscdeadline = apic->lapic_timer.tscdeadline;
>  
> - if (atomic_read(>lapic_timer.pending) ||
> + if ((atomic_read(>lapic_timer.pending) &&
> + !apic_lvtt_period(apic)) ||
>   kvm_x86_ops->set_hv_timer(apic->vcpu, tscdeadline)) {
>   if (apic->lapic_timer.hv_timer_in_use)
>   cancel_hv_timer(apic);
> @@ -1430,7 +1438,8 @@ static bool start_hv_timer(struct kvm_lapic *apic)
>   hrtimer_cancel(>lapic_timer.timer);
>  
>   /* In case the sw timer triggered in the window */
> - if (atomic_read(>lapic_timer.pending))
> + if (atomic_read(>lapic_timer.pending) &&
> + !apic_lvtt_period(apic))
>   cancel_hv_timer(apic);
>   }
>   trace_kvm_hv_timer_state(apic->vcpu->vcpu_id,
> @@ -1438,14 +1447,42 @@ static bool start_hv_timer(struct kvm_lapic *apic)
>   return apic->lapic_timer.hv_timer_in_use;
>  }
>  
> +void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
> +{
> + struct kvm_lapic *apic = vcpu->arch.apic;
> +
> + WARN_ON(!apic->lapic_timer.hv_timer_in_use);
> + WARN_ON(swait_active(>wq));
> + cancel_hv_timer(apic);
> + apic_timer_expired(apic);
> +
> + if (apic_lvtt_period(apic) &&
> + set_target_expiration(apic) &&
> + !start_hv_timer(apic))
> + start_sw_period(apic);
> +}
> +EXPORT_SYMBOL_GPL(kvm_lapic_expired_hv_timer);
> +
>  void kvm_lapic_switch_to_hv_timer(struct kvm_vcpu *vcpu)
>  {
>   struct kvm_lapic *apic = vcpu->arch.apic;
>  
>   WARN_ON(apic->lapic_timer.hv_timer_in_use);
>  
> - if (apic_lvtt_tscdeadline(apic))
> - start_hv_timer(apic);
> + if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic)) {
> + ktime_t remaining, now;
> + u64 tscl = rdtsc();
> +
> + now = apic->lapic_timer.timer.base->get_time();
> + remaining = hrtimer_get_remaining(>lapic_timer.timer);
> + if 

[PATCH 5/5] KVM: LAPIC: add APIC Timer periodic/oneshot mode VMX preemption timer support

[Wanpeng Li]

From: Wanpeng Li 

Most windows guests still utilize APIC Timer periodic/oneshot mode
instead of tsc-deadline mode, and the APIC Timer periodic/oneshot
mode are still emulated by high overhead hrtimer on host. This patch
converts the expected expire time of the periodic/oneshot mode to
guest deadline tsc in order to leverage VMX preemption timer logic
for APIC Timer tsc-deadline mode. After each preemption timer vmexit
preemption timer is restarted to emulate LVTT current-count register
is automatically reloaded from the initial-count register when the
count reaches 0. This patch reduces ~3800 cycles for each APIC Timer
periodic mode operation virtualization.

Cc: Paolo Bonzini 
Cc: Radim Krčmář 
Cc: Yunhong Jiang 
Signed-off-by: Wanpeng Li 
---
 arch/x86/kvm/lapic.c | 103 ---
 arch/x86/kvm/lapic.h |   1 +
 2 files changed, 75 insertions(+), 29 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 0354a79..4e77d37 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1090,7 +1090,7 @@ static void apic_send_ipi(struct kvm_lapic *apic)
 
 static u32 apic_get_tmcct(struct kvm_lapic *apic)
 {
-   ktime_t remaining;
+   ktime_t remaining, now;
s64 ns;
u32 tmcct;
 
@@ -1101,7 +1101,8 @@ static u32 apic_get_tmcct(struct kvm_lapic *apic)
apic->lapic_timer.period == 0)
return 0;
 
-   remaining = hrtimer_get_remaining(>lapic_timer.timer);
+   now = apic->lapic_timer.timer.base->get_time();
+   remaining = ktime_sub(apic->lapic_timer.target_expiration, now);
if (ktime_to_ns(remaining) < 0)
remaining = ktime_set(0, 0);
 
@@ -1351,13 +1352,28 @@ static void start_sw_period(struct kvm_lapic *apic)
 {
ktime_t now;
 
-   /* lapic timer in oneshot or periodic mode */
+   now = apic->lapic_timer.timer.base->get_time();
+
+   if (likely(ktime_compare(apic->lapic_timer.target_expiration, now)))
+   hrtimer_start(>lapic_timer.timer,
+   apic->lapic_timer.target_expiration,
+   HRTIMER_MODE_ABS_PINNED);
+   else
+   apic_timer_expired(apic);
+}
+
+static bool set_target_expiration(struct kvm_lapic *apic)
+{
+   ktime_t now;
+   u64 tscl = rdtsc();
+
now = apic->lapic_timer.timer.base->get_time();
apic->lapic_timer.period = (u64)kvm_lapic_get_reg(apic, APIC_TMICT)
-   * APIC_BUS_CYCLE_NS * apic->divide_count;
+   * APIC_BUS_CYCLE_NS * apic->divide_count;
 
if (!apic->lapic_timer.period)
-   return;
+   return false;
+
/*
 * Do not allow the guest to program periodic timers with small
 * interval, since the hrtimers are not throttled by the host
@@ -1376,10 +1392,6 @@ static void start_sw_period(struct kvm_lapic *apic)
}
}
 
-   hrtimer_start(>lapic_timer.timer,
- ktime_add_ns(now, apic->lapic_timer.period),
- HRTIMER_MODE_ABS_PINNED);
-
apic_debug("%s: bus cycle is %" PRId64 "ns, now 0x%016"
   PRIx64 ", "
   "timer initial count 0x%x, period %lldns, "
@@ -1389,6 +1401,12 @@ static void start_sw_period(struct kvm_lapic *apic)
   apic->lapic_timer.period,
   ktime_to_ns(ktime_add_ns(now,
apic->lapic_timer.period)));
+
+   apic->lapic_timer.tscdeadline = kvm_read_l1_tsc(apic->vcpu, tscl) +
+   nsec_to_cycles(apic->vcpu, apic->lapic_timer.period);
+   apic->lapic_timer.target_expiration = ktime_add_ns(now, 
apic->lapic_timer.period);
+
+   return true;
 }
 
 bool kvm_lapic_hv_timer_in_use(struct kvm_vcpu *vcpu)
@@ -1406,22 +1424,12 @@ static void cancel_hv_timer(struct kvm_lapic *apic)
apic->lapic_timer.hv_timer_in_use = false;
 }
 
-void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
-{
-   struct kvm_lapic *apic = vcpu->arch.apic;
-
-   WARN_ON(!apic->lapic_timer.hv_timer_in_use);
-   WARN_ON(swait_active(>wq));
-   cancel_hv_timer(apic);
-   apic_timer_expired(apic);
-}
-EXPORT_SYMBOL_GPL(kvm_lapic_expired_hv_timer);
-
 static bool start_hv_timer(struct kvm_lapic *apic)
 {
u64 tscdeadline = apic->lapic_timer.tscdeadline;
 
-   if (atomic_read(>lapic_timer.pending) ||
+   if ((atomic_read(>lapic_timer.pending) &&
+   !apic_lvtt_period(apic)) ||
kvm_x86_ops->set_hv_timer(apic->vcpu, tscdeadline)) {
if (apic->lapic_timer.hv_timer_in_use)
cancel_hv_timer(apic);
@@ -1430,7 +1438,8 @@ static bool start_hv_timer(struct kvm_lapic *apic)
hrtimer_cancel(>lapic_timer.timer);
 
/* In case the sw timer triggered in the window */

[PATCH 5/5] KVM: LAPIC: add APIC Timer periodic/oneshot mode VMX preemption timer support

[Wanpeng Li]

From: Wanpeng Li 

Most windows guests still utilize APIC Timer periodic/oneshot mode
instead of tsc-deadline mode, and the APIC Timer periodic/oneshot
mode are still emulated by high overhead hrtimer on host. This patch
converts the expected expire time of the periodic/oneshot mode to
guest deadline tsc in order to leverage VMX preemption timer logic
for APIC Timer tsc-deadline mode. After each preemption timer vmexit
preemption timer is restarted to emulate LVTT current-count register
is automatically reloaded from the initial-count register when the
count reaches 0. This patch reduces ~3800 cycles for each APIC Timer
periodic mode operation virtualization.

Cc: Paolo Bonzini 
Cc: Radim Krčmář 
Cc: Yunhong Jiang 
Signed-off-by: Wanpeng Li 
---
 arch/x86/kvm/lapic.c | 103 ---
 arch/x86/kvm/lapic.h |   1 +
 2 files changed, 75 insertions(+), 29 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 0354a79..4e77d37 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1090,7 +1090,7 @@ static void apic_send_ipi(struct kvm_lapic *apic)
 
 static u32 apic_get_tmcct(struct kvm_lapic *apic)
 {
-   ktime_t remaining;
+   ktime_t remaining, now;
s64 ns;
u32 tmcct;
 
@@ -1101,7 +1101,8 @@ static u32 apic_get_tmcct(struct kvm_lapic *apic)
apic->lapic_timer.period == 0)
return 0;
 
-   remaining = hrtimer_get_remaining(>lapic_timer.timer);
+   now = apic->lapic_timer.timer.base->get_time();
+   remaining = ktime_sub(apic->lapic_timer.target_expiration, now);
if (ktime_to_ns(remaining) < 0)
remaining = ktime_set(0, 0);
 
@@ -1351,13 +1352,28 @@ static void start_sw_period(struct kvm_lapic *apic)
 {
ktime_t now;
 
-   /* lapic timer in oneshot or periodic mode */
+   now = apic->lapic_timer.timer.base->get_time();
+
+   if (likely(ktime_compare(apic->lapic_timer.target_expiration, now)))
+   hrtimer_start(>lapic_timer.timer,
+   apic->lapic_timer.target_expiration,
+   HRTIMER_MODE_ABS_PINNED);
+   else
+   apic_timer_expired(apic);
+}
+
+static bool set_target_expiration(struct kvm_lapic *apic)
+{
+   ktime_t now;
+   u64 tscl = rdtsc();
+
now = apic->lapic_timer.timer.base->get_time();
apic->lapic_timer.period = (u64)kvm_lapic_get_reg(apic, APIC_TMICT)
-   * APIC_BUS_CYCLE_NS * apic->divide_count;
+   * APIC_BUS_CYCLE_NS * apic->divide_count;
 
if (!apic->lapic_timer.period)
-   return;
+   return false;
+
/*
 * Do not allow the guest to program periodic timers with small
 * interval, since the hrtimers are not throttled by the host
@@ -1376,10 +1392,6 @@ static void start_sw_period(struct kvm_lapic *apic)
}
}
 
-   hrtimer_start(>lapic_timer.timer,
- ktime_add_ns(now, apic->lapic_timer.period),
- HRTIMER_MODE_ABS_PINNED);
-
apic_debug("%s: bus cycle is %" PRId64 "ns, now 0x%016"
   PRIx64 ", "
   "timer initial count 0x%x, period %lldns, "
@@ -1389,6 +1401,12 @@ static void start_sw_period(struct kvm_lapic *apic)
   apic->lapic_timer.period,
   ktime_to_ns(ktime_add_ns(now,
apic->lapic_timer.period)));
+
+   apic->lapic_timer.tscdeadline = kvm_read_l1_tsc(apic->vcpu, tscl) +
+   nsec_to_cycles(apic->vcpu, apic->lapic_timer.period);
+   apic->lapic_timer.target_expiration = ktime_add_ns(now, 
apic->lapic_timer.period);
+
+   return true;
 }
 
 bool kvm_lapic_hv_timer_in_use(struct kvm_vcpu *vcpu)
@@ -1406,22 +1424,12 @@ static void cancel_hv_timer(struct kvm_lapic *apic)
apic->lapic_timer.hv_timer_in_use = false;
 }
 
-void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
-{
-   struct kvm_lapic *apic = vcpu->arch.apic;
-
-   WARN_ON(!apic->lapic_timer.hv_timer_in_use);
-   WARN_ON(swait_active(>wq));
-   cancel_hv_timer(apic);
-   apic_timer_expired(apic);
-}
-EXPORT_SYMBOL_GPL(kvm_lapic_expired_hv_timer);
-
 static bool start_hv_timer(struct kvm_lapic *apic)
 {
u64 tscdeadline = apic->lapic_timer.tscdeadline;
 
-   if (atomic_read(>lapic_timer.pending) ||
+   if ((atomic_read(>lapic_timer.pending) &&
+   !apic_lvtt_period(apic)) ||
kvm_x86_ops->set_hv_timer(apic->vcpu, tscdeadline)) {
if (apic->lapic_timer.hv_timer_in_use)
cancel_hv_timer(apic);
@@ -1430,7 +1438,8 @@ static bool start_hv_timer(struct kvm_lapic *apic)
hrtimer_cancel(>lapic_timer.timer);
 
/* In case the sw timer triggered in the window */
-   if (atomic_read(>lapic_timer.pending))
+   if (atomic_read(>lapic_timer.pending) &&
+