On 30/08/15 14:54, Christoffer Dall wrote:
> We currently schedule a soft timer every time we exit the guest if the
> timer did not expire while running the guest. This is really not
> necessary, because the only work we do in the timer work function is to
> kick the vcpu.
>
> Kicking the vcpu does two things:
> (1) If the vpcu thread is on a waitqueue, make it runnable and remove it
> from the waitqueue.
> (2) If the vcpu is running on a different physical CPU from the one
> doing the kick, it sends a reschedule IPI.
>
> The second case cannot happen, because the soft timer is only ever
> scheduled when the vcpu is not running. The first case is only relevant
> when the vcpu thread is on a waitqueue, which is only the case when the
> vcpu thread has called kvm_vcpu_block().
>
> Therefore, we only need to make sure a timer is scheduled for
> kvm_vcpu_block(), which we do by encapsulating all calls to
> kvm_vcpu_block() with kvm_timer_{un}schedule calls.
>
> Additionally, we only schedule a soft timer if the timer is enabled and
> unmasked, since it is useless otherwise.
>
> Note that theoretically userspace can use the SET_ONE_REG interface to
> change registers that should cause the timer to fire, even if the vcpu
> is blocked without a scheduled timer, but this case was not supported
> before this patch and we leave it for future work for now.
>
> Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
> ---
> arch/arm/include/asm/kvm_host.h | 3 --
> arch/arm/kvm/arm.c | 10 +++++
> arch/arm64/include/asm/kvm_host.h | 3 --
> include/kvm/arm_arch_timer.h | 2 +
> virt/kvm/arm/arch_timer.c | 89 +++++++++++++++++++++++++--------------
> 5 files changed, 70 insertions(+), 37 deletions(-)
>
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index 86fcf6e..dcba0fa 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -236,7 +236,4 @@ static inline void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) {}
> static inline void kvm_arm_clear_debug(struct kvm_vcpu *vcpu) {}
> static inline void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu) {}
>
> -static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {}
> -static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}
> -
> #endif /* __ARM_KVM_HOST_H__ */
> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> index ce404a5..bdf8871 100644
> --- a/arch/arm/kvm/arm.c
> +++ b/arch/arm/kvm/arm.c
> @@ -271,6 +271,16 @@ int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu)
> return kvm_timer_should_fire(vcpu);
> }
>
> +void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu)
> +{
> + kvm_timer_schedule(vcpu);
> +}
> +
> +void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu)
> +{
> + kvm_timer_unschedule(vcpu);
> +}
> +
> int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
> {
> /* Force users to call KVM_ARM_VCPU_INIT */
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index dd143f5..415938d 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -257,7 +257,4 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu);
> void kvm_arm_clear_debug(struct kvm_vcpu *vcpu);
> void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu);
>
> -static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {}
> -static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}
> -
> #endif /* __ARM64_KVM_HOST_H__ */
> diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h
> index e1e4d7c..ef14cc1 100644
> --- a/include/kvm/arm_arch_timer.h
> +++ b/include/kvm/arm_arch_timer.h
> @@ -71,5 +71,7 @@ u64 kvm_arm_timer_get_reg(struct kvm_vcpu *, u64 regid);
> int kvm_arm_timer_set_reg(struct kvm_vcpu *, u64 regid, u64 value);
>
> bool kvm_timer_should_fire(struct kvm_vcpu *vcpu);
> +void kvm_timer_schedule(struct kvm_vcpu *vcpu);
> +void kvm_timer_unschedule(struct kvm_vcpu *vcpu);
>
> #endif
> diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
> index 76e38d2..018f3d6 100644
> --- a/virt/kvm/arm/arch_timer.c
> +++ b/virt/kvm/arm/arch_timer.c
> @@ -111,14 +111,21 @@ static enum hrtimer_restart kvm_timer_expire(struct hrtimer *hrt)
> return HRTIMER_NORESTART;
> }
>
> +static bool kvm_timer_irq_enabled(struct kvm_vcpu *vcpu)
> +{
> + struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> +
> + return !(timer->cntv_ctl & ARCH_TIMER_CTRL_IT_MASK) &&
> + (timer->cntv_ctl & ARCH_TIMER_CTRL_ENABLE) &&
> + !kvm_vgic_get_phys_irq_active(timer->map);
> +}
Nit: To me, this is not a predicate for "IRQ enabled", but "IRQ can
fire" instead, which seems to complement the kvm_timer_should_fire just
below.
> +
> bool kvm_timer_should_fire(struct kvm_vcpu *vcpu)
> {
> struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> cycle_t cval, now;
>
> - if ((timer->cntv_ctl & ARCH_TIMER_CTRL_IT_MASK) ||
> - !(timer->cntv_ctl & ARCH_TIMER_CTRL_ENABLE) ||
> - kvm_vgic_get_phys_irq_active(timer->map))
> + if (!kvm_timer_irq_enabled(vcpu))
> return false;
>
> cval = timer->cntv_cval;
> @@ -127,24 +134,59 @@ bool kvm_timer_should_fire(struct kvm_vcpu *vcpu)
> return cval <= now;
> }
>
> -/**
> - * kvm_timer_flush_hwstate - prepare to move the virt timer to the cpu
> - * @vcpu: The vcpu pointer
> - *
> - * Disarm any pending soft timers, since the world-switch code will write the
> - * virtual timer state back to the physical CPU.
> +/*
> + * Schedule the background timer before calling kvm_vcpu_block, so that this
> + * thread is removed from its waitqueue and made runnable when there's a timer
> + * interrupt to handle.
> */
> -void kvm_timer_flush_hwstate(struct kvm_vcpu *vcpu)
> +void kvm_timer_schedule(struct kvm_vcpu *vcpu)
> {
> struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> + u64 ns;
> + cycle_t cval, now;
> +
> + /*
> + * No need to schedule a background timer if the guest timer has
> + * already expired, because kvm_vcpu_block will return before putting
> + * the thread to sleep.
> + */
> + if (kvm_timer_should_fire(vcpu))
> + return;
>
> /*
> - * We're about to run this vcpu again, so there is no need to
> - * keep the background timer running, as we're about to
> - * populate the CPU timer again.
> + * If the timer is either not capable of raising interrupts (disabled
> + * or masked) or if we already have a background timer, then there's
> + * no more work for us to do.
> */
> + if (!kvm_timer_irq_enabled(vcpu) || timer_is_armed(timer))
> + return;
Do we need to retest kvm_timer_irq_enabled here? It is already implied
by kvm_timer_should_fire...
> +
> + /* The timer has not yet expired, schedule a background timer */
> + cval = timer->cntv_cval;
> + now = kvm_phys_timer_read() - vcpu->kvm->arch.timer.cntvoff;
> +
> + ns = cyclecounter_cyc2ns(timecounter->cc,
> + cval - now,
> + timecounter->mask,
> + &timecounter->frac);
> + timer_arm(timer, ns);
> +}
> +
> +void kvm_timer_unschedule(struct kvm_vcpu *vcpu)
> +{
> + struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> timer_disarm(timer);
> +}
>
> +/**
> + * kvm_timer_flush_hwstate - prepare to move the virt timer to the cpu
> + * @vcpu: The vcpu pointer
> + *
> + * Check if the virtual timer has expired while we were running in the host,
> + * and inject an interrupt if that was the case.
> + */
> +void kvm_timer_flush_hwstate(struct kvm_vcpu *vcpu)
> +{
> /*
> * If the timer expired while we were not scheduled, now is the time
> * to inject it.
> @@ -157,32 +199,17 @@ void kvm_timer_flush_hwstate(struct kvm_vcpu *vcpu)
> * kvm_timer_sync_hwstate - sync timer state from cpu
> * @vcpu: The vcpu pointer
> *
> - * Check if the virtual timer was armed and either schedule a corresponding
> - * soft timer or inject directly if already expired.
> + * Check if the virtual timer has expired while we werer running in the guest,
s/werer/were/
> + * and inject an interrupt if that was the case.
> */
> void kvm_timer_sync_hwstate(struct kvm_vcpu *vcpu)
> {
> struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> - cycle_t cval, now;
> - u64 ns;
>
> BUG_ON(timer_is_armed(timer));
>
> - if (kvm_timer_should_fire(vcpu)) {
> - /*
> - * Timer has already expired while we were not
> - * looking. Inject the interrupt and carry on.
> - */
> + if (kvm_timer_should_fire(vcpu))
> kvm_timer_inject_irq(vcpu);
> - return;
> - }
> -
> - cval = timer->cntv_cval;
> - now = kvm_phys_timer_read() - vcpu->kvm->arch.timer.cntvoff;
> -
> - ns = cyclecounter_cyc2ns(timecounter->cc, cval - now, timecounter->mask,
> - &timecounter->frac);
> - timer_arm(timer, ns);
> }
>
> int kvm_timer_vcpu_reset(struct kvm_vcpu *vcpu,
>
Apart from the few comments above, looks pretty good.
M.
--
Jazz is not dead. It just smells funny...
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