[PATCH v2 7/8] arm/arm64: KVM: Rework the arch timer to use level-triggered semantics
Christoffer Dall
christoffer.dall at linaro.org
Mon Sep 14 04:48:02 PDT 2015
On Mon, Sep 14, 2015 at 11:29:53AM +0200, Eric Auger wrote:
> On 09/04/2015 09:40 PM, Christoffer Dall wrote:
> > The arch timer currently uses edge-triggered semantics in the sense that
> > the line is never sampled by the vgic and lowering the line from the
> > timer to the vgic doesn't have any affect on the pending state of
> s/affect/effect
> > virtual interrupts in the vgic. This means that we do not support a
> > guest with the otherwise valid behavior of (1) disable interrupts (2)
> > enable the timer (3) disable the timer (4) enable interrupts. Such a
> > guest would validly not expect to see any interrupts on real hardware,
> > but will see interrupts on KVM.
> >
> > This patches fixes this shortcoming through the following series of
> > changes.
> >
> > First, we change the flow of the timer/vgic sync/flush operations. Now
> > the timer is always flushed/synced before the vgic,
> for the flush it was already the case
> because the vgic
> > samples the state of the timer output. This has the implication that we
> > move the timer operations in to non-preempible sections, but that is
> > fine after the previous commit getting rid of hrtimer schedules on every
> > entry/exit.
> >
> > Second, we change the internal behavior of the timer, letting the timer
> > keep track of its previous output state, and only lower/raise the line
> > to the vgic when the state changes. Note that in theory this could have
> > been accomplished more simply by signalling the vgic every time the
> > state *potentially* changed, but we don't want to be hitting the vgic
> > more often than necessary.
> >
> > Third, we get rid of the use of the map->active field in the vgic and
> > instead simply set the interrupt as active on the physical distributor
> > whenever we signal a mapped interrupt to the guest, and we reset the
> > active state when we sync back the HW state from the vgic.
> >
> > Fourth, and finally, we now initialize the timer PPIs (and all the other
> > unused PPIs for now), to be level-triggered, and modify the sync code to
> > sample the line state on HW sync and re-inject a new interrupt if it is
> > still pending at that time.
> >
> > Signed-off-by: Christoffer Dall <christoffer.dall at linaro.org>
> > ---
> > arch/arm/kvm/arm.c | 11 ++++++--
> > include/kvm/arm_arch_timer.h | 2 +-
> > include/kvm/arm_vgic.h | 3 --
> > virt/kvm/arm/arch_timer.c | 65 +++++++++++++++++++++++++++++-------------
> > virt/kvm/arm/vgic.c | 67 +++++++++++++++-----------------------------
> > 5 files changed, 78 insertions(+), 70 deletions(-)
> >
> > diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> > index bdf8871..102a4aa 100644
> > --- a/arch/arm/kvm/arm.c
> > +++ b/arch/arm/kvm/arm.c
> > @@ -561,9 +561,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
> >
> > if (ret <= 0 || need_new_vmid_gen(vcpu->kvm)) {
> > local_irq_enable();
> > + kvm_timer_sync_hwstate(vcpu);
> > kvm_vgic_sync_hwstate(vcpu);
> > preempt_enable();
> > - kvm_timer_sync_hwstate(vcpu);
> > continue;
> > }
> >
> > @@ -608,12 +608,17 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
> > kvm_guest_exit();
> > trace_kvm_exit(kvm_vcpu_trap_get_class(vcpu), *vcpu_pc(vcpu));
> >
> > + /*
> > + * We must sync the timer state before the vgic state so that
> > + * the vgic can properly sample the updated state of the
> > + * interrupt line.
> > + */
> > + kvm_timer_sync_hwstate(vcpu);
> > +
> > kvm_vgic_sync_hwstate(vcpu);
> >
> > preempt_enable();
> >
> > - kvm_timer_sync_hwstate(vcpu);
> > -
> > ret = handle_exit(vcpu, run, ret);
> > }
> >
> > diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h
> > index ef14cc1..1800227 100644
> > --- a/include/kvm/arm_arch_timer.h
> > +++ b/include/kvm/arm_arch_timer.h
> > @@ -51,7 +51,7 @@ struct arch_timer_cpu {
> > bool armed;
> >
> > /* Timer IRQ */
> > - const struct kvm_irq_level *irq;
> > + struct kvm_irq_level irq;
> >
> > /* VGIC mapping */
> > struct irq_phys_map *map;
> > diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
> > index d901f1a..99011a0 100644
> > --- a/include/kvm/arm_vgic.h
> > +++ b/include/kvm/arm_vgic.h
> > @@ -163,7 +163,6 @@ struct irq_phys_map {
> > u32 virt_irq;
> > u32 phys_irq;
> > u32 irq;
> > - bool active;
> > };
> >
> > struct irq_phys_map_entry {
> > @@ -358,8 +357,6 @@ int kvm_vgic_vcpu_active_irq(struct kvm_vcpu *vcpu);
> > struct irq_phys_map *kvm_vgic_map_phys_irq(struct kvm_vcpu *vcpu,
> > int virt_irq, int irq);
> > int kvm_vgic_unmap_phys_irq(struct kvm_vcpu *vcpu, struct irq_phys_map *map);
> > -bool kvm_vgic_get_phys_irq_active(struct irq_phys_map *map);
> > -void kvm_vgic_set_phys_irq_active(struct irq_phys_map *map, bool active);
> >
> > #define irqchip_in_kernel(k) (!!((k)->arch.vgic.in_kernel))
> > #define vgic_initialized(k) (!!((k)->arch.vgic.nr_cpus))
> > diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
> > index 7991537..0cdd092 100644
> > --- a/virt/kvm/arm/arch_timer.c
> > +++ b/virt/kvm/arm/arch_timer.c
> > @@ -59,18 +59,6 @@ static void timer_disarm(struct arch_timer_cpu *timer)
> > }
> > }
> >
> > -static void kvm_timer_inject_irq(struct kvm_vcpu *vcpu)
> > -{
> > - int ret;
> > - struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> > -
> > - kvm_vgic_set_phys_irq_active(timer->map, true);
> > - ret = kvm_vgic_inject_mapped_irq(vcpu->kvm, vcpu->vcpu_id,
> > - timer->map,
> > - timer->irq->level);
> > - WARN_ON(ret);
> > -}
> > -
> > static irqreturn_t kvm_arch_timer_handler(int irq, void *dev_id)
> > {
> > struct kvm_vcpu *vcpu = *(struct kvm_vcpu **)dev_id;
> > @@ -116,8 +104,7 @@ static bool kvm_timer_irq_can_fire(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);
> > + (timer->cntv_ctl & ARCH_TIMER_CTRL_ENABLE);
> > }
> >
> > bool kvm_timer_should_fire(struct kvm_vcpu *vcpu)
> > @@ -134,6 +121,41 @@ bool kvm_timer_should_fire(struct kvm_vcpu *vcpu)
> > return cval <= now;
> > }
> >
> > +static void kvm_timer_update_irq(struct kvm_vcpu *vcpu, bool new_level)
> > +{
> > + int ret;
> > + struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> > +
> > + BUG_ON(!vgic_initialized(vcpu->kvm));
> > +
> > + timer->irq.level = new_level;
> > + ret = kvm_vgic_inject_mapped_irq(vcpu->kvm, vcpu->vcpu_id,
> > + timer->map,
> > + timer->irq.level);
> > + WARN_ON(ret);
> > +}
> > +
> > +/*
> > + * Check if there was a change in the timer state (should we raise or lower
> > + * the line level to the GIC).
> > + */
> > +static void kvm_timer_update_state(struct kvm_vcpu *vcpu)
> > +{
> > + struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> > +
> > + /*
> > + * If userspace modified the timer registers via SET_ONE_REG before
> > + * the vgic was initialized, we mustn't set the timer->irq.level value
> > + * because the guest would never see the interrupt. Instead wait
> > + * until we call this funciton from kvm_timer_flush_hwstate.
> s/funciton/function
> > + */
> > + if (!vgic_initialized(vcpu->kvm))
> > + return;
> > +
> > + if (kvm_timer_should_fire(vcpu) != timer->irq.level)
> > + kvm_timer_update_irq(vcpu, !timer->irq.level);
> > +}
> > +
> > /*
> > * 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
> > @@ -193,8 +215,7 @@ 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.
> > */
> > - if (kvm_timer_should_fire(vcpu))
> > - kvm_timer_inject_irq(vcpu);
> > + kvm_timer_update_state(vcpu);
> > }
> >
> > /**
> > @@ -210,8 +231,11 @@ void kvm_timer_sync_hwstate(struct kvm_vcpu *vcpu)
> >
> > BUG_ON(timer_is_armed(timer));
> >
> > - if (kvm_timer_should_fire(vcpu))
> > - kvm_timer_inject_irq(vcpu);
> > + /*
> > + * The guest could have modified the timer registers or the timer
> > + * could have expired, update the timer state.
> > + */
> > + kvm_timer_update_state(vcpu);
> > }
> >
> > int kvm_timer_vcpu_reset(struct kvm_vcpu *vcpu,
> > @@ -226,7 +250,7 @@ int kvm_timer_vcpu_reset(struct kvm_vcpu *vcpu,
> > * kvm_vcpu_set_target(). To handle this, we determine
> > * vcpu timer irq number when the vcpu is reset.
> > */
> > - timer->irq = irq;
> > + timer->irq.irq = irq->irq;
> >
> > /*
> > * The bits in CNTV_CTL are architecturally reset to UNKNOWN for ARMv8
> > @@ -235,6 +259,7 @@ int kvm_timer_vcpu_reset(struct kvm_vcpu *vcpu,
> > * the ARMv7 architecture.
> > */
> > timer->cntv_ctl = 0;
> > + kvm_timer_update_state(vcpu);
> >
> > /*
> > * Tell the VGIC that the virtual interrupt is tied to a
> > @@ -279,6 +304,8 @@ int kvm_arm_timer_set_reg(struct kvm_vcpu *vcpu, u64 regid, u64 value)
> > default:
> > return -1;
> > }
> > +
> > + kvm_timer_update_state(vcpu);
> > return 0;
> > }
> >
> > diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> > index 9ed8d53..f4ea950 100644
> > --- a/virt/kvm/arm/vgic.c
> > +++ b/virt/kvm/arm/vgic.c
> > @@ -1422,34 +1422,43 @@ static bool vgic_process_maintenance(struct kvm_vcpu *vcpu)
> > /*
> > * Save the physical active state, and reset it to inactive.
> > *
> > - * Return 1 if HW interrupt went from active to inactive, and 0 otherwise.
> > + * Return true if there's a pending level triggered interrupt line to queue.
> > */
> > -static int vgic_sync_hwirq(struct kvm_vcpu *vcpu, struct vgic_lr vlr)
> > +static bool vgic_sync_hwirq(struct kvm_vcpu *vcpu, int lr, struct vgic_lr vlr)
> > {
> > struct irq_phys_map *map;
> > + bool phys_active;
> > int ret;
> >
> > if (!(vlr.state & LR_HW))
> > return 0;
> >
> > map = vgic_irq_map_search(vcpu, vlr.irq);
> > - BUG_ON(!map || !map->active);
> > + BUG_ON(!map);
> >
> > ret = irq_get_irqchip_state(map->irq,
> > IRQCHIP_STATE_ACTIVE,
> > - &map->active);
> > + &phys_active);
> >
> > WARN_ON(ret);
> >
> > - if (map->active) {
> > + if (phys_active) {
> > + /*
> > + * Interrupt still marked as active on the physical
> > + * distributor, so guest did not EOI it yet. Reset to
> > + * non-active so that other VMs can see interrupts from this
> > + * device.
> > + */
> > ret = irq_set_irqchip_state(map->irq,
> > IRQCHIP_STATE_ACTIVE,
> > false);
> > WARN_ON(ret);
> > - return 0;
> > + return false;
> > }
> >
> > - return 1;
> > + /* Mapped edge-triggered interrupts not yet supported. */
> > + WARN_ON(vgic_irq_is_edge(vcpu, vlr.irq));
> > + return process_level_irq(vcpu, lr, vlr);
> > }
> >
> > /* Sync back the VGIC state after a guest run */
> > @@ -1474,18 +1483,8 @@ static void __kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu)
> > continue;
> >
> > vlr = vgic_get_lr(vcpu, lr);
> > - if (vgic_sync_hwirq(vcpu, vlr)) {
> > - /*
> > - * So this is a HW interrupt that the guest
> > - * EOI-ed. Clean the LR state and allow the
> > - * interrupt to be sampled again.
> > - */
> > - vlr.state = 0;
> > - vlr.hwirq = 0;
> > - vgic_set_lr(vcpu, lr, vlr);
> > - vgic_irq_clear_queued(vcpu, vlr.irq);
> > - set_bit(lr, elrsr_ptr);
> > - }
> > + if (vgic_sync_hwirq(vcpu, lr, vlr))
> > + level_pending = true;
> >
> > if (!test_bit(lr, elrsr_ptr))
> > continue;
> > @@ -1861,30 +1860,6 @@ static void vgic_free_phys_irq_map_rcu(struct rcu_head *rcu)
> > }
> >
> > /**
> > - * kvm_vgic_get_phys_irq_active - Return the active state of a mapped IRQ
> > - *
> > - * Return the logical active state of a mapped interrupt. This doesn't
> > - * necessarily reflects the current HW state.
> > - */
> > -bool kvm_vgic_get_phys_irq_active(struct irq_phys_map *map)
> > -{
> > - BUG_ON(!map);
> > - return map->active;
> > -}
> > -
> > -/**
> > - * kvm_vgic_set_phys_irq_active - Set the active state of a mapped IRQ
> > - *
> > - * Set the logical active state of a mapped interrupt. This doesn't
> > - * immediately affects the HW state.
> > - */
> > -void kvm_vgic_set_phys_irq_active(struct irq_phys_map *map, bool active)
> > -{
> > - BUG_ON(!map);
> > - map->active = active;
> > -}
> > -
> > -/**
> > * kvm_vgic_unmap_phys_irq - Remove a virtual to physical IRQ mapping
> > * @vcpu: The VCPU pointer
> > * @map: The pointer to a mapping obtained through kvm_vgic_map_phys_irq
> > @@ -2112,10 +2087,14 @@ int vgic_init(struct kvm *kvm)
> > if (i < VGIC_NR_SGIS)
> > vgic_bitmap_set_irq_val(&dist->irq_enabled,
> > vcpu->vcpu_id, i, 1);
> > - if (i < VGIC_NR_PRIVATE_IRQS)
> > + if (i < VGIC_NR_SGIS)
> > vgic_bitmap_set_irq_val(&dist->irq_cfg,
> > vcpu->vcpu_id, i,
> > VGIC_CFG_EDGE);
> > + else if (i < VGIC_NR_PRIVATE_IRQS) /* PPIs */
> > + vgic_bitmap_set_irq_val(&dist->irq_cfg,
> > + vcpu->vcpu_id, i,
> > + VGIC_CFG_LEVEL);
> nit: use the same if block for enable & cfg?
sure.
Thanks,
-Christoffer
> > }
> >
> > vgic_enable(vcpu);
> >
>
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