Instead of calling into kvm_timer_[un]schedule from the main kvm blocking path, test if the VCPU is on the wait queue from the load/put path and perform the background timer setup/cancel in this path.
This has the distinct advantage that we no longer race between load/put and schedule/unschedule and programming and canceling of the bg_timer always happens when the timer state is not loaded. Note that we must now remove the checks in kvm_timer_blocking that do not schedule a background timer if one of the timers can fire, because we no longer have a guarantee that kvm_vcpu_check_block() will be called before kvm_timer_blocking. Reported-by: Andre Przywara <andre.przyw...@arm.com> Signed-off-by: Christoffer Dall <christoffer.d...@arm.com> Signed-off-by: Marc Zyngier <marc.zyng...@arm.com> --- include/kvm/arm_arch_timer.h | 3 --- virt/kvm/arm/arch_timer.c | 35 ++++++++++++++--------------------- virt/kvm/arm/arm.c | 2 -- 3 files changed, 14 insertions(+), 26 deletions(-) diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h index 33771352dcd6..d6e6a45d1d24 100644 --- a/include/kvm/arm_arch_timer.h +++ b/include/kvm/arm_arch_timer.h @@ -76,9 +76,6 @@ int kvm_arm_timer_has_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr); bool kvm_timer_is_pending(struct kvm_vcpu *vcpu); -void kvm_timer_schedule(struct kvm_vcpu *vcpu); -void kvm_timer_unschedule(struct kvm_vcpu *vcpu); - u64 kvm_phys_timer_read(void); void kvm_timer_vcpu_load(struct kvm_vcpu *vcpu); diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c index b07ac4614e1c..4986028d9829 100644 --- a/virt/kvm/arm/arch_timer.c +++ b/virt/kvm/arm/arch_timer.c @@ -349,22 +349,12 @@ static void vtimer_save_state(struct kvm_vcpu *vcpu) * thread is removed from its waitqueue and made runnable when there's a timer * interrupt to handle. */ -void kvm_timer_schedule(struct kvm_vcpu *vcpu) +static void kvm_timer_blocking(struct kvm_vcpu *vcpu) { struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu; struct arch_timer_context *vtimer = vcpu_vtimer(vcpu); struct arch_timer_context *ptimer = vcpu_ptimer(vcpu); - vtimer_save_state(vcpu); - - /* - * No need to schedule a background timer if any guest timer has - * already expired, because kvm_vcpu_block will return before putting - * the thread to sleep. - */ - if (kvm_timer_should_fire(vtimer) || kvm_timer_should_fire(ptimer)) - return; - /* * If both timers are not capable of raising interrupts (disabled or * masked), then there's no more work for us to do. @@ -373,12 +363,19 @@ void kvm_timer_schedule(struct kvm_vcpu *vcpu) return; /* - * The guest timers have not yet expired, schedule a background timer. + * At least one guest time will expire. Schedule a background timer. * Set the earliest expiration time among the guest timers. */ soft_timer_start(&timer->bg_timer, kvm_timer_earliest_exp(vcpu)); } +static void kvm_timer_unblocking(struct kvm_vcpu *vcpu) +{ + struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu; + + soft_timer_cancel(&timer->bg_timer); +} + static void vtimer_restore_state(struct kvm_vcpu *vcpu) { struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu; @@ -401,15 +398,6 @@ static void vtimer_restore_state(struct kvm_vcpu *vcpu) local_irq_restore(flags); } -void kvm_timer_unschedule(struct kvm_vcpu *vcpu) -{ - struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu; - - vtimer_restore_state(vcpu); - - soft_timer_cancel(&timer->bg_timer); -} - static void set_cntvoff(u64 cntvoff) { u32 low = lower_32_bits(cntvoff); @@ -485,6 +473,8 @@ void kvm_timer_vcpu_load(struct kvm_vcpu *vcpu) /* Set the background timer for the physical timer emulation. */ phys_timer_emulate(vcpu); + kvm_timer_unblocking(vcpu); + /* If the timer fired while we weren't running, inject it now */ if (kvm_timer_should_fire(ptimer) != ptimer->irq.level) kvm_timer_update_irq(vcpu, !ptimer->irq.level, ptimer); @@ -527,6 +517,9 @@ void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu) */ soft_timer_cancel(&timer->phys_timer); + if (swait_active(kvm_arch_vcpu_wq(vcpu))) + kvm_timer_blocking(vcpu); + /* * The kernel may decide to run userspace after calling vcpu_put, so * we reset cntvoff to 0 to ensure a consistent read between user diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c index b77db673bb03..9fbdb9e1c51f 100644 --- a/virt/kvm/arm/arm.c +++ b/virt/kvm/arm/arm.c @@ -335,13 +335,11 @@ int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu) void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) { - kvm_timer_schedule(vcpu); kvm_vgic_v4_enable_doorbell(vcpu); } void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) { - kvm_timer_unschedule(vcpu); kvm_vgic_v4_disable_doorbell(vcpu); } -- 2.18.0 _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm