From 7afc4ddbf299a13aaf28406783d141a34c6b4f5a Mon Sep 17 00:00:00 2001 From: Christoffer Dall Date: Wed, 25 Jul 2018 10:21:27 +0100 Subject: KVM: arm/arm64: Fix potential loss of ptimer interrupts kvm_timer_update_state() is called when changing the phys timer configuration registers, either via vcpu reset, as a result of a trap from the guest, or when userspace programs the registers. phys_timer_emulate() is in turn called by kvm_timer_update_state() to either cancel an existing software timer, or program a new software timer, to emulate the behavior of a real phys timer, based on the change in configuration registers. Unfortunately, the interaction between these two functions left a small race; if the conceptual emulated phys timer should actually fire, but the soft timer hasn't executed its callback yet, we cancel the timer in phys_timer_emulate without injecting an irq. This only happens if the check in kvm_timer_update_state is called before the timer should fire, which is relatively unlikely, but possible. The solution is to update the state of the phys timer after calling phys_timer_emulate, which will pick up the pending timer state and update the interrupt value. Note that this leaves the opportunity of raising the interrupt twice, once in the just-programmed soft timer, and once in kvm_timer_update_state. Since this always happens synchronously with the VCPU execution, there is no harm in this, and the guest ever only sees a single timer interrupt. Cc: Stable # 4.15+ Signed-off-by: Christoffer Dall Signed-off-by: Marc Zyngier --- virt/kvm/arm/arch_timer.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) (limited to 'virt/kvm/arm/arch_timer.c') diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c index bd3d57f40f1b..18ff6203079d 100644 --- a/virt/kvm/arm/arch_timer.c +++ b/virt/kvm/arm/arch_timer.c @@ -295,9 +295,9 @@ static void phys_timer_emulate(struct kvm_vcpu *vcpu) struct arch_timer_context *ptimer = vcpu_ptimer(vcpu); /* - * If the timer can fire now we have just raised the IRQ line and we - * don't need to have a soft timer scheduled for the future. If the - * timer cannot fire at all, then we also don't need a soft timer. + * If the timer can fire now, we don't need to have a soft timer + * scheduled for the future. If the timer cannot fire at all, + * then we also don't need a soft timer. */ if (kvm_timer_should_fire(ptimer) || !kvm_timer_irq_can_fire(ptimer)) { soft_timer_cancel(&timer->phys_timer, NULL); @@ -332,10 +332,10 @@ static void kvm_timer_update_state(struct kvm_vcpu *vcpu) level = kvm_timer_should_fire(vtimer); kvm_timer_update_irq(vcpu, level, vtimer); + phys_timer_emulate(vcpu); + if (kvm_timer_should_fire(ptimer) != ptimer->irq.level) kvm_timer_update_irq(vcpu, !ptimer->irq.level, ptimer); - - phys_timer_emulate(vcpu); } static void vtimer_save_state(struct kvm_vcpu *vcpu) -- cgit v1.2.3 From 245715cbe83ca934af5d20e078fd85175c62995e Mon Sep 17 00:00:00 2001 From: Christoffer Dall Date: Wed, 25 Jul 2018 10:21:28 +0100 Subject: KVM: arm/arm64: Fix lost IRQs from emulated physcial timer when blocked When the VCPU is blocked (for example from WFI) we don't inject the physical timer interrupt if it should fire while the CPU is blocked, but instead we just wake up the VCPU and expect kvm_timer_vcpu_load to take care of injecting the interrupt. Unfortunately, kvm_timer_vcpu_load() doesn't actually do that, it only has support to schedule a soft timer if the emulated phys timer is expected to fire in the future. Follow the same pattern as kvm_timer_update_state() and update the irq state after potentially scheduling a soft timer. Reported-by: Andre Przywara Cc: Stable # 4.15+ Fixes: bbdd52cfcba29 ("KVM: arm/arm64: Avoid phys timer emulation in vcpu entry/exit") Signed-off-by: Christoffer Dall Signed-off-by: Marc Zyngier --- virt/kvm/arm/arch_timer.c | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'virt/kvm/arm/arch_timer.c') diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c index 18ff6203079d..17cecc96f735 100644 --- a/virt/kvm/arm/arch_timer.c +++ b/virt/kvm/arm/arch_timer.c @@ -487,6 +487,7 @@ void kvm_timer_vcpu_load(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); if (unlikely(!timer->enabled)) return; @@ -502,6 +503,10 @@ void kvm_timer_vcpu_load(struct kvm_vcpu *vcpu) /* Set the background timer for the physical timer emulation. */ phys_timer_emulate(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); } bool kvm_timer_should_notify_user(struct kvm_vcpu *vcpu) -- cgit v1.2.3