path: root/virt
diff options
authorChristoffer Dall <christoffer.dall@arm.com>2018-07-25 10:21:27 +0100
committerMarc Zyngier <marc.zyngier@arm.com>2018-07-31 07:53:16 +0100
commit7afc4ddbf299a13aaf28406783d141a34c6b4f5a (patch)
treecec0e2433b589023c205041a63111b8ecc71309a /virt
parent6b8b9a48545e08345b8ff77c9fd51b1aebdbefb3 (diff)
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 <stable@vger.kernel.org> # 4.15+ Signed-off-by: Christoffer Dall <christoffer.dall@arm.com> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Diffstat (limited to 'virt')
1 files changed, 5 insertions, 5 deletions
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)