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| author | Christoffer Dall <christoffer.dall@arm.com> | 2018-07-25 12:21:27 +0300 |
|---|---|---|
| committer | Marc Zyngier <marc.zyngier@arm.com> | 2018-07-31 09:53:16 +0300 |
| commit | 7afc4ddbf299a13aaf28406783d141a34c6b4f5a (patch) | |
| tree | cec0e2433b589023c205041a63111b8ecc71309a /virt/kvm | |
| parent | 6b8b9a48545e08345b8ff77c9fd51b1aebdbefb3 (diff) | |
| download | linux-7afc4ddbf299a13aaf28406783d141a34c6b4f5a.tar.xz | |
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/kvm')
| -rw-r--r-- | virt/kvm/arm/arch_timer.c | 10 |
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) |