On 16/07/18 18:23, Andre Przywara wrote:
> When KVM emulates a physical timer, we keep track of the interrupt
> condition and try to inject an IRQ to the guest when needed.
> This works if the timer expires when either the guest is running or KVM
> does work on behalf of it, since it calls kvm_timer_update_state().
> However when the guest's VCPU is not scheduled (for instance because
> the guest issued a WFI instruction before), we miss injecting the interrupt
> when the VCPU's state gets restored back in kvm_timer_vcpu_load().
>
> Fix this by moving the interrupt injection check into the
> phys_timer_emulate() function, so that all possible paths of execution
> are covered.
>
> This fixes the physical timer emulation, which broke when it got changed
> in the 4.15 merge window.
> The respective kvm-unit-test check has been posted already.
>
> Cc: Stable <stable@xxxxxxxxxxxxxxx> # 4.15+
> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
> ---
> virt/kvm/arm/arch_timer.c | 21 +++++++++++++--------
> 1 file changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
> index bd3d57f40f1b..1949fb0b80a4 100644
> --- a/virt/kvm/arm/arch_timer.c
> +++ b/virt/kvm/arm/arch_timer.c
> @@ -294,17 +294,26 @@ static void phys_timer_emulate(struct kvm_vcpu *vcpu)
> struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> struct arch_timer_context *ptimer = vcpu_ptimer(vcpu);
>
> + /* If the timer cannot fire at all, then we don't need a soft timer. */
> + if (!kvm_timer_irq_can_fire(ptimer)) {
> + soft_timer_cancel(&timer->phys_timer, NULL);
> + kvm_timer_update_irq(vcpu, false, ptimer);
> + return;
> + }
> +
> /*
> - * 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, as we also raise the IRQ line.
> */
> - if (kvm_timer_should_fire(ptimer) || !kvm_timer_irq_can_fire(ptimer)) {
> + if (kvm_timer_should_fire(ptimer)) {
> soft_timer_cancel(&timer->phys_timer, NULL);
> + kvm_timer_update_irq(vcpu, true, ptimer);
> +
> return;
> }
>
> soft_timer_start(&timer->phys_timer, kvm_timer_compute_delta(ptimer));
> + kvm_timer_update_irq(vcpu, false, ptimer);
I think this bit is wrong. The soft timer could have expired by the time
you get to lower the line, and you would just loose that interrupt.
Lowering the line *before* starting the soft timer would make a lot more
sense to me.
> }
>
> /*
> @@ -316,7 +325,6 @@ static void kvm_timer_update_state(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);
> bool level;
>
> if (unlikely(!timer->enabled))
> @@ -332,9 +340,6 @@ static void kvm_timer_update_state(struct kvm_vcpu *vcpu)
> level = kvm_timer_should_fire(vtimer);
> kvm_timer_update_irq(vcpu, level, vtimer);
>
> - if (kvm_timer_should_fire(ptimer) != ptimer->irq.level)
> - kvm_timer_update_irq(vcpu, !ptimer->irq.level, ptimer);
> -
> phys_timer_emulate(vcpu);
> }
>
>
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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