Il 08/10/2014 12:06, Radim Krčmář ha scritto:
> KVM: x86: fix deadline tsc interrupt injection
>
> The check in kvm_set_lapic_tscdeadline_msr() was trying to prevent a
> situation where we lose a pending deadline timer in a MSR write.
> Losing it is fine, because it effectively occurs before the timer fired,
> so we should be able to cancel or postpone it.
>
> Another problem comes from interaction with QEMU, or other userspace
> that can set deadline MSR without a good reason, when timer is already
> pending: one guest's deadline request results in more than one
> interrupt because one is injected immediately on MSR write from
> userspace and one through hrtimer later.
>
> The solution is to remove the injection when replacing a pending timer
> and to improve the usual QEMU path, we inject without a hrtimer when the
> deadline has already passed.
>
> Signed-off-by: Radim Krčmář <[email protected]>
> Reported-by: Nadav Amit <[email protected]>
> ---
> arch/x86/kvm/lapic.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index b8345dd..51428dd 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1096,9 +1096,12 @@ static void start_apic_timer(struct kvm_lapic *apic)
> if (likely(tscdeadline > guest_tsc)) {
> ns = (tscdeadline - guest_tsc) * 1000000ULL;
> do_div(ns, this_tsc_khz);
> + hrtimer_start(&apic->lapic_timer.timer,
> + ktime_add_ns(now, ns), HRTIMER_MODE_ABS);
> + } else {
> + atomic_inc(&ktimer->pending);
> + kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu);
> }
> - hrtimer_start(&apic->lapic_timer.timer,
> - ktime_add_ns(now, ns), HRTIMER_MODE_ABS);
>
> local_irq_restore(flags);
> }
> @@ -1355,9 +1358,6 @@ void kvm_set_lapic_tscdeadline_msr(struct kvm_vcpu
> *vcpu, u64 data)
> return;
>
> hrtimer_cancel(&apic->lapic_timer.timer);
> - /* Inject here so clearing tscdeadline won't override new value */
> - if (apic_has_pending_timer(vcpu))
> - kvm_inject_apic_timer_irqs(vcpu);
> apic->lapic_timer.tscdeadline = data;
> start_apic_timer(apic);
> }
Radim, the patch looks good but please extract this code:
/*
* There is a race window between reading and incrementing, but we do
* not care about potentially losing timer events in the !reinject
* case anyway. Note: KVM_REQ_PENDING_TIMER is implicitly checked
* in vcpu_enter_guest.
*/
if (!atomic_read(&ktimer->pending)) {
atomic_inc(&ktimer->pending);
/* FIXME: this code should not know anything about vcpus */
kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu);
}
if (waitqueue_active(q))
wake_up_interruptible(q);
to a new "static void apic_timer_expired(struct kvm_lapic *apic)" function,
and call it from both apic_timer_fn and start_apic_timer.
Also, we should not need to do wake_up_interruptible() unless we have
changed ktimer->pending from zero to non-zero.
Paolo
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