diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index a5c927e7bae6..8b6ec3304100 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -2131,15 +2131,33 @@ static void advance_periodic_target_expiration(struct kvm_lapic *apic) ktime_t delta; /* - * Synchronize both deadlines to the same time source or - * differences in the periods (caused by differences in the - * underlying clocks or numerical approximation errors) will - * cause the two to drift apart over time as the errors - * accumulate. + * Use kernel time as the time source for both the hrtimer deadline and + * TSC-based deadline so that they stay synchronized. Computing each + * deadline independently will cause the two deadlines to drift apart + * over time as differences in the periods accumulate, e.g. due to + * differences in the underlying clocks or numerical approximation errors. */ apic->lapic_timer.target_expiration = ktime_add_ns(apic->lapic_timer.target_expiration, apic->lapic_timer.period); + + /* + * If the new expiration is in the past, e.g. because userspace stopped + * running the VM for an extended duration, then force the expiration + * to "now" and don't try to play catch-up with the missed events. KVM + * will only deliver a single interrupt regardless of how many events + * are pending, i.e. restarting the timer with an expiration in the + * past will do nothing more than waste host cycles, and can even lead + * to a hard lockup in extreme cases. + */ + if (ktime_before(apic->lapic_timer.target_expiration, now)) + apic->lapic_timer.target_expiration = now; + + /* + * Note, ensuring the expiration isn't in the past also prevents delta + * from going negative, which could cause the TSC deadline to become + * excessively large due to it an unsigned value. + */ delta = ktime_sub(apic->lapic_timer.target_expiration, now); apic->lapic_timer.tscdeadline = kvm_read_l1_tsc(apic->vcpu, tscl) + nsec_to_cycles(apic->vcpu, delta);