[PATCH 6.12 220/567] KVM: x86: WARN if hrtimer callback for periodic APIC timer fires with period=0

Greg Kroah-Hartman
2026-01-06T17:26:21Z

From: Sean Christopherson <seanjc@google.com>

commit 0ea9494be9c931ddbc084ad5e11fda91b554cf47 upstream.

WARN and don't restart the hrtimer if KVM's callback runs with the guest's
APIC timer in periodic mode but with a period of '0', as not advancing the
hrtimer's deadline would put the CPU into an infinite loop of hrtimer
events. Observing a period of '0' should be impossible, even when the
hrtimer is running on a different CPU than the vCPU, as KVM is supposed to
cancel the hrtimer before changing (or zeroing) the period, e.g. when
switching from periodic to one-shot.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20251113205114.1647493-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kvm/lapic.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2869,7 +2869,7 @@ static enum hrtimer_restart apic_timer_f

apic_timer_expired(apic, true);

- if (lapic_is_periodic(apic)) {
+ if (lapic_is_periodic(apic) && !WARN_ON_ONCE(!apic->lapic_timer.period)) {
advance_periodic_target_expiration(apic);
hrtimer_add_expires_ns(&ktimer->timer, ktimer->period);
return HRTIMER_RESTART;