From c09d65d9eab69985c75f98ed64541229f6fa9aa6 Mon Sep 17 00:00:00 2001 From: Liran Alon Date: Tue, 16 Apr 2019 20:36:34 +0300 Subject: [PATCH] KVM: x86: Consider LAPIC TSC-Deadline timer expired if deadline too short If guest sets MSR_IA32_TSCDEADLINE to value such that in host time-domain it's shorter than lapic_timer_advance_ns, we can reach a case that we call hrtimer_start() with expiration time set at the past. Because lapic_timer.timer is init with HRTIMER_MODE_ABS_PINNED, it is not allowed to run in softirq and therefore will never expire. To avoid such a scenario, verify that deadline expiration time is set on host time-domain further than (now + lapic_timer_advance_ns). A future patch can also consider adding a min_timer_deadline_ns module parameter, similar to min_timer_period_us to avoid races that amount of ns it takes to run logic could still call hrtimer_start() with expiration timer set at the past. Reviewed-by: Joao Martins Signed-off-by: Liran Alon Signed-off-by: Paolo Bonzini --- arch/x86/kvm/lapic.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 9bf70cf84564..6cb990dbc15a 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1542,9 +1542,12 @@ static void start_sw_tscdeadline(struct kvm_lapic *apic) now = ktime_get(); guest_tsc = kvm_read_l1_tsc(vcpu, rdtsc()); - if (likely(tscdeadline > guest_tsc)) { - ns = (tscdeadline - guest_tsc) * 1000000ULL; - do_div(ns, this_tsc_khz); + + ns = (tscdeadline - guest_tsc) * 1000000ULL; + do_div(ns, this_tsc_khz); + + if (likely(tscdeadline > guest_tsc) && + likely(ns > lapic_timer_advance_ns)) { expire = ktime_add_ns(now, ns); expire = ktime_sub_ns(expire, lapic_timer_advance_ns); hrtimer_start(&apic->lapic_timer.timer,