From: Liran Alon liran.alon@oracle.com
commit c09d65d9eab69985c75f98ed64541229f6fa9aa6 upstream.
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 joao.m.martins@oracle.com Signed-off-by: Liran Alon liran.alon@oracle.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kvm/lapic.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
--- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1543,9 +1543,12 @@ static void start_sw_tscdeadline(struct
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,