| From c09d65d9eab69985c75f98ed64541229f6fa9aa6 Mon Sep 17 00:00:00 2001 |
| From: Liran Alon <liran.alon@oracle.com> |
| Date: Tue, 16 Apr 2019 20:36:34 +0300 |
| Subject: KVM: x86: Consider LAPIC TSC-Deadline timer expired if deadline too short |
| |
| 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, |
