KVM: LAPIC: Mark hrtimer to expire in hard interrupt context

On PREEMPT_RT enabled kernels unmarked hrtimers are moved into soft
interrupt expiry mode by default.

While that's not a functional requirement for the KVM local APIC timer
emulation, it's a latency issue which can be avoided by marking the timer
so hard interrupt context expiry is enforced.

No functional change.

[ tglx: Split out from larger combo patch. Add changelog. ]

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20190726185753.363363474@linutronix.de

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 0aa158657f20cff83270f4251d1294030076c1bb..b9e516099d07e30ec64622902625fbd6d40cedd9 100644 (file)
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1601,7 +1601,7 @@ static void start_sw_tscdeadline(struct kvm_lapic *apic)
            likely(ns > apic->lapic_timer.timer_advance_ns)) {
                expire = ktime_add_ns(now, ns);
                expire = ktime_sub_ns(expire, ktimer->timer_advance_ns);
-               hrtimer_start(&ktimer->timer, expire, HRTIMER_MODE_ABS);
+               hrtimer_start(&ktimer->timer, expire, HRTIMER_MODE_ABS_HARD);
        } else
                apic_timer_expired(apic);
 
@@ -2302,7 +2302,7 @@ int kvm_create_lapic(struct kvm_vcpu *vcpu, int timer_advance_ns)
        apic->vcpu = vcpu;
 
        hrtimer_init(&apic->lapic_timer.timer, CLOCK_MONOTONIC,
-                    HRTIMER_MODE_ABS);
+                    HRTIMER_MODE_ABS_HARD);
        apic->lapic_timer.timer.function = apic_timer_fn;
        if (timer_advance_ns == -1) {
                apic->lapic_timer.timer_advance_ns = LAPIC_TIMER_ADVANCE_ADJUST_INIT;
@@ -2487,7 +2487,7 @@ void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
 
        timer = &vcpu->arch.apic->lapic_timer.timer;
        if (hrtimer_cancel(timer))
-               hrtimer_start_expires(timer, HRTIMER_MODE_ABS);
+               hrtimer_start_expires(timer, HRTIMER_MODE_ABS_HARD);
 }
 
 /*