linux-kernel - [tip:timers/core] KVM: LAPIC: Mark hrtimer to expire in hard interrupt context

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Message-ID: <tip-899ad4bce00d10433b64647a37f6488dd8b582c9@git.kernel.org>
Date:   Tue, 30 Jul 2019 15:14:12 -0700
From:   tip-bot for Sebastian Andrzej Siewior <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, bigeasy@...utronix.de,
        pbonzini@...hat.com, tglx@...utronix.de, hpa@...or.com,
        mingo@...nel.org, peterz@...radead.org
Subject: [tip:timers/core] KVM: LAPIC: Mark hrtimer to expire in hard
 interrupt context

Commit-ID:  899ad4bce00d10433b64647a37f6488dd8b582c9
Gitweb:     https://git.kernel.org/tip/899ad4bce00d10433b64647a37f6488dd8b582c9
Author:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
AuthorDate: Fri, 26 Jul 2019 20:30:55 +0200
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Tue, 30 Jul 2019 23:57:55 +0200

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@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Paolo Bonzini <pbonzini@...hat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20190726185753.363363474@linutronix.de

---
 arch/x86/kvm/lapic.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 0aa158657f20..b9e516099d07 100644
--- 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);
 }
 
 /*