linux-kernel - [PATCH 0/4] KVM: x86: change and fix PIT discard tick policy

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Date:	Wed,  3 Feb 2016 17:23:01 +0100
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
	Yuki Shibuya <shibuya.yk@...s.nec.co.jp>
Subject: [PATCH 0/4] KVM: x86: change and fix PIT discard tick policy

[3/4] fixes a bug where legacy NMI watchdog doesn't receive NMIs if a
CPU that handles PIT interrupts hangs with masked interrupts.

Remaining patches try to make the code nicer where necessary.
([1/4] makes you think that it fixes a bug, but that would be fixed by
 skipping the path in [3/4].)

[3/4] only changes the discard policy.  A change that allows legacy NMI
watchdog with the reinject policy is below, but conscience doesn't allow
me to sign it off.

# diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
@@ -274,6 +274,10 @@ static void pit_do_work(struct kthread_work *work)
 	int i;
 	struct kvm_kpit_state *ps = &pit->pit_state;
 
+	if (atomic_read(&kvm->arch.vapics_in_nmi_mode) > 0)
+		kvm_for_each_vcpu(i, vcpu, kvm)
+			kvm_apic_nmi_wd_deliver(vcpu);
+
 	if (ps->reinject && !atomic_xchg(&ps->irq_ack, 0))
 		return;
 
@@ -289,9 +293,6 @@ static void pit_do_work(struct kthread_work *work)
	 * VCPUs and only when LVT0 is in NMI mode.  The interrupt can
	 * also be simultaneously delivered through PIC and IOAPIC.
 	 */
-	if (atomic_read(&kvm->arch.vapics_in_nmi_mode) > 0)
-		kvm_for_each_vcpu(i, vcpu, kvm)
-			kvm_apic_nmi_wd_deliver(vcpu);
 }
 
 static enum hrtimer_restart pit_timer_fn(struct hrtimer *data)


Radim Krčmář (4):
  KVM: x86: fix interrupt dropping race in PIT
  KVM: x86: refactor PIT state inject_lock
  KVM: x86: change PIT discard tick policy
  KVM: x86: remove notifiers from PIT discard policy

 arch/x86/kvm/i8254.c | 122 ++++++++++++++++++++++++++-------------------------
 arch/x86/kvm/i8254.h |   4 +-
 arch/x86/kvm/x86.c   |   6 +--
 3 files changed, 67 insertions(+), 65 deletions(-)

-- 
2.7.0