Patch "KVM: x86: make vapics_in_nmi_mode atomic" has been added to the 4.0-stable tree

This is a note to let you know that I've just added the patch titled

KVM: x86: make vapics_in_nmi_mode atomic

to the 4.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kvm-x86-make-vapics_in_nmi_mode-atomic.patch
and it can be found in the queue-4.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= <[email protected]>
Date: Wed, 1 Jul 2015 15:31:49 +0200
Subject: KVM: x86: make vapics_in_nmi_mode atomic
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From: =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= <[email protected]>

commit 42720138b06301cc8a7ee8a495a6d021c4b6a9bc upstream.

Writes were a bit racy, but hard to turn into a bug at the same time. (Particularly because modern Linux doesn't use this feature anymore.)

[Actually the next patch makes it much, much easier to trigger the race
so I'm including this one for stable@ as well. - Paolo]

---
 arch/x86/include/asm/kvm_host.h |    2 +-
 arch/x86/kvm/i8254.c            |    2 +-
 arch/x86/kvm/lapic.c            |    4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

@@ -583,7 +583,7 @@ struct kvm_arch {
 	struct kvm_pic *vpic;
 	struct kvm_ioapic *vioapic;
 	struct kvm_pit *vpit;
-	int vapics_in_nmi_mode;
+	atomic_t vapics_in_nmi_mode;
 	struct mutex apic_map_lock;
 	struct kvm_apic_map *apic_map;
 

@@ -305,7 +305,7 @@ static void pit_do_work(struct kthread_w
 		 * LVT0 to NMI delivery. Other PIC interrupts are just sent to
 		 * VCPU0, and only if its LVT0 is in EXTINT mode.
 		 */
-		if (kvm->arch.vapics_in_nmi_mode > 0)
+		if (atomic_read(&kvm->arch.vapics_in_nmi_mode) > 0)
 			kvm_for_each_vcpu(i, vcpu, kvm)
 				kvm_apic_nmi_wd_deliver(vcpu);
 	}

@@ -1224,10 +1224,10 @@ static void apic_manage_nmi_watchdog(str
 		if (!nmi_wd_enabled) {
 			apic_debug("Receive NMI setting on APIC_LVT0 "
 				   "for cpu %d\n", apic->vcpu->vcpu_id);
-			apic->vcpu->kvm->arch.vapics_in_nmi_mode++;
+			atomic_inc(&apic->vcpu->kvm->arch.vapics_in_nmi_mode);
 		}
 	} else if (nmi_wd_enabled)
-		apic->vcpu->kvm->arch.vapics_in_nmi_mode--;
+		atomic_dec(&apic->vcpu->kvm->arch.vapics_in_nmi_mode);
 }
 
 static int apic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)

Patches currently in stable-queue which might be from [email protected] are

queue-4.0/kvm-x86-properly-restore-lvt0.patch queue-4.0/kvm-x86-make-vapics_in_nmi_mode-atomic.patch