KVM: x86: make vapics_in_nmi_mode atomic

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.)

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
[Actually the next patch makes it much, much easier to trigger the race
 so I'm including this one for stable@ as well. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 9171618..93ce7e4 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -472,7 +472,7 @@ 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;
 
        unsigned int tss_addr;
        struct page *apic_access_page;

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index cced57f..ab98fe5 100644 (file)
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -318,7 +318,7 @@ static void pit_do_work(struct work_struct *work)
                 * 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);
        }

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 176205a..a64672a 100644 (file)
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -757,10 +757,10 @@ static void apic_manage_nmi_watchdog(struct kvm_lapic *apic, u32 lvt0_val)
                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)