From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH 3/3] KVM: x86: make vapics_in_nmi_mode atomic Date: Wed, 1 Jul 2015 15:33:41 +0200 Message-ID: <5593EC35.6060509@redhat.com> References: <1435695558-3168-1-git-send-email-rkrcmar@redhat.com> <1435695558-3168-4-git-send-email-rkrcmar@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: kvm@vger.kernel.org, Yoshida Nobuo To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , linux-kernel@vger.kernel.org Return-path: In-Reply-To: <1435695558-3168-4-git-send-email-rkrcmar@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 30/06/2015 22:19, Radim Kr=C4=8Dm=C3=A1=C5=99 wrote: > 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.) I suspect patch 2 makes this race much easier to trigger, so it deserve= s Cc: stable@ as well. Paolo > Signed-off-by: Radim Kr=C4=8Dm=C3=A1=C5=99 > --- > 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(-) >=20 > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/k= vm_host.h > index c7fa57b529d2..2a7f5d782c33 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -607,7 +607,7 @@ 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; > =20 > diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c > index 4dce6f8b6129..f90952f64e79 100644 > --- a/arch/x86/kvm/i8254.c > +++ b/arch/x86/kvm/i8254.c > @@ -305,7 +305,7 @@ static void pit_do_work(struct kthread_work *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 8dc32b5a4e0d..954e98a8c2e3 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -1264,9 +1264,9 @@ static void apic_manage_nmi_watchdog(struct kvm= _lapic *apic, u32 lvt0_val) > if (lvt0_in_nmi_mode) { > 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 > - apic->vcpu->kvm->arch.vapics_in_nmi_mode--; > + atomic_dec(&apic->vcpu->kvm->arch.vapics_in_nmi_mode); > } > } > =20 >=20