From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH 2/4] KVM: x86: refactor PIT state inject_lock Date: Wed, 3 Feb 2016 17:45:09 +0100 Message-ID: <56B22E95.30504@redhat.com> References: <1454516585-28491-1-git-send-email-rkrcmar@redhat.com> <1454516585-28491-3-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, Yuki Shibuya To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , linux-kernel@vger.kernel.org Return-path: In-Reply-To: <1454516585-28491-3-git-send-email-rkrcmar@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 03/02/2016 17:23, Radim Kr=C4=8Dm=C3=A1=C5=99 wrote: > Following patches would be even uglier if inject_lock didn't go away. >=20 > Patch changes the virtual wire comment to better describe our situati= on. >=20 > Signed-off-by: Radim Kr=C4=8Dm=C3=A1=C5=99 > --- > arch/x86/kvm/i8254.c | 67 ++++++++++++++++++++++--------------------= ---------- > arch/x86/kvm/i8254.h | 3 +-- > 2 files changed, 29 insertions(+), 41 deletions(-) >=20 > diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c > index de5f5018026f..a137eb381012 100644 > --- a/arch/x86/kvm/i8254.c > +++ b/arch/x86/kvm/i8254.c > @@ -236,16 +236,13 @@ static void kvm_pit_ack_irq(struct kvm_irq_ack_= notifier *kian) > { > struct kvm_kpit_state *ps =3D container_of(kian, struct kvm_kpit_st= ate, > irq_ack_notifier); > - int value; > =20 > - spin_lock(&ps->inject_lock); > + atomic_set(&ps->irq_ack, 1); smp_mb__before_atomic(); > if (atomic_add_unless(&ps->pending, -1, 0)) > /* in this case, we had multiple outstanding pit interrupts > * that we needed to inject. Reinject > */ > queue_kthread_work(&ps->pit->worker, &ps->pit->expired); > - ps->irq_ack =3D 1; > - spin_unlock(&ps->inject_lock); > } > =20 > void __kvm_migrate_pit_timer(struct kvm_vcpu *vcpu) > @@ -276,34 +273,25 @@ static void pit_do_work(struct kthread_work *wo= rk) > struct kvm_vcpu *vcpu; > int i; > struct kvm_kpit_state *ps =3D &pit->pit_state; > - int inject =3D 0; > =20 > - /* Try to inject pending interrupts when > - * last one has been acked. > + if (!atomic_xchg(&ps->irq_ack, 0)) > + return; > + > + kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 1, false); > + kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 0, false); > + > + /* > + * Provides NMI watchdog support via Virtual Wire mode. > + * The route is: PIT -> LVT0 in NMI mode. > + * > + * Note: Our Virtual Wire implementation does not follow > + * the MP specification. We propagate a PIT interrupt to all > + * VCPUs and only when LVT0 is in NMI mode. The interrupt can > + * also be simultaneously delivered through PIC and IOAPIC. > */ > - spin_lock(&ps->inject_lock); > - if (ps->irq_ack) { > - ps->irq_ack =3D 0; > - inject =3D 1; > - } > - spin_unlock(&ps->inject_lock); > - if (inject) { > - kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 1, false); > - kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 0, false); > - > - /* > - * Provides NMI watchdog support via Virtual Wire mode. > - * The route is: PIT -> PIC -> LVT0 in NMI mode. > - * > - * Note: Our Virtual Wire implementation is simplified, only > - * propagating PIT interrupts to all VCPUs when they have set > - * LVT0 to NMI delivery. Other PIC interrupts are just sent to > - * VCPU0, and only if its LVT0 is in EXTINT mode. > - */ > - if (atomic_read(&kvm->arch.vapics_in_nmi_mode) > 0) > - kvm_for_each_vcpu(i, vcpu, kvm) > - kvm_apic_nmi_wd_deliver(vcpu); > - } > + if (atomic_read(&kvm->arch.vapics_in_nmi_mode) > 0) > + kvm_for_each_vcpu(i, vcpu, kvm) > + kvm_apic_nmi_wd_deliver(vcpu); > } > =20 > static enum hrtimer_restart pit_timer_fn(struct hrtimer *data) > @@ -323,6 +311,12 @@ static enum hrtimer_restart pit_timer_fn(struct = hrtimer *data) > return HRTIMER_NORESTART; > } > =20 > +static void kvm_pit_reset_reinject(struct kvm_pit *pit) > +{ > + atomic_set(&pit->pit_state.pending, 0); smp_wmb()? Looks safe otherwise. (Please also add a comment before the memory barriers to show the pairing). Paolo