Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754712AbcDZXVx (ORCPT ); Tue, 26 Apr 2016 19:21:53 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:40774 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754691AbcDZXVq (ORCPT ); Tue, 26 Apr 2016 19:21:46 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Paolo Bonzini" , "=?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?=" , "Yuki Shibuya" Date: Wed, 27 Apr 2016 01:02:21 +0200 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 065/217] KVM: i8254: change PIT discard tick policy In-Reply-To: X-SA-Exim-Connect-IP: 2a02:8426:ae4:c500:9cba:69ae:962d:6167 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2474 Lines: 72 3.16.35-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Radim Krčmář commit 7dd0fdff145c5be7146d0ac06732ae3613412ac1 upstream. Discard policy uses ack_notifiers to prevent injection of PIT interrupts before EOI from the last one. This patch changes the policy to always try to deliver the interrupt, which makes a difference when its vector is in ISR. Old implementation would drop the interrupt, but proposed one injects to IRR, like real hardware would. The old policy breaks legacy NMI watchdogs, where PIT is used through virtual wire (LVT0): PIT never sends an interrupt before receiving EOI, thus a guest deadlock with disabled interrupts will stop NMIs. Note that NMI doesn't do EOI, so PIT also had to send a normal interrupt through IOAPIC. (KVM's PIT is deeply rotten and luckily not used much in modern systems.) Even though there is a chance of regressions, I think we can fix the LVT0 NMI bug without introducing a new tick policy. Reported-by: Yuki Shibuya Reviewed-by: Paolo Bonzini Signed-off-by: Radim Krčmář Signed-off-by: Paolo Bonzini Signed-off-by: Ben Hutchings --- arch/x86/kvm/i8254.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) --- a/arch/x86/kvm/i8254.c +++ b/arch/x86/kvm/i8254.c @@ -244,7 +244,7 @@ static void kvm_pit_ack_irq(struct kvm_i * PIC is being reset. Handle it gracefully here */ atomic_inc(&ps->pending); - else if (value > 0) + else if (value > 0 && ps->reinject) /* in this case, we had multiple outstanding pit interrupts * that we needed to inject. Reinject */ @@ -287,7 +287,9 @@ static void pit_do_work(struct kthread_w * last one has been acked. */ spin_lock(&ps->inject_lock); - if (ps->irq_ack) { + if (!ps->reinject) + inject = 1; + else if (ps->irq_ack) { ps->irq_ack = 0; inject = 1; } @@ -316,10 +318,10 @@ static enum hrtimer_restart pit_timer_fn struct kvm_kpit_state *ps = container_of(data, struct kvm_kpit_state, timer); struct kvm_pit *pt = ps->kvm->arch.vpit; - if (ps->reinject || !atomic_read(&ps->pending)) { + if (ps->reinject) atomic_inc(&ps->pending); - queue_kthread_work(&pt->worker, &pt->expired); - } + + queue_kthread_work(&pt->worker, &pt->expired); if (ps->is_periodic) { hrtimer_add_expires_ns(&ps->timer, ps->period);