From patchwork Wed Feb 3 16:23:04 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?b?UmFkaW0gS3LEjW3DocWZ?= X-Patchwork-Id: 8204881 Return-Path: X-Original-To: patchwork-kvm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork2.web.kernel.org (Postfix) with ESMTP id 2B33FBEEE5 for ; Wed, 3 Feb 2016 16:24:26 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 52F0A2025B for ; Wed, 3 Feb 2016 16:24:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6556920279 for ; Wed, 3 Feb 2016 16:24:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757796AbcBCQYQ (ORCPT ); Wed, 3 Feb 2016 11:24:16 -0500 Received: from mx1.redhat.com ([209.132.183.28]:57665 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757696AbcBCQYP (ORCPT ); Wed, 3 Feb 2016 11:24:15 -0500 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) by mx1.redhat.com (Postfix) with ESMTPS id ED431804F9; Wed, 3 Feb 2016 16:24:14 +0000 (UTC) Received: from potion ([10.34.1.163]) by int-mx14.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with SMTP id u13GOBEC027168; Wed, 3 Feb 2016 11:24:12 -0500 Received: by potion (sSMTP sendmail emulation); Wed, 03 Feb 2016 17:24:11 +0100 From: =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= To: linux-kernel@vger.kernel.org Cc: kvm@vger.kernel.org, Paolo Bonzini , Yuki Shibuya Subject: [PATCH 3/4] KVM: x86: change PIT discard tick policy Date: Wed, 3 Feb 2016 17:23:04 +0100 Message-Id: <1454516585-28491-4-git-send-email-rkrcmar@redhat.com> In-Reply-To: <1454516585-28491-1-git-send-email-rkrcmar@redhat.com> References: <1454516585-28491-1-git-send-email-rkrcmar@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.68 on 10.5.11.27 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Spam-Status: No, score=-6.3 required=5.0 tests=BAYES_00,HK_RANDOM_FROM, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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 Signed-off-by: Radim Kr?má? --- arch/x86/kvm/i8254.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c index a137eb381012..fc554fbf71a7 100644 --- a/arch/x86/kvm/i8254.c +++ b/arch/x86/kvm/i8254.c @@ -237,6 +237,9 @@ static void kvm_pit_ack_irq(struct kvm_irq_ack_notifier *kian) struct kvm_kpit_state *ps = container_of(kian, struct kvm_kpit_state, irq_ack_notifier); + if (!ps->reinject) + return; + atomic_set(&ps->irq_ack, 1); if (atomic_add_unless(&ps->pending, -1, 0)) /* in this case, we had multiple outstanding pit interrupts @@ -274,7 +277,7 @@ static void pit_do_work(struct kthread_work *work) int i; struct kvm_kpit_state *ps = &pit->pit_state; - if (!atomic_xchg(&ps->irq_ack, 0)) + if (ps->reinject && !atomic_xchg(&ps->irq_ack, 0)) return; kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 1, false); @@ -299,10 +302,10 @@ static enum hrtimer_restart pit_timer_fn(struct hrtimer *data) 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);