From patchwork Tue Jun 9 09:28:27 2009 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jan Kiszka X-Patchwork-Id: 28896 Received: from vger.kernel.org (vger.kernel.org [209.132.176.167]) by demeter.kernel.org (8.14.2/8.14.2) with ESMTP id n599Smqd017313 for ; Tue, 9 Jun 2009 09:28:48 GMT Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757909AbZFIJ2n (ORCPT ); Tue, 9 Jun 2009 05:28:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758288AbZFIJ2n (ORCPT ); Tue, 9 Jun 2009 05:28:43 -0400 Received: from gecko.sbs.de ([194.138.37.40]:16244 "EHLO gecko.sbs.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757145AbZFIJ2n (ORCPT ); Tue, 9 Jun 2009 05:28:43 -0400 Received: from mail2.sbs.de (localhost [127.0.0.1]) by gecko.sbs.de (8.12.11.20060308/8.12.11) with ESMTP id n599SRDU023964; Tue, 9 Jun 2009 11:28:27 +0200 Received: from [139.25.109.167] (mchn012c.mchp.siemens.de [139.25.109.167] (may be forged)) by mail2.sbs.de (8.12.11.20060308/8.12.11) with ESMTP id n599SREh008006; Tue, 9 Jun 2009 11:28:27 +0200 Message-ID: <4A2E2B3B.5020408@siemens.com> Date: Tue, 09 Jun 2009 11:28:27 +0200 From: Jan Kiszka User-Agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 MIME-Version: 1.0 To: Avi Kivity , kvm-devel CC: Marcelo Tosatti Subject: [PATCH] kvm: x86: Fix racy event propagation in kmv timer Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Minor issues that likely had no practical relevance: The kvm timer function so far incremented the pending counter and then may reset it again to 1 in case reinjection was disabled. This opened a small racy window with the corresponding VCPU loop that may have happened to run on another (real) CPU and already consumed the value. Moveover, the previous code tried to optimize the setting of KVM_REQ_PENDING_TIMER, but used atomic_inc_and_test - which always returns true unless pending had the invalid value of -1 on entry. Signed-off-by: Jan Kiszka --- arch/x86/kvm/timer.c | 11 +++++------ 1 files changed, 5 insertions(+), 6 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/arch/x86/kvm/timer.c b/arch/x86/kvm/timer.c index 86dbac0..18fd17c 100644 --- a/arch/x86/kvm/timer.c +++ b/arch/x86/kvm/timer.c @@ -9,12 +9,11 @@ static int __kvm_timer_fn(struct kvm_vcpu *vcpu, struct kvm_timer *ktimer) int restart_timer = 0; wait_queue_head_t *q = &vcpu->wq; - /* FIXME: this code should not know anything about vcpus */ - if (!atomic_inc_and_test(&ktimer->pending)) - set_bit(KVM_REQ_PENDING_TIMER, &vcpu->requests); - - if (!ktimer->reinject) - atomic_set(&ktimer->pending, 1); + if (ktimer->reinject || !atomic_read(&ktimer->pending)) { + /* FIXME: this code should not know anything about vcpus */ + if (atomic_inc_return(&ktimer->pending) == 1) + set_bit(KVM_REQ_PENDING_TIMER, &vcpu->requests); + } if (waitqueue_active(q)) wake_up_interruptible(q);