From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCH] remove static declaration from wall clock version Date: Fri, 27 Feb 2009 13:44:05 -0300 Message-ID: <20090227164405.GA10181@amt.cnet> References: <1235677340-3139-1-git-send-email-glommer@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm@vger.kernel.org, avi@redhat.com To: Glauber Costa Return-path: Received: from mx2.redhat.com ([66.187.237.31]:59457 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758534AbZB0Qor (ORCPT ); Fri, 27 Feb 2009 11:44:47 -0500 Received: from int-mx2.corp.redhat.com (int-mx2.corp.redhat.com [172.16.27.26]) by mx2.redhat.com (8.13.8/8.13.8) with ESMTP id n1RGijbF001185 for ; Fri, 27 Feb 2009 11:44:45 -0500 Content-Disposition: inline In-Reply-To: <1235677340-3139-1-git-send-email-glommer@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Matt T. Yourst noted that we're currently having a dumb race for no reason in paravirtual wall clock. This is due to the use of a static variable to hold the counting. This can race with multiple guests reading wallclock at the same time, since the static variable value would then be accessible to all callers. This wasn't noted before because it is a rather rare scenario. Instead, just use a normal stack variable. This will mean that each caller will have it's version written separatedly. No need for a global counter. Signed-off-by: Glauber Costa Acked-by: Marcelo Tosatti --- arch/x86/kvm/x86.c | 4 +--- 1 files changed, 1 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 2511708..d7236f6 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -548,15 +548,13 @@ static int do_set_msr(struct kvm_vcpu *vcpu, unsigned index, u64 *data) static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock) { - static int version; + int version = 1; struct pvclock_wall_clock wc; struct timespec now, sys, boot; if (!wall_clock) return; - version++; - kvm_write_guest(kvm, wall_clock, &version, sizeof(version)); /* -- 1.5.6.5