From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [GIT PULL] First batch of KVM changes for 4.1 Date: Wed, 22 Apr 2015 17:56:02 -0300 Message-ID: <20150422205602.GA15317@amt.cnet> References: <20150417103654.GE5029@twins.programming.kicks-ass.net> <5530E28F.2030401@redhat.com> <20150417105506.GF5029@twins.programming.kicks-ass.net> <553100C1.5000408@redhat.com> <20150417131037.GG23123@twins.programming.kicks-ass.net> <55310CF2.6070107@redhat.com> <20150417190146.GA24395@amt.cnet> <55316598.908@redhat.com> <20150417201841.GA31302@amt.cnet> <55353058.2000008@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Peter Zijlstra , torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, gleb@kernel.org, kvm@vger.kernel.org, Ralf Baechle , luto@kernel.org To: Paolo Bonzini Return-path: Content-Disposition: inline In-Reply-To: <55353058.2000008@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Mon, Apr 20, 2015 at 06:59:04PM +0200, Paolo Bonzini wrote: > > > On 17/04/2015 22:18, Marcelo Tosatti wrote: > > The bug which this is fixing is very rare, have no memory of a report. > > > > In fact, its even difficult to create a synthetic reproducer. > > But then why was the task migration notifier even in Jeremy's original > code for Xen? To cover for the vcpu1 -> vcpu2 -> vcpu1 case, i believe. > Was it supposed to work even on non-synchronized TSC? Yes it is supposed to work on non-synchronized TSC. > If that's the case, then it could be reverted indeed; but then why did > you commit this patch to 4.1? Because it fixes the problem Andy reported (see Subject: KVM: x86: fix kvmclock write race (v2) on kvm@). As long as you have Radim's fix on top. > Did you think of something that would > cause the seqcount-like protocol to fail, and that turned out not to be > the case later? I was only following the mailing list sparsely in March. No.