From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758144AbbDVVCY (ORCPT ); Wed, 22 Apr 2015 17:02:24 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39939 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753383AbbDVVCW (ORCPT ); Wed, 22 Apr 2015 17:02:22 -0400 Message-ID: <55380C3D.2080906@redhat.com> Date: Wed, 22 Apr 2015 23:01:49 +0200 From: Paolo Bonzini User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 MIME-Version: 1.0 To: Marcelo Tosatti CC: Peter Zijlstra , torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, gleb@kernel.org, kvm@vger.kernel.org, Ralf Baechle , luto@kernel.org Subject: Re: [GIT PULL] First batch of KVM changes for 4.1 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> <20150422205602.GA15317@amt.cnet> In-Reply-To: <20150422205602.GA15317@amt.cnet> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 22/04/2015 22:56, Marcelo Tosatti wrote: >> > 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. Ok, to cover it for non-synchronized TSC. While KVM requires 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. But if it's so rare, and it was known that fixing the host protocol was just as good a solution, why was the guest fix committed? I'm just trying to understand. I am worried that this patch was rushed in; so far I had assumed it wasn't (a revert of a revert is rare enough that you don't do it lightly...) but maybe I was wrong. Right now I cannot even decide whether to revert it (and please Peter in the process :)) or submit the Kconfig symbol patch officially. Paolo