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: Thu, 23 Apr 2015 08:51:17 -0300 Message-ID: <20150423115117.GA32371@amt.cnet> References: <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> <20150422212148.GA17494@amt.cnet> <5538B7B3.2020009@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andy Lutomirski , Peter Zijlstra , Linus Torvalds , "linux-kernel@vger.kernel.org" , Gleb Natapov , kvm list , Ralf Baechle , Andrew Lutomirski To: Paolo Bonzini Return-path: Content-Disposition: inline In-Reply-To: <5538B7B3.2020009@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Thu, Apr 23, 2015 at 11:13:23AM +0200, Paolo Bonzini wrote: > > > On 22/04/2015 23:21, Marcelo Tosatti wrote: > > On Mon, Apr 20, 2015 at 01:27:58PM -0700, Andy Lutomirski wrote: > >> On Mon, Apr 20, 2015 at 9:59 AM, 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? Was it supposed to work even 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? 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. > >> > >> I don't think anyone ever tried that hard to test this stuff. There > >> was an infinte loop that Firefox was triggering as a KVM guest > >> somewhat reliably until a couple months ago in the same vdso code. :( > > > > https://bugzilla.redhat.com/show_bug.cgi?id=1174664 > > That was the missing volatile in an asm. Older compilers didn't catch > it. :( How do you know that? It looks like memory corruption (look at the pattern at the end).