From mboxrd@z Thu Jan 1 00:00:00 1970 From: George Dunlap Subject: Re: XSA-60 - how to get back to a sane state Date: Wed, 4 Dec 2013 15:55:43 +0000 Message-ID: <529F507F.2030304@eu.citrix.com> References: <529CA7250200007800108CB8@nat28.tlf.novell.com> <529CE2D5.7030805@eu.citrix.com> <529D4030.6040501@citrix.com> <529D9DA902000078001092BC@nat28.tlf.novell.com> <529E022D02000078001097C8@nat28.tlf.novell.com> <529F2B260200007800109FF3@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta3.messagelabs.com ([195.245.230.39]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1VoEnq-0007I6-Mr for xen-devel@lists.xenproject.org; Wed, 04 Dec 2013 15:55:54 +0000 In-Reply-To: <529F2B260200007800109FF3@nat28.tlf.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich , Jinsong Liu Cc: Keir Fraser , Andrew Cooper , Zhenzhong Duan , Donald D Dugger , Jun Nakajima , xen-devel List-Id: xen-devel@lists.xenproject.org On 12/04/2013 12:16 PM, Jan Beulich wrote: >>>> On 04.12.13 at 13:04, "Liu, Jinsong" wrote: >> Jan Beulich wrote: >>>>>> On 03.12.13 at 15:30, "Liu, Jinsong" wrote: >>>> Jan Beulich wrote: >>>>>>>> On 03.12.13 at 04:06, "Liu, Jinsong" >>>>>>>> wrote: >>>>>> I also vote option 2, but only revert 86d60e85, keeping 62652c00 >>>>>> (wbinvd at vmx_ctxt_switch_to) since it's used to avoid being >>>>>> polluted when vcpu migrate to another cpu. >>>>> Please explain this in more detail. Both Andrew and I are concerned >>>>> about this extra, but pretty pointless (without being done so too in >>>>> other cases) wbinvd(). In particular you'd have to explain what its >>>>> counterpart was in the code prior to your four patch XSA-60 series. >>>> The wbinvd at vmx_ctxt_switch_to is for case like >>>> 1. vcpu runs at cpu A, flushing cache at vmx_handle_cd; >>>> 2. then the vcpu may switch out and migrate to cpu B; >>>> 3. historically cpu B may has cacheline polluted; >>>> so when the vcpu is scheduled to cpu B, we need flush cache. >>> But you didn't clarify whether/how this case was taken care of >>> _before_ your XSA-60 patches. >>> >> I didn't understand your question. What do you mean by 'before my XSA-60 >> patches'? > Before your 4 patch series was applied (e.g. consider plain > 4.3.1) - how was the situation taken care of that your change > to vmx_ctxt_switch_to() is intended to deal with? It sounds like Jan is saying: We would only consider a patch that would fix regressions in functionality caused by the 4-patch XSA-60 series. Was there the possibility for cacheline pollution in the scenario you describe above before XSA-60 was fixed? If not, then this is a regression and we might consider a patch to restore that functionality. If there was the possibility of the above scenario before the XSA-60 series, then it's not a regression; and therefore probably not something we want to accept at this point. Do I understand you properly, Jan? -George