From mboxrd@z Thu Jan  1 00:00:00 1970
From: George Dunlap <george.dunlap@eu.citrix.com>
Subject: Re: XSA-60 - how to get back to a sane state
Date: Tue, 3 Dec 2013 15:14:57 +0000
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To: Jan Beulich <JBeulich@suse.com>, Andrew Cooper <andrew.cooper3@citrix.com>, Jinsong Liu <jinsong.liu@intel.com>, xen-devel <xen-devel@lists.xenproject.org>
Cc: Zhenzhong Duan <zhenzhong.duan@oracle.com>, Keir Fraser <keir@xen.org>, Jun Nakajima <jun.nakajima@intel.com>, Donald D Dugger <donald.d.dugger@intel.com>
List-Id: xen-devel@lists.xenproject.org

On 12/03/2013 03:09 PM, Jan Beulich wrote:
>>>> On 03.12.13 at 15:30, "Liu, Jinsong" <jinsong.liu@intel.com> wrote:
>> Jan Beulich wrote:
>>>>>> On 03.12.13 at 04:06, "Liu, Jinsong" <jinsong.liu@intel.com> 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.

Is this still about guests doing wbinvd?  As Jan said, there is no point 
in doing wbinvd piecemeal: if it's not 100% reliable (to the best of our 
knowledge), then the more unreliable the better really.

  -George