Re: [Xen-devel] XSA-60 - how to get back to a sane state

["Liu, Jinsong" <jinsong.liu@xxxxxxxxx>]

Jan Beulich wrote:
>>>> On 04.12.13 at 13:04, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx> wrote:
>> Jan Beulich wrote:
>>>>>> On 03.12.13 at 15:30, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx>
>>>>>> wrote: 
>>>> Jan Beulich wrote:
>>>>>>>> On 03.12.13 at 04:06, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx>
>>>>>>>> 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?
> 

Before my 4 patches (in fact before the 3rd patch 62652c00), Xen just didn't 
take care of the case.
Notice that wbinvd at vmx_ctxt_switch_to is for a corner case (when uc mode).

Thanks,
Jinsong
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