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

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 12/04/2013 12:16 PM, 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?
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

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