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

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 12/03/2013 03:09 PM, 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.
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

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