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Re: [Xen-devel] Question about VPID during MOV-TO-CR3
On Sep 22, 2016 02:56, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
>
> >>> On 21.09.16 at 17:30, <tamas.lengyel@xxxxxxxxxxxx> wrote:
> > What I'm saying is that the guest OS should be in charge of managing
> > its own TLB when VPID is in use. Whether it does flush the TLB or not
> > is not of our concern. If it's a sane OS it will likely flush when it
> > needs to, but we should not be jumping in and doing it as we do right
> > now. We are actually breaking the architectural behavior by forcing a
> > flush, MOV-TO-CR3 doesn't by itself flush the TLB on real hardware.
>
> I continue to not understand where you take this from. Writes to
> CR3 have always been doing TLB flushes - full ones prior to the
> introduction of global pages, and flushes of only non-global entries
> nowadays. In fact prior to the introduction of INVLPG and CR4
> there was no other way to flush TLBs.
>
Yes, I meant it doesn't completely flush the TLB as we do right now when invalidating the whole VPID.
Tamas
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