Re: Questions about the real mode in kvm/qemu

[Li Qiang <liq3ea@gmail.com>]

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Paolo Bonzini <pbonzini@redhat.com> 于2019年9月26日周四 下午5:18写道：

> On 26/09/19 10:59, Maxim Levitsky wrote:
> > If you mean to ask if there is a way to let guest access use no
> > paging at all, that is access host physical addresses directly, then
> > indeed there is no way, since regular non 'unrestricted guest' mode
> > required both protected mode and paging, and 'unrestricted guest'
> > requires EPT. Academically speaking it is of course possible to
> > create paging tables that are 1:1...
>
> Not so academically, it's exactly what KVM does.  However, indeed it
> would also be possible to switch out of EPT mode when CR0.PG=0.  I'm not
> sure why it was done this way, maybe when the code was written it was
> simpler to use the identity map.
>


Hi Paolo, what's the meaning of 'switch out of EPT mode'. Do you mean when
the guest in real mode emulation(vm86)
can do something to disable EPT? I don't find the code. Seems my
understanding is wrong.

Thanks,
Li Qiang



>
> Let's see if Avi is listening... :)
>
> Paolo
>

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