On Thu, Aug 17, 2017 at 03:01:31PM -0700, Ram Pai wrote:
> On Thu, Aug 17, 2017 at 05:54:45PM -0300, Thiago Jung Bauermann wrote:
[snip]
> >
> > I'm currently preparing a patch for that. One question: did I understand
> > correctly that Paul Mackerras' answer on this thread¹ means that KVM
> > doesn't need to reserve any keys for itself and can pass on 32 keys to
> > the guest?
>
> No. KVM does use key 31 for emulated MMIO.
>
> if (!(memslot && !(memslot->flags & KVM_MEMSLOT_INVALID))) {
> /* Emulated MMIO - mark this with key=31 */
> pteh |= HPTE_V_ABSENT;
> ptel |= HPTE_R_KEY_HI |
> HPTE_R_KEY_LO;
> goto do_insert;
> }
Actually, the guest *can* use all 32 keys. We only use key 31 on
absent HPTEs (see the HPTE_V_ABSENT flag above - these are HPTEs that
the guest thinks are valid but are not actually mapped in the real
HPT).
Paul.
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