On Tue, 2021-03-09 at 14:12 +0100, Paolo Bonzini wrote:
> On 09/03/21 11:09, Maxim Levitsky wrote:
> > What happens if mmio generation overflows (e.g if userspace keeps on
> > updating the memslots)?
> > In theory if we have a SPTE with a stale generation, it can became valid,
> > no?
> >
> > I think that we should in the case of the overflow zap all mmio sptes.
> > What do you think?
>
> Zapping all MMIO SPTEs is done by updating the generation count. When
> it overflows, all SPs are zapped:
>
> /*
> * The very rare case: if the MMIO generation number has wrapped,
> * zap all shadow pages.
> */
> if (unlikely(gen == 0)) {
> kvm_debug_ratelimited("kvm: zapping shadow pages for
> mmio generation wraparound\n");
> kvm_mmu_zap_all_fast(kvm);
> }
>
> So giving it more bits make this more rare, at the same time having to
> remove one or two bits is not the end of the world.
This is exactly what I expected to happen, I just didn't find that code.
Thanks for explanation, and it shows that I didn't study the mmio spte
code much.
Best regards,
Maxim Levitsky
>
> Paolo
>
