Re: [PATCH] KVM: x86/mmu: add lockdep check before lookup_address_in_mm()

Sean Christopherson
2022-04-27T01:16:40Z

On Tue, Apr 26, 2022, Mingwei Zhang wrote:
> > I completely agree that lookup_address() and friends are unnecessarily fragile,
> > but I think that attempting to harden them to fix this KVM bug will open a can
> > of worms and end up delaying getting KVM fixed.
>
> So basically, we need to:
> - choose perf_get_page_size() instead of using any of the
> lookup_address*() in mm.
> - add a wrapper layer to adapt: 1) irq disabling/enabling and 2) size
> -> level translation.
>
> Agree?

Drat, I didn't see that it returns the page size, not the level. That's a bit
unfortunate. It definitely makes me less averse to fixing lookup_address_in_pgd()

Hrm. I guess since we know there's at least one broken user, and in theory
fixing lookup_address_in_pgd() should do no harm to users that don't need protection,
it makes sense to just fix lookup_address_in_pgd() and see if the x86 maintainers
push back.