Re: [PATCH 2/6] KVM: mmu: also return page from gfn_to_pfn

[Paolo Bonzini]

On 24/06/21 12:17, Nicholas Piggin wrote:
> > If all callers were updated that is one thing, but from the changelog
> > it sounds like that would not happen and there would be some gfn_to_pfn
> > users left over.
> >
> > But yes in the end you would either need to make gfn_to_pfn never return
> > a page found via follow_pte, or change all callers to the new way. If
> > the plan is for the latter then I guess that's fine.
>
> Actually in that case anyway I don't see the need -- the existence of
> gfn_to_pfn is enough to know it might be buggy. It can just as easily
> be grepped for as kvm_pfn_page_unwrap.

Sure, but that would leave us with longer function names 
(gfn_to_pfn_page* instead of gfn_to_pfn*).  So the "safe" use is the one 
that looks worse and the unsafe use is the one that looks safe.

> And are gfn_to_page cases also
> vulernable to the same issue?

No, they're just broken for the VM_IO|VM_PFNMAP case.

Paolo

> So I think it could be marked deprecated or something if not everything
> will be converted in the one series, and don't need to touch all that
> arch code with this patch.