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

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Excerpts from Nicholas Piggin's message of June 24, 2021 7:57 pm:
> Excerpts from Paolo Bonzini's message of June 24, 2021 7:42 pm:
>> On 24/06/21 10:52, Nicholas Piggin wrote:
>>>> For now, wrap all calls to gfn_to_pfn functions in the new helper
>>>> function. Callers which don't need the page struct will be updated in
>>>> follow-up patches.
>>> Hmm. You mean callers that do need the page will be updated? Normally
>>> if there will be leftover users that don't need the struct page then
>>> you would go the other way and keep the old call the same, and add a new
>>> one (gfn_to_pfn_page) just for those that need it.
>> Needing kvm_pfn_page_unwrap is a sign that something might be buggy, so 
>> it's a good idea to move the short name to the common case and the ugly 
>> kvm_pfn_page_unwrap(gfn_to_pfn(...)) for the weird one.  In fact I'm not 
>> sure there should be any kvm_pfn_page_unwrap in the end.
> 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. And are gfn_to_page cases also
vulernable to the same issue?

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.


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