Re: [PATCH v7 07/42] KVM: guest_memfd: Only prepare folios for private pages

[Ackerley Tng]

Suzuki K Poulose <suzuki.poulose@xxxxxxx> writes:

>
> [...snip...]
>
>>> @@ -914,7 +916,8 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct
>>> kvm_memory_slot *slot,
>>>           folio_mark_uptodate(folio);
>>>       }
>>> -    r = kvm_gmem_prepare_folio(kvm, slot, gfn, folio);
>>> +    if (kvm_gmem_is_private_mem(inode, index))
>>
>> Don't we need to make sure the entire folio is private ? Not just the
>> page at the index ?
>>      if (kvm_gmem_range_is_private(, index, folio_nr_pages(folio)) ?

I was thinking to fix this when I do huge pages, for now guest_memfd is
always just PAGE_SIZE, so just looking up index is fine.

Is that okay?

>
> Or rather, we should go through the individual pages and apply the
> prepare for ones that are private ?
>
> Suzuki
>

IIRC the plan was to make kvm_gmem_prepare_folio() idempotent, as in, if
a page is already private, just skip. Currently sev_gmem_prepare() does
a pr_debug(), which I guess is technically still idempotent.

I'm thinking that the information tha needs tracking to make
.gmem_prepare() idempotent should be tracked by arch code.

Does this work for ARM CCA?

>>
>> [...snip...]
>>