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Date: Thu, 22 Jan 2026 12:30:53 -0800
From: Ackerley Tng <ackerleytng@...gle.com>
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Subject: Re: [PATCH v9 07/13] KVM: guest_memfd: Add flag to remove from direct map

Nikita Kalyazin <kalyazin@...zon.com> writes:

>
> [...snip...]
>
>>>>> @@ -533,6 +580,8 @@ static void kvm_gmem_free_folio(struct folio *folio)
>>>>>         kvm_pfn_t pfn = page_to_pfn(page);
>>>>>         int order = folio_order(folio);
>>>>>
>>>>> +     kvm_gmem_folio_restore_direct_map(folio);
>>>>> +
>>>>
>>>> I can't decide if the kvm_gmem_folio_no_direct_map(folio) should be in
>>>> the caller or within kvm_gmem_folio_restore_direct_map(), since this
>>>> time it's a folio-specific property being checked.
>>>
>>> I'm tempted to keep it similar to the kvm_gmem_folio_zap_direct_map()
>>> case.  How does the fact it's a folio-speicific property change your
>>> reasoning?
>>>
>>
>> This is good too:
>>
>>    if (kvm_gmem_folio_no_direct_map(folio))
>>            kvm_gmem_folio_restore_direct_map(folio)
>
> It turns out we can't do that because folio->mapping is gone by the time
> filemap_free_folio() is called so we can't inspect the flags.  Are you
> ok with only having this check when zapping (but not when restoring)?
> Do you think we should add a comment saying it's conditional here?
>

I thought kvm_gmem_folio_no_direct_map() only reads folio->private,
which I think should still be there at the point of
filemap_free_folio().

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

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