Re: [PATCH v3 2/5] mm/mseal: update madvise() logic

[David Hildenbrand <david@redhat.com>]

>>> So - we explicitly disallow FOLL_FORCE write override for CoW file-backed
>>> mappings.
>>>
>>> Obviously if FOLL_FORCE is not set, then we're ALSO not allowed to get past a
>>> FOLL_WRITE and !VM_WRITE situation.
>>>
>>>>
>>>>>
>>>>> Hmm maybe I'll soften on this anon_vma idea then. Maybe it is a 'cheap fix' to
>>>>> rule out the _usual_ cases.
>>>>
>>>> Yeah, something to evaluate.
>>>
>>> I'm thinking more and more we're probably actually safe with !vma->anon_vma ||
>>> !(vma->vm_flags & VM_MAYWRITE).
>>
>> I think there are possible races, the question is how much you care about
>> them.
> 
> Yes I was just wrong. Please just disregard.
> 
> I mean racing with MADV_POPULATE_WRITE seems a niche thing to worry about, and
> so what if you did, it's writing a... copy of the underlying file-backed folios
> no?

MADV_POPULATE_WRITE does not apply. It's only racing with FOLL_FORCE, 
like debugger access.

Again, a race one probably shouldn't worry about in the context of mseal.

-- 
Cheers,

David / dhildenb