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

[David Hildenbrand]

> > > 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