Re: [PATCH 0/3] Use arch_make_folio_accessible() everywhere

[Matthew Wilcox <willy@infradead.org>]

On Fri, Sep 15, 2023 at 07:54:50PM +0200, Claudio Imbrenda wrote:
> On Fri, 15 Sep 2023 18:28:25 +0100
> "Matthew Wilcox (Oracle)" <willy@infradead.org> wrote:
> 
> > We introduced arch_make_folio_accessible() a couple of years
> > ago, and it's in use in the page writeback path.  GUP still uses
> > arch_make_page_accessible(), which means that we can succeed in making
> > a single page of a folio accessible, then fail to make the rest of the
> > folio accessible when it comes time to do writeback and it's too late
> > to do anything about it.  I'm not sure how much of a real problem this is.
> > 
> > Switching everything around to arch_make_folio_accessible() also lets
> > us switch the page flag to be per-folio instead of per-page, which is
> > a good step towards dynamically allocated folios.
> 
> if I understand correctly, this will as a matter of fact move the
> security property from pages to folios.

Correct.

> this means that trying to access a page will (try to) make the whole
> folio accessible, even though that might be counterproductive.... 
> 
> and there is no way to simply split a folio
> 
> I don't like this

As I said in the cover letter, we already make the entire folio
accessible in the writeback path.  I suppose if you never write the
folio back, this is new ...

Anyway, looking forward to a more substantial discussion on Monday.