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Message-ID: <CAHD1Q_wQrnSEGOvbCi0uhHZ5bRf=inzPdOhGKJ9PkVms5GSWRA@mail.gmail.com>
Date: Tue, 20 Oct 2020 17:19:42 -0300
From: Guilherme Piccoli <gpiccoli@...onical.com>
To: David Hildenbrand <david@...hat.com>
Cc: Michal Hocko <mhocko@...e.com>, Mike Kravetz <mike.kravetz@...cle.com>, linux-mm@...ck.org,
kernel-hardening@...ts.openwall.com, linux-hardening@...r.kernel.org,
linux-security-module@...r.kernel.org,
"Guilherme G. Piccoli" <kernel@...ccoli.net>,
Thadeu Lima de Souza Cascardo <cascardo@...onical.com>, Alexander Potapenko <glider@...gle.com>,
James Morris <jamorris@...ux.microsoft.com>, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] mm, hugetlb: Avoid double clearing for hugetlb pages
When I first wrote that, the design was a bit different, the flag was
called __GFP_HTLB_PAGE or something like that. The design was to
signal/mark the composing pages of hugetlb as exactly this: they are
pages composing a huge page of hugetlb "type". Then, I skipped the
"init_on_alloc" thing for such pages.
If your concern is more about semantics (or giving multiple users,
like drivers, the power to try "optimize" their code and skip this
security feature), I think my first approach was better! This way, the
flag would be restricted to hugetlb usage only.
I've changed my mind about that approach before submitting for 2 reasons:
(a) It feels a waste of resources having a GFP flag *only* to signal
regular pages composing hugetlb pages, it's a single user only,
forever!
(b) Having 2 conditional settings on __GFP_BITS_SHIFT (LOCKDEP and
HUGETLB) started to make this define a bit tricky to code, since we'd
have 2 Kconfig-conditional bits to be set.
So, I've moved to this other approach, hereby submitted.
Cheers,
Guilherme
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