linux-kernel - Re: [PATCH v2 5/5] mm, page_poison: remove CONFIG_PAGE_POISONING

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Date:   Wed, 11 Nov 2020 16:45:53 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Alexander Potapenko <glider@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Michal Hocko <mhocko@...nel.org>,
        Mateusz Nosek <mateusznosek0@...il.com>,
        Laura Abbott <labbott@...nel.org>
Subject: Re: [PATCH v2 5/5] mm, page_poison: remove CONFIG_PAGE_POISONING_ZERO

On 03.11.20 16:22, Vlastimil Babka wrote:
> CONFIG_PAGE_POISONING_ZERO uses the zero pattern instead of 0xAA. It was
> introduced by commit 1414c7f4f7d7 ("mm/page_poisoning.c: allow for zero
> poisoning"), noting that using zeroes retains the benefit of sanitizing content
> of freed pages, with the benefit of not having to zero them again on alloc, and
> the downside of making some forms of corruption (stray writes of NULLs) harder
> to detect than with the 0xAA pattern. Together with
> CONFIG_PAGE_POISONING_NO_SANITY it made possible to sanitize the contents on
> free without checking it back on alloc.
> 
> These days we have the init_on_free() option to achieve sanitization with
> zeroes and to save clearing on alloc (and without checking on alloc). Arguably
> if someone does choose to check the poison for corruption on alloc, the savings
> of not clearing the page are secondary, and it makes sense to always use the
> 0xAA poison pattern. Thus, remove the CONFIG_PAGE_POISONING_ZERO option for
> being redundant.

I agree, this simplifies things ... and I don't see a need to complicate 
things to speed up corner-case debug mechanisms. Thanks!

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb