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Subject: Re: [PATCH 1/3] mm, page_alloc: do not rely on the order of
 page_poison and init_on_alloc/free parameters
To:     Vlastimil Babka <vbabka@suse.cz>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Alexander Potapenko <glider@google.com>,
        Kees Cook <keescook@chromium.org>,
        Michal Hocko <mhocko@kernel.org>,
        Mateusz Nosek <mateusznosek0@gmail.com>
References: <20201026173358.14704-1-vbabka@suse.cz>
 <20201026173358.14704-2-vbabka@suse.cz>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <3784dac7-49cb-006b-7b9d-1244d5c59935@redhat.com>
Date:   Tue, 27 Oct 2020 10:03:34 +0100
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On 26.10.20 18:33, Vlastimil Babka wrote:
> Enabling page_poison=1 together with init_on_alloc=1 or init_on_free=1 produces
> a warning in dmesg that page_poison takes precendence. However, as these
> warnings are printed in early_param handlers for init_on_alloc/free, they are
> not printed if page_poison is enabled later on the command line (handlers are
> called in the order of their parameters), or when init_on_alloc/free is always
> enabled by the respective config option - before the page_poison early param
> handler is called, it is not considered to be enabled. This is inconsistent.
> 
> We can remove the dependency on order by making the init_on_* parameters only
> set a boolean variable, and postponing the evaluation after all early params
> have been processed. Introduce a new init_mem_debugging() function for that,
> and move the related debug_pagealloc processing there as well.

init_mem_debugging() is somewhat sub-optimal - init_on_alloc=1 or 
init_on_free=1 are rather security hardening mechanisms.

... I wondered if this could be the place to initialize any kind of mm 
parameters in the future. Like init_mem_params() or so.

> 
> As a result init_mem_debugging() knows always accurately if init_on_* and/or
> page_poison options were enabled. Thus we can also optimize want_init_on_alloc()
> and want_init_on_free(). We don't need to check page_poisoning_enabled() there,
> we can instead not enable the init_on_* tracepoint at all, if page poisoning is
> enabled. This results in a simpler and more effective code.

LGTM

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb