linux-kernel - Re: [PATCH] mm: page_alloc: ignore init_on

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Date:   Fri, 26 Mar 2021 14:48:50 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Sergei Trofimovich <slyfox@...too.org>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>,
        Andrey Konovalov <andreyknvl@...il.com>
Subject: Re: [PATCH] mm: page_alloc: ignore init_on_free=1 for page alloc

On 26.03.21 12:26, Sergei Trofimovich wrote:
> init_on_free=1 does not guarantee that free pages contain only zero bytes.
> 
> Some examples:
> 1. page_poison=on takes presedence over init_on_alloc=1 / ini_on_free=1

s/ini_on_free/init_on_free/

> 2. free_pages_prepare() always poisons pages:
> 
>         if (want_init_on_free())
>             kernel_init_free_pages(page, 1 << order);
>         kernel_poison_pages(page, 1 << order

In next/master, it's the other way around already.

commit 855a9c4018f3219db8be7e4b9a65ab22aebfde82
Author: Andrey Konovalov <andreyknvl@...il.com>
Date:   Thu Mar 18 17:01:40 2021 +1100

     kasan, mm: integrate page_alloc init with HW_TAGS


> 
> I observed use of poisoned pages as the crash on ia64 booted with
> init_on_free=1 init_on_alloc=1 (CONFIG_PAGE_POISONING=y config).
> There pmd page contained 0xaaaaaaaa poison pages and led to early crash.
> 
> The change drops the assumption that init_on_free=1 guarantees free
> pages to contain zeros.
> 
> Alternative would be to make interaction between runtime poisoning and
> sanitizing options and build-time debug flags like CONFIG_PAGE_POISONING
> more coherent. I took the simpler path.
> 

I thought latest work be Vlastimil tried to tackle that. To me, it feels 
like page_poison=on  and init_on_free=1 should bail out and disable one 
of both things. Having both at the same time doesn't sound helpful.

> Tested the fix on rx3600.

Fixes: ?


-- 
Thanks,

David / dhildenb