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

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Date:   Fri, 26 Mar 2021 16:42:04 +0000
From:   Sergei Trofimovich <slyfox@...too.org>
To:     Andrey Konovalov <andreyknvl@...il.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH] mm: page_alloc: ignore init_on_free=1 for page alloc

On Fri, 26 Mar 2021 16:00:34 +0100
Andrey Konovalov <andreyknvl@...il.com> wrote:

> On Fri, Mar 26, 2021 at 2:49 PM David Hildenbrand <david@...hat.com> wrote:
> >  
> > > 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.  
> 
> This is exactly how it works, see init_mem_debugging_and_hardening().
> 
> Sergei, could you elaborate more on what kind of crash this patch is
> trying to fix? Where does it happen and why?

Yeah, I see I misinterpreted page_poison=on handling and misled you all.
Something else poisons a page when it should have not. I'll answer in more
detail to Vlastimil's email upthread and will provide more detail of the
unexpected poisoning I see.

-- 

  Sergei