linux-kernel - Re: [PATCH] powerpc/mm/32s: only use MMU to mark initmem NX if STRICT_KERNEL

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Message-ID: <7dd94b1c-08cb-c6ac-83c1-5b67a3dad2d8@c-s.fr>
Date:   Sun, 16 Jun 2019 10:06:14 +0200
From:   christophe leroy <christophe.leroy@....fr>
To:     Andreas Schwab <schwab@...ux-m68k.org>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        j.neuschaefer@....net, Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH] powerpc/mm/32s: only use MMU to mark initmem NX if
 STRICT_KERNEL_RWX



Le 15/06/2019 à 16:36, Andreas Schwab a écrit :
> On Jun 15 2019, Christophe Leroy <christophe.leroy@....fr> wrote:
> 
>> Andreas Schwab <schwab@...ux-m68k.org> a écrit :
>>
>>> If STRICT_KERNEL_RWX is disabled, never use the MMU to mark initmen
>>> nonexecutable.
>>
>> I dont understand, can you elaborate ?
> 
> It breaks suspend.

Ok, but we need to explain why it breaks suspend, and again your patch 
is wrong anyway because that area of memory is mapped with BATs so you 
can't use change_page_attr()

> 
>> This area is mapped with BATs so using change_page_attr() is pointless.
> 
> There must be a reason STRICT_KERNEL_RWX is not available with
> HIBERNATE.

Yes but HIBERNATE and suspend are not the same thing. I guess HIBERNATE 
is not available with STRICT_KERNEL_RWX because HIBERNATE have to write 
back saved state into read-only memory as well.

Christophe

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