linux-kernel - Re: [PATCH v2] powerpc: fix boot on BOOK3S_32 with CONFIG_STRICT_KERNEL

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Message-ID: <141a04c4-a236-430d-f346-ad31252e146a@c-s.fr>
Date:   Wed, 22 Nov 2017 08:16:28 +0100
From:   Christophe LEROY <christophe.leroy@....fr>
To:     Balbir Singh <bsingharora@...il.com>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Scott Wood <oss@...error.net>, Meelis Roos <mroos@...ux.ee>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" 
        <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v2] powerpc: fix boot on BOOK3S_32 with
 CONFIG_STRICT_KERNEL_RWX



Le 22/11/2017 à 00:07, Balbir Singh a écrit :
> On Wed, Nov 22, 2017 at 1:28 AM, Christophe Leroy
> <christophe.leroy@....fr> wrote:
>> On powerpc32, patch_instruction() is called by apply_feature_fixups()
>> which is called from early_init()
>>
>> There is the following note in front of early_init():
>>   * Note that the kernel may be running at an address which is different
>>   * from the address that it was linked at, so we must use RELOC/PTRRELOC
>>   * to access static data (including strings).  -- paulus
>>
>> Therefore, slab_is_available() cannot be called yet, and
>> text_poke_area must be addressed with PTRRELOC()
>>
>> Fixes: 37bc3e5fd764f ("powerpc/lib/code-patching: Use alternate map
>> for patch_instruction()")
>> Reported-by: Meelis Roos <mroos@...ux.ee>
>> Cc: Balbir Singh <bsingharora@...il.com>
>> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
>> ---
>>   v2: Added missing asm/setup.h
>>
>>   arch/powerpc/lib/code-patching.c | 6 ++----
>>   1 file changed, 2 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
>> index c9de03e0c1f1..d469224c4ada 100644
>> --- a/arch/powerpc/lib/code-patching.c
>> +++ b/arch/powerpc/lib/code-patching.c
>> @@ -21,6 +21,7 @@
>>   #include <asm/tlbflush.h>
>>   #include <asm/page.h>
>>   #include <asm/code-patching.h>
>> +#include <asm/setup.h>
>>
>>   static int __patch_instruction(unsigned int *addr, unsigned int instr)
>>   {
>> @@ -146,11 +147,8 @@ int patch_instruction(unsigned int *addr, unsigned int instr)
>>           * During early early boot patch_instruction is called
>>           * when text_poke_area is not ready, but we still need
>>           * to allow patching. We just do the plain old patching
>> -        * We use slab_is_available and per cpu read * via this_cpu_read
>> -        * of text_poke_area. Per-CPU areas might not be up early
>> -        * this can create problems with just using this_cpu_read()
>>           */
>> -       if (!slab_is_available() || !this_cpu_read(text_poke_area))
>> +       if (!this_cpu_read(*PTRRELOC(&text_poke_area)))
>>                  return __patch_instruction(addr, instr);
> 
> On ppc64, we call apply_feature_fixups() in early_setup() after we've
> relocated ourselves. Sorry for missing the ppc32 case. I would like to
> avoid PTRRELOC when unnecessary.

What do you suggest then ?

Some #ifdef PPC32 around that ?

Christophe


> 
> Balbir Singh.
>