linux-kernel - Re: [PATCH v2 00/15] init_mm: cleanup ARCH's text/data/brk setup code

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Date:   Mon, 7 Jun 2021 16:30:40 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Mike Rapoport <rppt@...nel.org>
CC:     <uclinux-h8-devel@...ts.sourceforge.jp>,
        <linux-s390@...r.kernel.org>, <linux-sh@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-csky@...r.kernel.org>,
        <linux-mm@...ck.org>, <linux-m68k@...ts.linux-m68k.org>,
        <openrisc@...ts.librecores.org>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        <linux-snps-arc@...ts.infradead.org>,
        <linuxppc-dev@...ts.ozlabs.org>, <linux-riscv@...ts.infradead.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 00/15] init_mm: cleanup ARCH's text/data/brk setup code


On 2021/6/7 13:48, Christophe Leroy wrote:
> Hi Kefeng,
>
> Le 07/06/2021 à 02:55, Kefeng Wang a écrit :
>>
>> On 2021/6/7 5:29, Mike Rapoport wrote:
>>> Hello Kefeng,
>>>
>>> On Fri, Jun 04, 2021 at 03:06:18PM +0800, Kefeng Wang wrote:
>>>> Add setup_initial_init_mm() helper, then use it
>>>> to cleanup the text, data and brk setup code.
>>>>
>>>> v2:
>>>> - change argument from "char *" to "void *" setup_initial_init_mm()
>>>>    suggested by Geert Uytterhoeven
>>>> - use NULL instead of (void *)0 on h8300 and m68k
>>>> - collect ACKs
>>>>
>>>> Cc: linux-snps-arc@...ts.infradead.org
>>>> Cc: linux-arm-kernel@...ts.infradead.org
>>>> Cc: linux-csky@...r.kernel.org
>>>> Cc: uclinux-h8-devel@...ts.sourceforge.jp
>>>> Cc: linux-m68k@...ts.linux-m68k.org
>>>> Cc: openrisc@...ts.librecores.org
>>>> Cc: linuxppc-dev@...ts.ozlabs.org
>>>> Cc: linux-riscv@...ts.infradead.org
>>>> Cc: linux-sh@...r.kernel.org
>>>> Cc: linux-s390@...r.kernel.org
>>>> Kefeng Wang (15):
>>>>    mm: add setup_initial_init_mm() helper
>>>>    arc: convert to setup_initial_init_mm()
>>>>    arm: convert to setup_initial_init_mm()
>>>>    arm64: convert to setup_initial_init_mm()
>>>>    csky: convert to setup_initial_init_mm()
>>>>    h8300: convert to setup_initial_init_mm()
>>>>    m68k: convert to setup_initial_init_mm()
>>>>    nds32: convert to setup_initial_init_mm()
>>>>    nios2: convert to setup_initial_init_mm()
>>>>    openrisc: convert to setup_initial_init_mm()
>>>>    powerpc: convert to setup_initial_init_mm()
>>>>    riscv: convert to setup_initial_init_mm()
>>>>    s390: convert to setup_initial_init_mm()
>>>>    sh: convert to setup_initial_init_mm()
>>>>    x86: convert to setup_initial_init_mm()
>>> I might be missing something, but AFAIU the init_mm.start_code and 
>>> other
>>> fields are not used really early so the new setup_initial_init_mm()
>>> function can be called in the generic code outside setup_arch(), e.g in
>>> mm_init().
>>
>> Hi Mike， each architecture has their own value, not the same, eg m68K 
>> and
>>
>> h8300, also the name of the text/code/brk is different in some arch, 
>> so I keep
>>
>> unchanged.
>
> What you could do is to define a __weak function that architectures 
> can override and call that function from mm_init() as suggested by Mike,
>
> Something like:
>
> void __weak setup_initial_init_mm(void)
> {
>     init_mm.start_code = (unsigned long)_stext;
>     init_mm.end_code = (unsigned long)_etext;
>     init_mm.end_data = (unsigned long)_edata;
>     init_mm.brk = (unsigned long)_end;
> }
>
> Then only the few architecture that are different would override it.
>
> I see a few archictectures are usigne PAGE_OFFSET to set .start_code, 
> but it is likely that this is equivalent to _stext.


Yes,  the __weak function is option, but the change is only covered 14 
archs, there are 7 other archs（alpha  hexagon  ia64

microblaze  mips sparc  um xtensa）without related setup code. Also like 
x86, it has own brk , maybe there are some

other different in some arch, so I think let's keep unchanged for now,  
thanks.

>
> Christophe
> .
>