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Subject: Re: [PATCH v11 3/9] powerpc: Always define MODULES_{VADDR,END}
To: Jordan Niethe <jniethe5@gmail.com>
References: <20210429031602.2606654-1-jniethe5@gmail.com>
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From: Christophe Leroy <christophe.leroy@csgroup.eu>
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Date: Mon, 3 May 2021 07:57:27 +0200
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Cc: ajd@linux.ibm.com, Nicholas Piggin <npiggin@gmail.com>, cmr@codefail.de,
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Le 03/05/2021 à 07:39, Jordan Niethe a écrit :
> On Thu, Apr 29, 2021 at 3:04 PM Christophe Leroy
> <christophe.leroy@csgroup.eu> wrote:
>>
>>
>>
>> Le 29/04/2021 à 05:15, Jordan Niethe a écrit :
>>> If MODULES_{VADDR,END} are not defined set them to VMALLOC_START and
>>> VMALLOC_END respectively. This reduces the need for special cases. For
>>> example, powerpc's module_alloc() was previously predicated on
>>> MODULES_VADDR being defined but now is unconditionally defined.
>>>
>>> This will be useful reducing conditional code in other places that need
>>> to allocate from the module region (i.e., kprobes).
>>>
>>> Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
>>> ---
>>> v10: New to series
>>> v11: - Consider more places MODULES_VADDR was being used
>>> ---
>>>    arch/powerpc/include/asm/pgtable.h    | 11 +++++++++++
>>>    arch/powerpc/kernel/module.c          |  5 +----
>>>    arch/powerpc/mm/kasan/kasan_init_32.c | 10 +++++-----
>>>    arch/powerpc/mm/ptdump/ptdump.c       |  4 ++--
>>>    4 files changed, 19 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
>>> index c6a676714f04..882fda779648 100644
>>> --- a/arch/powerpc/include/asm/pgtable.h
>>> +++ b/arch/powerpc/include/asm/pgtable.h
>>> @@ -39,6 +39,17 @@ struct mm_struct;
>>>    #define __S110      PAGE_SHARED_X
>>>    #define __S111      PAGE_SHARED_X
>>>
>>> +#ifndef MODULES_VADDR
>>> +#define MODULES_VADDR VMALLOC_START
>>> +#define MODULES_END VMALLOC_END
>>> +#endif
>>> +
>>> +#if defined(CONFIG_PPC_BOOK3S_32) && defined(CONFIG_STRICT_KERNEL_RWX)
>>
>> No no.
>>
>> TASK_SIZE > MODULES_VADDR is ALWAYS wrong, for any target, in any configuration.
>>
>> Why is it a problem to leave the test as a BUILD_BUG_ON() in module_alloc() ?
> On ppc64s, MODULES_VADDR is __vmalloc_start (a variable)  and
> TASK_SIZE depends on current.
> Also for nohash like 44x, MODULES_VADDR is defined based on high_memory.
> If I put it back in module_alloc() and wrap it with #ifdef
> CONFIG_PPC_BOOK3S_32 will that be fine?

Thinking about it once more, I think the best approach is the one taken by Nick in 
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20210502110050.324953-1-npiggin@gmail.com/

Use MODULES_VADDR/MODULES_END when it exists, use VMALLOC_START/VMALLOC_END otherwise.

I know I suggested to always define MODULES_VADDR, but maybe that's not the best solution at the end.

For kprobes, is there a way to re-use functions from modules.c in alloc_insn_page() ?

Christophe