linux-kernel - Re: [PATCH 30/30] mm/mmap: Drop ARCH_HAS_VM_GET_PAGE

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Date:   Mon, 14 Feb 2022 15:29:01 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-arch@...r.kernel.org
Subject: Re: [PATCH 30/30] mm/mmap: Drop ARCH_HAS_VM_GET_PAGE_PROT



On 2/14/22 3:18 PM, Geert Uytterhoeven wrote:
> Hi Anshuman,
> 
> On Mon, Feb 14, 2022 at 7:54 AM Anshuman Khandual
> <anshuman.khandual@....com> wrote:
>> All platforms now define their own vm_get_page_prot() and also there is no
>> generic version left to fallback on. Hence drop ARCH_HAS_GET_PAGE_PROT.
>>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: linux-mm@...ck.org
>> Cc: linux-kernel@...r.kernel.org
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> 
> Thanks for your patch!
> 
>> -       select ARCH_HAS_VM_GET_PAGE_PROT
> 
> So before, all architectures selected ARCH_HAS_VM_GET_PAGE_PROT...

Right. ARCH_HAS_VM_GET_PAGE_PROT construct is required until all platforms
define their own vm_get_page_prot(). But once defined, this can be dropped
off, as a generic MM fallback is no longer available otherwise.

> 
>> --- a/mm/mmap.c
>> +++ b/mm/mmap.c
>> @@ -81,7 +81,6 @@ static void unmap_region(struct mm_struct *mm,
>>                 struct vm_area_struct *vma, struct vm_area_struct *prev,
>>                 unsigned long start, unsigned long end);
>>
>> -#ifndef CONFIG_ARCH_HAS_VM_GET_PAGE_PROT
> 
> ... hence the block below was not included.
> 
>>  /* description of effects of mapping type and prot in current implementation.
>>   * this is due to the limited x86 page protection hardware.  The expected
>>   * behavior is in parens:
>> @@ -102,8 +101,6 @@ static void unmap_region(struct mm_struct *mm,
>>   *                                                             w: (no) no
>>   *                                                             x: (yes) yes
>>   */
>> -#endif /* CONFIG_ARCH_HAS_VM_GET_PAGE_PROT */
>> -
> 
> So shouldn't the whole block be removed instead?

You are right, will remove the entire comment block here.

> Do I need more coffee??
> 
>>  static pgprot_t vm_pgprot_modify(pgprot_t oldprot, unsigned long vm_flags)
>>  {
>>         return pgprot_modify(oldprot, vm_get_page_prot(vm_flags));
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds
>