linux-kernel - Re: [PATCH V4 07/26] mm/mmap: Build protect protection_map[] with ARCH_HAS_VM_GET_PAGE

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Date:   Fri, 24 Jun 2022 11:06:44 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Cc:     "hch@...radead.org" <hch@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "openrisc@...ts.librecores.org" <openrisc@...ts.librecores.org>,
        "linux-xtensa@...ux-xtensa.org" <linux-xtensa@...ux-xtensa.org>,
        "linux-csky@...r.kernel.org" <linux-csky@...r.kernel.org>,
        "linux-hexagon@...r.kernel.org" <linux-hexagon@...r.kernel.org>,
        "linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,
        "linux-alpha@...r.kernel.org" <linux-alpha@...r.kernel.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        "linux-m68k@...ts.linux-m68k.org" <linux-m68k@...ts.linux-m68k.org>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-um@...ts.infradead.org" <linux-um@...ts.infradead.org>,
        "linux-sh@...r.kernel.org" <linux-sh@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V4 07/26] mm/mmap: Build protect protection_map[] with
 ARCH_HAS_VM_GET_PAGE_PROT



On 6/24/22 10:52, Christophe Leroy wrote:
> 
> 
> Le 24/06/2022 à 06:43, Anshuman Khandual a écrit :
>> protection_map[] has already been moved inside those platforms which enable
> 
> Usually "already" means before your series.
> 
> Your series is the one that moves protection_map[] so I would have just 
> said "Now that protection_map[] has been moved inside those platforms 
> which enable ...."

Got it, will update the commit message.

> 
>> ARCH_HAS_VM_GET_PAGE_PROT. Hence generic protection_map[] array now can be
>> protected with CONFIG_ARCH_HAS_VM_GET_PAGE_PROT intead of __P000.
>>
>> 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>
>> ---
>>   include/linux/mm.h | 2 +-
>>   mm/mmap.c          | 5 +----
>>   2 files changed, 2 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 237828c2bae2..70d900f6df43 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -424,7 +424,7 @@ extern unsigned int kobjsize(const void *objp);
>>    * mapping from the currently active vm_flags protection bits (the
>>    * low four bits) to a page protection mask..
>>    */
>> -#ifdef __P000
>> +#ifndef CONFIG_ARCH_HAS_VM_GET_PAGE_PROT
>>   extern pgprot_t protection_map[16];
> 
> Is this declaration still needed ? I have the feeling that 
> protection_map[] is only used in mm/mmap.c now.

At this point generic protection_map[] array is still being used via
this declaration on many (!ARCH_HAS_VM_GET_PAGE_PROT) platforms such
as mips, m68k, arm etc.

> 
>>   #endif
>>   
>> diff --git a/mm/mmap.c b/mm/mmap.c
>> index 55c30aee3999..43db3bd49071 100644
>> --- a/mm/mmap.c
>> +++ b/mm/mmap.c
>> @@ -101,7 +101,7 @@ static void unmap_region(struct mm_struct *mm,
>>    *								w: (no) no
>>    *								x: (yes) yes
>>    */
>> -#ifdef __P000
>> +#ifndef CONFIG_ARCH_HAS_VM_GET_PAGE_PROT
>>   pgprot_t protection_map[16] __ro_after_init = {
> 
> Should this be static, as it seems to now be used only in this file ?

This is being used in some platforms as mentioned before.

> And it could also be 'const' instead of __ro_after_init.

Then should be able to be a 'const' wrt  mips, m68k, arm platforms.
But should this even be changed, if this is going to be dropped off
eventually ?

> 
>>   	[VM_NONE]					= __P000,
>>   	[VM_READ]					= __P001,
>> @@ -120,9 +120,6 @@ pgprot_t protection_map[16] __ro_after_init = {
>>   	[VM_SHARED | VM_EXEC | VM_WRITE]		= __S110,
>>   	[VM_SHARED | VM_EXEC | VM_WRITE | VM_READ]	= __S111
>>   };
>> -#endif
>> -
>> -#ifndef CONFIG_ARCH_HAS_VM_GET_PAGE_PROT
>>   DECLARE_VM_GET_PAGE_PROT
>>   #endif	/* CONFIG_ARCH_HAS_VM_GET_PAGE_PROT */
>>