linux-kernel - Re: [PATCH v7 7/9] mm: Add address parameter to arch_validate

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Date:   Thu, 10 Aug 2017 08:41:41 -0600
From:   Khalid Aziz <khalid.aziz@...cle.com>
To:     Michael Ellerman <mpe@...erman.id.au>, akpm@...ux-foundation.org,
        benh@...nel.crashing.org, paulus@...ba.org, davem@...emloft.net,
        dave.hansen@...ux.intel.com
Cc:     bsingharora@...il.com, dja@...ens.net, tglx@...utronix.de,
        mgorman@...e.de, aarcange@...hat.com,
        kirill.shutemov@...ux.intel.com, heiko.carstens@...ibm.com,
        ak@...ux.intel.com, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        sparclinux@...r.kernel.org, Khalid Aziz <khalid@...ehiking.org>
Subject: Re: [PATCH v7 7/9] mm: Add address parameter to arch_validate_prot()

On 08/10/2017 07:20 AM, Michael Ellerman wrote:
> Khalid Aziz <khalid.aziz@...cle.com> writes:
> 
>> A protection flag may not be valid across entire address space and
>> hence arch_validate_prot() might need the address a protection bit is
>> being set on to ensure it is a valid protection flag. For example, sparc
>> processors support memory corruption detection (as part of ADI feature)
>> flag on memory addresses mapped on to physical RAM but not on PFN mapped
>> pages or addresses mapped on to devices. This patch adds address to the
>> parameters being passed to arch_validate_prot() so protection bits can
>> be validated in the relevant context.
>>
>> Signed-off-by: Khalid Aziz <khalid.aziz@...cle.com>
>> Cc: Khalid Aziz <khalid@...ehiking.org>
>> ---
>> v7:
>> 	- new patch
>>
>>   arch/powerpc/include/asm/mman.h | 2 +-
>>   arch/powerpc/kernel/syscalls.c  | 2 +-
>>   include/linux/mman.h            | 2 +-
>>   mm/mprotect.c                   | 2 +-
>>   4 files changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/mman.h b/arch/powerpc/include/asm/mman.h
>> index 30922f699341..bc74074304a2 100644
>> --- a/arch/powerpc/include/asm/mman.h
>> +++ b/arch/powerpc/include/asm/mman.h
>> @@ -40,7 +40,7 @@ static inline bool arch_validate_prot(unsigned long prot)
>>   		return false;
>>   	return true;
>>   }
>> -#define arch_validate_prot(prot) arch_validate_prot(prot)
>> +#define arch_validate_prot(prot, addr) arch_validate_prot(prot)
> 
> This can be simpler, as just:
> 
> #define arch_validate_prot arch_validate_prot
> 

Hi Michael,

Thanks for reviewing!

My patch expands parameter list for arch_validate_prot() from one to two 
parameters. Existing powerpc version of arch_validate_prot() is written 
with one parameter. If I use the above #define, compilation fails with:

mm/mprotect.c: In function ‘do_mprotect_pkey’:
mm/mprotect.c:399: error: too many arguments to function 
‘arch_validate_prot’

Another way to solve it would be to add the new addr parameter to 
powerpc version of arch_validate_prot() but I chose the less disruptive 
solution of tackling it through #define and expanded the existing 
#define to include the new parameter. Make sense?

Thanks,
Khalid