Re: [PATCH v7 7/9] mm: Add address parameter to arch_validate_prot()

[Khalid Aziz <khalid.aziz@oracle.com>]

On 08/14/2017 11:02 PM, Michael Ellerman wrote:
> Khalid Aziz <khalid.aziz@oracle.com> writes:
> 
>> On 08/10/2017 07:20 AM, Michael Ellerman wrote:
>>> Khalid Aziz <khalid.aziz@oracle.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@oracle.com>
>>>> Cc: Khalid Aziz <khalid@gonehiking.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?
> 
> Yes, it makes sense. But it's a bit gross.
> 
> At first glance it looks like our arch_validate_prot() has an incorrect
> signature.
> 
> I'd prefer you just updated it to have the correct signature, I think
> you'll have to change one more line in do_mmap2(). So it's not very
> intrusive.

Thanks, Michael. I can do that.

--
Khalid