Re: [PATCH V4 2/2] mm/pgtable/debug: Add test validating architecture page table helpers

Anshuman Khandual
2019-10-08T08:13:12Z

On 10/07/2019 07:30 PM, Kirill A. Shutemov wrote:
> On Mon, Oct 07, 2019 at 03:51:58PM +0200, Ingo Molnar wrote:
>>
>> * Kirill A. Shutemov <kirill@shutemov.name> wrote:
>>
>>> On Mon, Oct 07, 2019 at 03:06:17PM +0200, Ingo Molnar wrote:
>>>>
>>>> * Anshuman Khandual <anshuman.khandual@arm.com> wrote:
>>>>
>>>>> This adds a test module which will validate architecture page table helpers
>>>>> and accessors regarding compliance with generic MM semantics expectations.
>>>>> This will help various architectures in validating changes to the existing
>>>>> page table helpers or addition of new ones.
>>>>>
>>>>> Test page table and memory pages creating it's entries at various level are
>>>>> all allocated from system memory with required alignments. If memory pages
>>>>> with required size and alignment could not be allocated, then all depending
>>>>> individual tests are skipped.
>>>>
>>>>> diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
>>>>> index 52e5f5f2240d..b882792a3999 100644
>>>>> --- a/arch/x86/include/asm/pgtable_64_types.h
>>>>> +++ b/arch/x86/include/asm/pgtable_64_types.h
>>>>> @@ -40,6 +40,8 @@ static inline bool pgtable_l5_enabled(void)
>>>>> #define pgtable_l5_enabled() 0
>>>>> #endif /* CONFIG_X86_5LEVEL */
>>>>>
>>>>> +#define mm_p4d_folded(mm) (!pgtable_l5_enabled())
>>>>> +
>>>>> extern unsigned int pgdir_shift;
>>>>> extern unsigned int ptrs_per_p4d;
>>>>
>>>> Any deep reason this has to be a macro instead of proper C?
>>>
>>> It's a way to override the generic mm_p4d_folded(). It can be rewritten
>>> as inline function + define. Something like:
>>>
>>> #define mm_p4d_folded mm_p4d_folded
>>> static inline bool mm_p4d_folded(struct mm_struct *mm)
>>> {
>>> return !pgtable_l5_enabled();
>>> }
>>>
>>> But I don't see much reason to be more verbose here than needed.
>>
>> C type checking? Documentation? Yeah, I know it's just a one-liner, but
>> the principle of the death by a thousand cuts applies here.
>
> Okay, if you think it worth it. Anshuman, could you fix it up for the next
> submission?

Sure, will do.

>
>
>> BTW., any reason this must be in the low level pgtable_64_types.h type
>> header, instead of one of the API level header files?
>
> I defined it next pgtable_l5_enabled(). What is more appropriate place to
> you? pgtable_64.h? Yeah, it makes sense.

Needs to be moved to arch/x86/include/asm/pgtable_64.h as well ?