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

[Kirill A. Shutemov]

On Mon, Oct 07, 2019 at 03:06:17PM +0200, Ingo Molnar wrote:
> 
> * Anshuman Khandual <anshuman.khandual@xxxxxxx> 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.

-- 
 Kirill A. Shutemov