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

["Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx>]

On Mon, Oct 07, 2019 at 03:51:58PM +0200, Ingo Molnar wrote:
> 
> * Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote:
> 
> > 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.
> 
> 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?


> 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.

-- 
 Kirill A. Shutemov