Re: [PATCH 2/2] arm64/mm: Use CONT_SHIFT to define CONT_PTE_SHIFT

[Gavin Shan]

Hi Anshuman,

On 9/10/20 4:17 PM, Anshuman Khandual wrote:
> On 09/08/2020 12:49 PM, Gavin Shan wrote:
> > The macro CONT_PTE_SHIFT actually depends on CONT_SHIFT, which has
> > been defined in page-def.h, based on CONFIG_ARM64_CONT_SHIFT. Lets
> > reflect the dependency.
> >
> > Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
> > ---
> >   arch/arm64/include/asm/pgtable-hwdef.h | 4 +---
> >   1 file changed, 1 insertion(+), 3 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
> > index 8a399e666837..0bd9469f4323 100644
> > --- a/arch/arm64/include/asm/pgtable-hwdef.h
> > +++ b/arch/arm64/include/asm/pgtable-hwdef.h
> > @@ -81,14 +81,12 @@
> >   /*
> >    * Contiguous page definitions.
> >    */
> > +#define CONT_PTE_SHIFT		(CONT_SHIFT + PAGE_SHIFT)
> >   #ifdef CONFIG_ARM64_64K_PAGES
> > -#define CONT_PTE_SHIFT		(5 + PAGE_SHIFT)
> >   #define CONT_PMD_SHIFT		(5 + PMD_SHIFT)
> >   #elif defined(CONFIG_ARM64_16K_PAGES)
> > -#define CONT_PTE_SHIFT		(7 + PAGE_SHIFT)
> >   #define CONT_PMD_SHIFT		(5 + PMD_SHIFT)
> >   #else
> > -#define CONT_PTE_SHIFT		(4 + PAGE_SHIFT)
> >   #define CONT_PMD_SHIFT		(4 + PMD_SHIFT)
> >   #endif
> Could not a similar CONT_PMD be created from a new CONFIG_ARM64_CONT_PMD
> config option, which would help unify CONT_PMD_SHIFT here as well ?

I was thinking of it, to have CONFIG_ARM64_CONT_PMD and defined the
following macros in arch/arm64/include/asm/page-def.h:

   #define CONT_PMD_SHIFT	CONFIG_ARM64_CONT_PMD_SHIFT
   #define CONT_PMD_SIZE        (_AC(1, UL) << (CONT_PMD_SHIFT + PMD_SHIFT)
   #define CONT_PMD_MASK        (~(CONT_PMD_SIZE - 1))

PMD_SHIFT is variable because PMD could be folded into PUD or PGD,
depending on the kernel configuration. PMD_SHIFT is declared
in arch/arm64/include/asm/pgtable-types.h, which isn't supposed
to be included in "page-def.h".

So the peroper way to handle this might be drop the continuous page
macros in page-def.h and introduce the following ones into pgtable-hwdef.h.
I will post v2 to do this if it sounds good to you.

   #define CONT_PTE_SHIFT         (CONFIG_ARM64_CONT_PTE_SHIFT + PAGE_SHIFT)
   #define CONT_PMD_SHIFT         (CONFIG_ARM64_CONT_PMD_SHIFT + PMD_SHIFT)

Thanks,
Gavin