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

[Gavin Shan]

Hi Anshuman,

On 9/10/20 7:28 PM, Anshuman Khandual wrote:
> On 09/10/2020 02:01 PM, Gavin Shan wrote:
> > 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
>
> Even CONT_PMD_SHIFT via the new CONFIG_ARM64_CONT_PMD_SHIFT will
> be a variable as well depending on page size.

Yes, it depends on the variable PMD_SHIFT.

> > in arch/arm64/include/asm/pgtable-types.h, which isn't supposed
> > to be included in "page-def.h".
>
> Are there build failures if <pgtable-types.h> is included from <page-def.h> ?

Yes, something like this:

  AS      arch/arm64/kernel/head.o
In file included from ./arch/arm64/include/asm/pgtable-hwdef.h:8,
                 from ./arch/arm64/include/asm/page-def.h:12,
                 from ./arch/arm64/include/asm/page.h:11,
                 from ./arch/arm64/include/asm/proc-fns.h:14,
                 from ./arch/arm64/include/asm/pgtable.h:9,
                 from ./include/linux/pgtable.h:6,
                 from ./arch/arm64/include/asm/io.h:12,
                 from ./include/linux/io.h:13,
                 from drivers/bus/vexpress-config.c:9:
./arch/arm64/include/asm/memory.h:91:55: warning: "PAGE_SHIFT" is not defined, evaluates to 0 [-Wundef]
 #if defined(CONFIG_VMAP_STACK) && (MIN_THREAD_SHIFT < PAGE_SHIFT)
                                                       ^~~~~~~~~~
./arch/arm64/include/asm/memory.h:97:21: warning: "PAGE_SHIFT" is not defined, evaluates to 0 [-Wundef]
 #if THREAD_SHIFT >= PAGE_SHIFT
                     ^~~~~~~~~~


> > 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.
>
> Sure, go ahead if that builds. But unifying both these macros seems cleaner.

Thanks for your confirmation. v2 is on the way :)

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

Thanks,
Gavin