[PATCH v4 35/61] arm64: pgtable: Decouple PGDIR size macros from PGD/PUD/PMD levels

[Catalin Marinas]

On Thu, Oct 19, 2023 at 05:34:33PM +0100, Catalin Marinas wrote:
> On Tue, Sep 12, 2023 at 02:16:25PM +0000, Ard Biesheuvel wrote:
> > diff --git a/arch/arm64/include/asm/kernel-pgtable.h b/arch/arm64/include/asm/kernel-pgtable.h
> > index 742a4b2778f7..5000f38ae0c6 100644
> > --- a/arch/arm64/include/asm/kernel-pgtable.h
> > +++ b/arch/arm64/include/asm/kernel-pgtable.h
> > @@ -13,27 +13,22 @@
> >  #include <asm/sparsemem.h>
> >  
> >  /*
> > - * The linear mapping and the start of memory are both 2M aligned (per
> > - * the arm64 booting.txt requirements). Hence we can use section mapping
> > - * with 4K (section size = 2M) but not with 16K (section size = 32M) or
> > - * 64K (section size = 512M).
> > + * The physical and virtual addresses of the start of the kernel image are
> > + * equal modulo 2 MiB (per the arm64 booting.txt requirements). Hence we can
> > + * use section mapping with 4K (section size = 2M) but not with 16K (section
> > + * size = 32M) or 64K (section size = 512M).
> >   */
> > -
> > -/*
> > - * The idmap and swapper page tables need some space reserved in the kernel
> > - * image. Both require pgd, pud (4 levels only) and pmd tables to (section)
> > - * map the kernel. With the 64K page configuration, swapper and idmap need to
> > - * map to pte level. The swapper also maps the FDT (see __create_page_tables
> > - * for more information). Note that the number of ID map translation levels
> > - * could be increased on the fly if system RAM is out of reach for the default
> > - * VA range, so pages required to map highest possible PA are reserved in all
> > - * cases.
> > - */
> > -#ifdef CONFIG_ARM64_4K_PAGES
> > -#define SWAPPER_PGTABLE_LEVELS	(CONFIG_PGTABLE_LEVELS - 1)
> > +#if defined(PMD_SIZE) && PMD_SIZE <= MIN_KIMG_ALIGN
> 
> Nitpick: we always have PMD_SIZE defined, either directly in the arm64
> headers if we have more than 2 levels or included from the generic
> pgtable-nopmd.h. Otherwise the logic is fine.

I pushed a patch removing this defined(PMD_SIZE) but it turns out that
we include this file in assembly and while the generic PMD_SIZE is only
defined if !defined(__ASSEMBLY__). Not sure the macro is used or just
the linker complaining.

I'll revert my patch temporarily on top of for-next/core and think about
it tomorrow. I don't like that this #if check is only false because some
other header bracketed it with #ifndef __ASSEMBLY__.

-- 
Catalin