Re: [PATCHv3 02/11] arm64: Handle section maps for swapper/idmap

[Suzuki K. Poulose]

On 14/10/15 13:06, Mark Rutland wrote:
> On Wed, Oct 14, 2015 at 12:20:25PM +0100, Suzuki K. Poulose wrote:
> > We use section maps with 4K page size to create the swapper/idmaps.
> > So far we have used !64K or 4K checks to handle the case where we
> > use the section maps.
> > This patch adds a new symbol, ARM64_SWAPPER_USES_SECTION_MAPS, to
> > handle cases where we use section maps, instead of using the page size
> > symbols.
> >
> > Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> > Cc: Mark Rutland <mark.rutland@xxxxxxx>
> > Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> > Cc: Will Deacon <will.deacon@xxxxxxx>
> > Signed-off-by: Suzuki K. Poulose <suzuki.poulose@xxxxxxx>
> > ---
> >   arch/arm64/include/asm/kernel-pgtable.h |   31 ++++++++-----
> >   arch/arm64/mm/mmu.c                     |   72 ++++++++++++++-----------------
> >   2 files changed, 52 insertions(+), 51 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/kernel-pgtable.h b/arch/arm64/include/asm/kernel-pgtable.h
> > index 622929d..5876a36 100644
> > --- a/arch/arm64/include/asm/kernel-pgtable.h
> > +++ b/arch/arm64/include/asm/kernel-pgtable.h
> > @@ -19,6 +19,13 @@
> >   #ifndef __ASM_KERNEL_PGTABLE_H
> >   #define __ASM_KERNEL_PGTABLE_H
> >
> > +/* With 4K pages, we use section maps. */
> > +#ifdef CONFIG_ARM64_4K_PAGES
> > +#define ARM64_SWAPPER_USES_SECTION_MAPS 1
> > +#else
> > +#define ARM64_SWAPPER_USES_SECTION_MAPS 0
> > +#endif
>
> The comment is somewhat redunant. It would be better to state why we do
> this for 4K and not 64K (or 16K).

Something like :

/*
 * ARM64 kernel is guaranteed to be loaded at 2M aligned
 * address (as per booting requirements). Hence we can use
 * section mapping with 4K (section size = 2M) and not with
 * 16K(section size = 32M) or 64K (section size = 512M).
 */

> > +	 * us PUD_SIZE (with SECTION maps, i.e, 4K) or PMD_SIZE (without
> > +	 * SECTION maps, i.e, 64K pages) memory starting from PHYS_OFFSET
> > +	 * (which must be aligned to 2MB as per Documentation/arm64/booting.txt).
>
> This didn't seem to get updated for 16K later in the series, unless I
> missed something.
>
> Perhaps drop the mention of 4K / 64K entirely here?

You are right, I missed it. We can drop the pagesize info entirely.

> > @@ -551,7 +552,7 @@ int kern_addr_valid(unsigned long addr)
> >   	return pfn_valid(pte_pfn(*pte));
> >   }
> >   #ifdef CONFIG_SPARSEMEM_VMEMMAP
> > -#ifdef CONFIG_ARM64_64K_PAGES
> > +#if !ARM64_SWAPPER_USES_SECTION_MAPS
>
> This leaves the comments on the #else and #endif stale. Please update
> those too.

Done.

Thanks
Suzuki

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