Re: [PATCH 03/15] arm64: Introduce helpers for page table levels

[Suzuki K. Poulose]

On 07/10/15 09:26, Christoffer Dall wrote:
> Hi Suzuki,
>
> On Tue, Sep 15, 2015 at 04:41:12PM +0100, Suzuki K. Poulose wrote:
> > From: "Suzuki K. Poulose" <suzuki.poulose@xxxxxxx>
> >
> > Introduce helpers for finding the number of page table
> > levels required for a given VA width, shift for a particular
> > page table level.
> >
> > Convert the existing users to the new helpers. More users
> > to follow.
> >
> > 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>
> > Reviewed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> > Tested-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> > ---
> >   arch/arm64/include/asm/pgtable-hwdef.h |   15 ++++++++++++---
> >   1 file changed, 12 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
> > index 24154b0..ce18389 100644
> > --- a/arch/arm64/include/asm/pgtable-hwdef.h
> > +++ b/arch/arm64/include/asm/pgtable-hwdef.h
> > @@ -16,13 +16,21 @@
> >   #ifndef __ASM_PGTABLE_HWDEF_H
> >   #define __ASM_PGTABLE_HWDEF_H
> >
> > +/*
> > + * Number of page-table levels required to address 'va_bits' wide
> > + * address, without section mapping
> > + */
> > +#define ARM64_HW_PGTABLE_LEVELS(va_bits) (((va_bits) - 4) / (PAGE_SHIFT - 3))
>
> I don't understand the '(va_bits) - 4' here, can you explain it (and add a
> comment to that effect) ?

As mentioned, I will change it to DIV_ROUND_UP() as suggested by Marc.

> > +#define ARM64_HW_PGTABLE_LEVEL_SHIFT(level) \
> > +		((PAGE_SHIFT - 3) * (level) + 3)
> > +
>
> While this change is clearly correct, if you can explain the math here
> in a comment as well, that would be helpful.

Sure, will add a comment to that effect.

Suzuki

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/