Re: [PATCH v2 1/4] mm: define MAX_PTRS_PER_{PTE,PMD,PUD}

From: Christophe Leroy
Date: Tue Dec 10 2019 - 01:35:22 EST

Le 10/12/2019 Ã 05:47, Daniel Axtens a ÃcritÂ:
powerpc has boot-time configurable PTRS_PER_PTE, PMD and PUD. The
values are selected based on the MMU under which the kernel is
booted. This is much like how 4 vs 5-level paging on x86_64 leads to
boot-time configurable PTRS_PER_P4D.

So far, this hasn't leaked out of arch/powerpc. But with KASAN, we
have static arrays based on PTRS_PER_*, so for powerpc support must
provide constant upper bounds for generic code.

Define MAX_PTRS_PER_{PTE,PMD,PUD} for this purpose.

I have configured these constants:
- in asm-generic headers
- on arches that implement KASAN: x86, s390, arm64, xtensa and powerpc

I think we shoud avoid spreading default values all over the place when all arches but one uses the default.

I would drop this patch 1, squash the powerpc part of it in the last patch, and define defaults in patch 2, see my comments there.

I haven't wired up any other arches just yet - there is no user of
the constants outside of the KASAN code I add in the next patch, so
missing the constants on arches that don't support KASAN shouldn't
break anything.

Suggested-by: Christophe Leroy <christophe.leroy@xxxxxx>
Signed-off-by: Daniel Axtens <dja@xxxxxxxxxx>
arch/arm64/include/asm/pgtable-hwdef.h | 3 +++
arch/powerpc/include/asm/book3s/64/hash.h | 4 ++++
arch/powerpc/include/asm/book3s/64/pgtable.h | 7 +++++++
arch/powerpc/include/asm/book3s/64/radix.h | 5 +++++
arch/s390/include/asm/pgtable.h | 3 +++
arch/x86/include/asm/pgtable_types.h | 5 +++++
arch/xtensa/include/asm/pgtable.h | 1 +
include/asm-generic/pgtable-nop4d-hack.h | 9 +++++----
include/asm-generic/pgtable-nopmd.h | 9 +++++----
include/asm-generic/pgtable-nopud.h | 9 +++++----
10 files changed, 43 insertions(+), 12 deletions(-)