RFC arm64: mm: Map fixmap page tables read-only

From: Ard Biesheuvel <[email protected]>

This v2 now covers intermediate level page tables as well as the PTE level page table for the fixmap. The latter is a special case, as it

a) is only accessed via the kernel image's mapping, and never via the linear map (except for ptdump etc)

b) must be accessible via a read-write mapping, as all manipulation of read-only page table descriptors relies on the fixmap itself

and so it is treated separately. The intermediate page tables may be shared with other mappings in the upper kernel/vmalloc region, so they must be updatable using the ordinary APIs.

Build tested and boot tested on a Lenovo Yoga C630 using 16k pages.

v1: https://lore.kernel.org/all/[email protected]/

Ard Biesheuvel (4):
arm64: mm: Map fixmap PTE tables r/o in the linear map
arm64: mm: Use fault handler to permit swapper_pg_dir updates
arm64: mm: Create r/o page table region that permits updates
arm64: mm: Move fixmap intermediate page tables into .rodata

 arch/arm64/include/asm/fixmap.h  |  4 ++
 arch/arm64/include/asm/linkage.h |  1 +
 arch/arm64/include/asm/pgtable.h | 55 ++++++++------------
 arch/arm64/kernel/vmlinux.lds.S  |  6 +++
 arch/arm64/mm/fixmap.c           | 12 +++--
 arch/arm64/mm/mmu.c              | 48 +++++++++++++----
 6 files changed, 78 insertions(+), 48 deletions(-)

2.55.0.887.g758fc8c411-goog