ARM: 9486/1: set !LPAE MAX_PHYSMEM_BITS to 32 and remove supersection mappings

An ARM randconfig with CONFIG_GET_FREE_REGION=y and CONFIG_WERROR=y
fails to build:

  include/linux/minmax.h:86:37: error: conversion from 'long long
  unsigned int' to 'resource_size_t' {aka 'unsigned int'} changes
  value from '68719476735' to '4294967295' [-Werror=overflow]

Commit 14b80582c43e ("resource: Introduce alloc_free_mem_region()")
made kernel/resource.c clamp against
(1ULL << MAX_PHYSMEM_BITS) - 1.  resource_size_t is 32-bit without
LPAE, but ARM's default MAX_PHYSMEM_BITS is 36.

That default was added by commit db57f88e4ccb ("ARM: 8411/1: Add
default SPARSEMEM settings") because several platforms needed at
least 36 physical address bits.  !LPAE could map addresses above
32 bits only through supersections.

CONFIG_IO_36, added by commit 23bdf86aa06e ("[ARM] 3377/2: add
support for intel xsc3 core"), enabled these for XSC3 I/O.  IXP23xx
placed static I/O mappings above 4GiB until its removal in 2012, and
IOP13xx ioremap()ed its PCIe windows there until its removal in 2019.
The only remaining XSC3 platform, PXA3xx, has nothing above 4GiB.

Supersection address bits overlap the descriptor domain field, so
IO_36 also renumbered the domains to make DOMAIN_IO zero.  Remove
IO_36, the alternate domain numbering, and ioremap()'s supersection
path.  Reject !LPAE ioremap ranges extending past 4GiB before
phys_addr_t truncation, drop the now-unneeded high static-mapping
exclusion, and reduce ioremap alignment from 16MiB to the 2MiB
covered by a PMD's pair of sections.

The other supersection user, create_36bit_mapping(), was added by
commit 0b7cd62ecdc1 ("[ARM] 3017/1: Add support for 36-bit addresses
to create_mapping()") for IXP2350 and carried IXP23xx's high static
mappings.  Before this change, its only remaining call path was
efi_create_mapping() -> create_mapping_late(), for an EFI runtime
region above 4GiB.

No real-world user of this !LPAE path is known.  AArch32 UEFI
requires RAM described by its memory map to be identity-mapped
during boot services, which a 32-bit virtual address space cannot
provide above 4GiB.  Systems needing wider physical addressing are
expected to use LPAE.

Remove create_36bit_mapping() and the supersection definitions.  If
firmware nevertheless advertises such a region on !LPAE,
efi_create_mapping() rejects it before __pfn_to_phys() truncates its
address to a low alias.  EFI runtime services remain disabled, but
the kernel continues to boot.  LPAE kernels are unaffected.

With no remaining !LPAE mappings above 4GiB, set MAX_PHYSMEM_BITS to
32 for !LPAE and retain 36 for LPAE, where phys_addr_t is 64-bit.

Assisted-by: Claude:claude-fable-5

Link: https://lore.kernel.org/all/3c79d2dc-8fbd-40fc-8b2d-9d1b4f8ed34e@app.fastmail.com/
Link: https://lore.kernel.org/all/CAK8P3a2MCdUbN0QSb+M3g5_6HjPsaQwtKxFjADMZWomdry4-Ww@mail.gmail.com/
Fixes: 14b80582c43e ("resource: Introduce alloc_free_mem_region()")
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

0 files changed, 0 insertions, 0 deletions