[PATCH v5 0/2] kasan: unify kasan_enabled() and remove arch-specific implementations

[Sabyrzhan Tasbolatov <snovitoll@gmail.com>]

This patch series addresses the fragmentation in KASAN initialization
across architectures by introducing a unified approach that eliminates
duplicate static keys and arch-specific kasan_arch_is_ready()
implementations.

The core issue is that different architectures have inconsistent approaches
to KASAN readiness tracking:
- PowerPC, LoongArch, and UML arch, each implement own kasan_arch_is_ready()
- Only HW_TAGS mode had a unified static key (kasan_flag_enabled)
- Generic and SW_TAGS modes relied on arch-specific solutions
  or always-on behavior

Changes in v5:
- Unified patches where arch (powerpc, UML, loongarch) selects
  ARCH_DEFER_KASAN in the first patch not to break
  bisectability. So in v5 we have 2 patches now in the series instead of 9.
- Removed kasan_arch_is_ready completely as there is no user
- Removed __wrappers in v4, left only those where it's necessary
  due to different implementations

Tested on:
- powerpc - selects ARCH_DEFER_KASAN
Built ppc64_defconfig (PPC_BOOK3S_64) - OK
Booted via qemu-system-ppc64 - OK

I have not tested in v4 powerpc without KASAN enabled.

In v4 arch/powerpc/Kconfig it was:
	select ARCH_DEFER_KASAN			if PPC_RADIX_MMU

and compiling with ppc64_defconfig caused:
  lib/stackdepot.o:(__jump_table+0x8): undefined reference to `kasan_flag_enabled'

I have fixed it in v5 via adding KASAN condition:
	select ARCH_DEFER_KASAN			if KASAN && PPC_RADIX_MMU

- um - selects ARCH_DEFER_KASAN

KASAN_GENERIC && KASAN_INLINE && STATIC_LINK
	Before:
		In file included from mm/kasan/common.c:32:
		mm/kasan/kasan.h:550:2: error: #error kasan_arch_is_ready only works in KASAN generic outline mode!
		550 | #error kasan_arch_is_ready only works in KASAN generic outline mode

	After (with auto-selected ARCH_DEFER_KASAN):
		./arch/um/include/asm/kasan.h:29:2: error: #error UML does not work in KASAN_INLINE mode with STATIC_LINK enabled!
		29 | #error UML does not work in KASAN_INLINE mode with STATIC_LINK enabled!

KASAN_GENERIC && KASAN_OUTLINE && STATIC_LINK && 
	Before:
		./linux boots.

	After (with auto-selected ARCH_DEFER_KASAN):
		./linux boots.

KASAN_GENERIC && KASAN_OUTLINE && !STATIC_LINK
	Before:
		./linux boots

	After (with auto-disabled !ARCH_DEFER_KASAN):
		./linux boots

- loongarch - selects ARCH_DEFER_KASAN
Built defconfig with KASAN_GENERIC - OK
Haven't tested the boot. Asking Loongarch developers to verify - N/A
But should be good, since Loongarch does not have specific "kasan_init()"
call like UML does. It selects ARCH_DEFER_KASAN and calls kasan_init()
in the end of setup_arch() after jump_label_init().

Previous v4 thread: https://lore.kernel.org/all/20250805142622.560992-1-snovitoll@gmail.com/
Previous v3 thread: https://lore.kernel.org/all/20250717142732.292822-1-snovitoll@gmail.com/
Previous v2 thread: https://lore.kernel.org/all/20250626153147.145312-1-snovitoll@gmail.com/

Sabyrzhan Tasbolatov (2):
  kasan: introduce ARCH_DEFER_KASAN and unify static key across modes
  kasan: call kasan_init_generic in kasan_init

 arch/arm/mm/kasan_init.c               |  2 +-
 arch/arm64/mm/kasan_init.c             |  4 +---
 arch/loongarch/Kconfig                 |  1 +
 arch/loongarch/include/asm/kasan.h     |  7 ------
 arch/loongarch/mm/kasan_init.c         |  8 +++----
 arch/powerpc/Kconfig                   |  1 +
 arch/powerpc/include/asm/kasan.h       | 12 ----------
 arch/powerpc/mm/kasan/init_32.c        |  2 +-
 arch/powerpc/mm/kasan/init_book3e_64.c |  2 +-
 arch/powerpc/mm/kasan/init_book3s_64.c |  6 +----
 arch/riscv/mm/kasan_init.c             |  1 +
 arch/s390/kernel/early.c               |  3 ++-
 arch/um/Kconfig                        |  1 +
 arch/um/include/asm/kasan.h            |  5 ++--
 arch/um/kernel/mem.c                   | 10 ++++++--
 arch/x86/mm/kasan_init_64.c            |  2 +-
 arch/xtensa/mm/kasan_init.c            |  2 +-
 include/linux/kasan-enabled.h          | 32 ++++++++++++++++++--------
 include/linux/kasan.h                  |  6 +++++
 lib/Kconfig.kasan                      |  8 +++++++
 mm/kasan/common.c                      | 17 ++++++++++----
 mm/kasan/generic.c                     | 19 +++++++++++----
 mm/kasan/hw_tags.c                     |  9 +-------
 mm/kasan/kasan.h                       |  8 ++++++-
 mm/kasan/shadow.c                      | 12 +++++-----
 mm/kasan/sw_tags.c                     |  1 +
 mm/kasan/tags.c                        |  2 +-
 27 files changed, 107 insertions(+), 76 deletions(-)

-- 
2.34.1