[PATCH v4 0/9] kasan: unify kasan_arch_is_ready() 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

This series implements two-level approach:
1. kasan_enabled() - compile-time check for KASAN configuration
2. kasan_shadow_initialized() - runtime check for shadow memory readiness

Changes in v4:
- Unified patches where ARCH_DEFER_KASAN is introduced and used
  in the KASAN code (Andrey Ryabinin)
- Fixed kasan_enable() for HW_TAGS mode (Andrey Ryabinin)
- Replaced !kasan_enabled() with !kasan_shadow_initialized() in
  loongarch which selects ARCH_DEFER_KASAN (Andrey Ryabinin)
- Addressed the issue in UML arch, where kasan_init_generic() is
  called before jump_label_init() (Andrey Ryabinin)

Adding in TO additional recipients who developed KASAN in LoongArch, UML.

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

- um - selects ARCH_DEFER_KASAN
Built defconfig with KASAN_INLINE - OK
Built defconfig with STATIC_LINK && KASAN_OUTLINE - OK
Booted ./linux - OK

- 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().

- arm64
Built defconfig, kvm_guest.config with HW_TAGS, SW_TAGS, GENERIC - OK
KASAN_KUNIT_TEST - OK
Booted via qemu-system-arm64 - OK

- x86_64
Built defconfig, kvm_guest.config with KASAN_GENERIC - OK
KASAN_KUNIT_TEST - OK
Booted via qemu-system-x86 - OK

- s390, riscv, xtensa, arm
Built defconfig with KASAN_GENERIC - OK

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/

Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217049

Sabyrzhan Tasbolatov (9):
  kasan: introduce ARCH_DEFER_KASAN and unify static key across modes
  kasan/powerpc: select ARCH_DEFER_KASAN and call kasan_init_generic
  kasan/arm,arm64: call kasan_init_generic in kasan_init
  kasan/xtensa: call kasan_init_generic in kasan_init
  kasan/loongarch: select ARCH_DEFER_KASAN and call kasan_init_generic
  kasan/um: select ARCH_DEFER_KASAN and call kasan_init_generic
  kasan/x86: call kasan_init_generic in kasan_init
  kasan/s390: call kasan_init_generic in kasan_init
  kasan/riscv: 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                   | 12 ++++++--
 arch/x86/mm/kasan_init_64.c            |  2 +-
 arch/xtensa/mm/kasan_init.c            |  2 +-
 include/linux/kasan-enabled.h          | 36 +++++++++++++++++-----
 include/linux/kasan.h                  | 42 ++++++++++++++++++++------
 lib/Kconfig.kasan                      |  8 +++++
 mm/kasan/common.c                      | 18 +++++++----
 mm/kasan/generic.c                     | 23 ++++++++------
 mm/kasan/hw_tags.c                     |  9 +-----
 mm/kasan/kasan.h                       | 36 ++++++++++++++++------
 mm/kasan/shadow.c                      | 32 +++++---------------
 mm/kasan/sw_tags.c                     |  4 ++-
 mm/kasan/tags.c                        |  2 +-
 27 files changed, 157 insertions(+), 124 deletions(-)

-- 
2.34.1