[PATCH v3 01/12] lib/kasan: introduce CONFIG_ARCH_DEFER_KASAN option

[Sabyrzhan Tasbolatov <snovitoll@gmail.com>]

Introduce CONFIG_ARCH_DEFER_KASAN to identify architectures that need
to defer KASAN initialization until shadow memory is properly set up.

Some architectures (like PowerPC with radix MMU) need to set up their
shadow memory mappings before KASAN can be safely enabled, while others
(like s390, x86, arm) can enable KASAN much earlier or even from the
beginning.

This option allows us to:
1. Use static keys only where needed (avoiding overhead)
2. Use compile-time constants for arch that don't need runtime checks
3. Maintain optimal performance for both scenarios

Architectures that need deferred KASAN should select this option.
Architectures that can enable KASAN early will get compile-time
optimizations instead of runtime checks.

Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217049
Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
---
Changes in v3:
- Introduced CONFIG_ARCH_DEFER_KASAN to control static key usage
---
 lib/Kconfig.kasan | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index f82889a830f..38456560c85 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -19,6 +19,14 @@ config ARCH_DISABLE_KASAN_INLINE
 	  Disables both inline and stack instrumentation. Selected by
 	  architectures that do not support these instrumentation types.
 
+config ARCH_DEFER_KASAN
+	bool
+	help
+	  Architectures should select this if they need to defer KASAN
+	  initialization until shadow memory is properly set up. This
+	  enables runtime control via static keys. Otherwise, KASAN uses
+	  compile-time constants for better performance.
+
 config CC_HAS_KASAN_GENERIC
 	def_bool $(cc-option, -fsanitize=kernel-address)
 
-- 
2.34.1