linux-kernel - [PATCH 2/2] kcsan: mark !__SANITIZE_THREAD__ stub __always

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Message-ID: <20251208-gcov-inline-noinstr-v1-2-623c48ca5714@google.com>
Date: Mon, 08 Dec 2025 01:34:59 +0000
From: Brendan Jackman <jackmanb@...gle.com>
To: Andrey Ryabinin <ryabinin.a.a@...il.com>, Alexander Potapenko <glider@...gle.com>, 
	Andrey Konovalov <andreyknvl@...il.com>, Dmitry Vyukov <dvyukov@...gle.com>, 
	Vincenzo Frascino <vincenzo.frascino@....com>, Marco Elver <elver@...gle.com>, 
	Ard Biesheuvel <ardb@...nel.org>
Cc: kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org, 
	Brendan Jackman <jackmanb@...gle.com>
Subject: [PATCH 2/2] kcsan: mark !__SANITIZE_THREAD__ stub __always_inline

The x86 instrumented bitops in
include/asm-generic/bitops/instrumented-non-atomic.h are
KCSAN-instrumented via explicit calls to instrument_* functions from
include/linux/instrumented.h.

This bitops are used from noinstr code in __sev_es_nmi_complete(). This
code avoids noinstr violations by disabling __SANITIZE_THREAD__ etc for
the compilation unit.

However, when GCOV is enabled, there can still be violations caused by
the stub versions of these functions, since coverage instrumentation is
injected that causes them to be out-of-lined.

(Note: the GCOV isntrumentation itself also appears to violate noinstr
in principle, but it appears to be harmless - basically just an inc
instruction).

Fix this by just applying __always_inline.

Signed-off-by: Brendan Jackman <jackmanb@...gle.com>
---
 include/linux/kcsan-checks.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/kcsan-checks.h b/include/linux/kcsan-checks.h
index 92f3843d9ebb8177432bb4eccc151ea66d3dcbb7..cabb2ae46bdc0963bd89533777cab586ab4d5a1b 100644
--- a/include/linux/kcsan-checks.h
+++ b/include/linux/kcsan-checks.h
@@ -226,7 +226,7 @@ static inline void kcsan_end_scoped_access(struct kcsan_scoped_access *sa) { }
 #define __kcsan_disable_current kcsan_disable_current
 #define __kcsan_enable_current kcsan_enable_current_nowarn
 #else /* __SANITIZE_THREAD__ */
-static inline void kcsan_check_access(const volatile void *ptr, size_t size,
+static __always_inline void kcsan_check_access(const volatile void *ptr, size_t size,
 				      int type) { }
 static inline void __kcsan_enable_current(void)  { }
 static inline void __kcsan_disable_current(void) { }

-- 
2.50.1