[PATCH v2 10/20] x86/sev: Use non-instrumented bitops in the GHCB accessors

[PATCH v2 10/20] x86/sev: Use non-instrumented bitops in the GHCB accessors

[Sasha Levin]

The GHCB accessors are used from noinstr code, such as
__sev_es_nmi_complete(), but use test_bit() and __set_bit(), which
call the KASAN and KCSAN checks. arch/x86/coco/sev/Makefile disables
KASAN and KCSAN for noinstr.o, which turns those checks into empty
stubs, but they still have to be inlined. Instrumentation such as gcov
can prevent that and leave calls to kasan_check_write() behind in
noinstr code.

Use the arch_ bitops, which aren't instrumented, as is done elsewhere
for noinstr code.

Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/include/asm/svm.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
index 83fd49b26a4b1..9881c702a8f01 100644
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -674,8 +674,8 @@ static inline void __unused_size_checks(void)
 #define DEFINE_GHCB_ACCESSORS(field)						\
 	static __always_inline bool ghcb_##field##_is_valid(const struct ghcb *ghcb) \
 	{									\
-		return test_bit(GHCB_BITMAP_IDX(field),				\
-				(unsigned long *)&ghcb->save.valid_bitmap);	\
+		return arch_test_bit(GHCB_BITMAP_IDX(field),			\
+				     (unsigned long *)&ghcb->save.valid_bitmap); \
 	}									\
 										\
 	static __always_inline u64 ghcb_get_##field(struct ghcb *ghcb)		\
@@ -690,8 +690,8 @@ static inline void __unused_size_checks(void)
 										\
 	static __always_inline void ghcb_set_##field(struct ghcb *ghcb, u64 value) \
 	{									\
-		__set_bit(GHCB_BITMAP_IDX(field),				\
-			  (unsigned long *)&ghcb->save.valid_bitmap);		\
+		arch___set_bit(GHCB_BITMAP_IDX(field),				\
+			       (unsigned long *)&ghcb->save.valid_bitmap);	\
 		ghcb->save.field = value;					\
 	}
 
-- 
2.53.0

Re: [PATCH v2 10/20] x86/sev: Use non-instrumented bitops in the GHCB accessors

[Sean Christopherson]

On Mon, Nov 02, 2026, Sasha Levin wrote:
> The GHCB accessors are used from noinstr code, such as
> __sev_es_nmi_complete(), but use test_bit() and __set_bit(), which
> call the KASAN and KCSAN checks. arch/x86/coco/sev/Makefile disables
> KASAN and KCSAN for noinstr.o, which turns those checks into empty
> stubs, but they still have to be inlined. Instrumentation such as gcov
> can prevent that and leave calls to kasan_check_write() behind in
> noinstr code.
> 
> Use the arch_ bitops, which aren't instrumented, as is done elsewhere
> for noinstr code.
> 
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---

Reviewed-by: Sean Christopherson <seanjc@google.com>