Subject: [PATCH v4 6/6] percpu/x86: Enable strict percpu checks via named AS qualifiers

From: Uros Bizjak <[email-masked]>
Date: Mon, 27 Jan 2025 17:05:10 +0100

This patch declares percpu variables in __seg_gs/__seg_fs named AS
and keeps them named AS qualified until they are dereferenced with
percpu accessor. This approach enables various compiler check
for cross-namespace variable assignments.

Signed-off-by: Uros Bizjak <[email-masked]>
Acked-by: Nadav Amit <[email-masked]>
Cc: Dennis Zhou <[email-masked]>
Cc: Tejun Heo <[email-masked]>
Cc: Christoph Lameter <[email-masked]>
Cc: Thomas Gleixner <[email-masked]>
Cc: Ingo Molnar <[email-masked]>
Cc: Borislav Petkov <[email-masked]>
Cc: Dave Hansen <[email-masked]>
Cc: "H. Peter Anvin" <[email-masked]>
Cc: Linus Torvalds <[email-masked]>
Cc: Andy Lutomirski <[email-masked]>
Cc: Brian Gerst <[email-masked]>
Cc: Peter Zijlstra <[email-masked]>
---
 arch/x86/include/asm/percpu.h | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index 27f668660abe..474d648bca9a 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -95,9 +95,18 @@
 
 #endif /* CONFIG_SMP */
 
-#define __my_cpu_type(var)	typeof(var) __percpu_seg_override
-#define __my_cpu_ptr(ptr)	(__my_cpu_type(*(ptr))*)(__force uintptr_t)(ptr)
-#define __my_cpu_var(var)	(*__my_cpu_ptr(&(var)))
+#if defined(CONFIG_USE_X86_SEG_SUPPORT) && defined(USE_TYPEOF_UNQUAL)
+# define __my_cpu_type(var)	typeof(var)
+# define __my_cpu_ptr(ptr)	(ptr)
+# define __my_cpu_var(var)	(var)
+
+# define __percpu_qual		__percpu_seg_override
+#else
+# define __my_cpu_type(var)	typeof(var) __percpu_seg_override
+# define __my_cpu_ptr(ptr)	(__my_cpu_type(*(ptr))*)(__force uintptr_t)(ptr)
+# define __my_cpu_var(var)	(*__my_cpu_ptr(&(var)))
+#endif
+
 #define __percpu_arg(x)		__percpu_prefix "%" #x
 #define __force_percpu_arg(x)	__force_percpu_prefix "%" #x
 
-- 
2.42.0