[RFC PATCH v2 4/4] percpu/x86: Enable strict percpu checks via named AS qualifiers

[Uros Bizjak <ubizjak@gmail.com>]

Declare percpu variables in __seg_gs/__seg_fs named AS and keep
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 <ubizjak@gmail.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
---
 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 4ab4ad60d767..b54119398c4b 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(CONFIG_CC_HAS_TYPEOF_UNQUAL)
+# define __my_cpu_type(var)	typeof(var)
+# define __my_cpu_ptr(ptr)	(ptr)
+# define __my_cpu_var(var)	(var)
+
+# define __per_cpu_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
 
-- 
2.46.0