x86/percpu: Use __force to cast from __percpu address space

JIRA: https://issues.redhat.com/browse/RHEL-68940

commit a55c1fd
Author: Uros Bizjak <ubizjak@gmail.com>
Date:   Tue, 2 Apr 2024 19:50:38 +0200

    x86/percpu: Use __force to cast from __percpu address space

    Fix Sparse warning when casting from __percpu address space by using
    __force in the cast. x86 named address spaces are not considered to
    be subspaces of the generic (flat) address space, so explicit casts
    are required to convert pointers between these address spaces and the
    generic address space (the application should cast to uintptr_t and
    apply the segment base offset). The cast to uintptr_t removes
    __percpu address space tag and Sparse reports:

      warning: cast removes address space '__percpu' of expression

    Use __force to inform Sparse that the cast is intentional.

    Fixes: 9a462b9 ("x86/percpu: Use compiler segment prefix qualifier")
    Reported-by: Charlemagne Lasse <charlemagnelasse@gmail.com>
    Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Link: https://lore.kernel.org/r/20240402175058.52649-1-ubizjak@gmail.com

    Closes: https://lore.kernel.org/lkml/CAFGhKbzev7W4aHwhFPWwMZQEHenVgZUj7=aunFieVqZg3mt14A@mail.gmail.com/

Signed-off-by: Waiman Long <longman@redhat.com>

Author: Waiman-Long

arch/x86/include/asm/percpu.h

@@ -77,7 +77,7 @@
 #define arch_raw_cpu_ptr(_ptr)					\
 ({								\
 	unsigned long tcp_ptr__ = __raw_my_cpu_offset;		\
-	tcp_ptr__ += (unsigned long)(_ptr);			\
+	tcp_ptr__ += (__force unsigned long)(_ptr);		\
 	(typeof(*(_ptr)) __kernel __force *)tcp_ptr__;		\
 })
 #else
@@ -96,8 +96,8 @@
 #endif /* CONFIG_SMP */
 
 #define __my_cpu_type(var)	typeof(var) __percpu_seg_override
-#define __my_cpu_ptr(ptr)	(__my_cpu_type(*ptr) *)(uintptr_t)(ptr)
-#define __my_cpu_var(var)	(*__my_cpu_ptr(&var))
+#define __my_cpu_ptr(ptr)	(__my_cpu_type(*ptr)*)(__force uintptr_t)(ptr)
+#define __my_cpu_var(var)	(*__my_cpu_ptr(&(var)))
 #define __percpu_arg(x)		__percpu_prefix "%" #x
 #define __force_percpu_arg(x)	__force_percpu_prefix "%" #x