[tip: x86/asm] x86/runtime-const: Add the RUNTIME_CONST_PTR assembly macro

[tip-bot2 for Kirill A. Shutemov]

The following commit has been merged into the x86/asm branch of tip:

Commit-ID:     c84f87de474c9aec84f706ceb732b70751122746
Gitweb:        https://git.kernel.org/tip/c84f87de474c9aec84f706ceb732b70751122746
Author:        Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
AuthorDate:    Tue, 04 Mar 2025 17:33:42 +02:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Thu, 06 Mar 2025 11:27:31 +01:00

x86/runtime-const: Add the RUNTIME_CONST_PTR assembly macro

Add an assembly macro to refer runtime cost. It hides linker magic and
makes assembly more readable.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20250304153342.2016569-1-kirill.shutemov@xxxxxxxxxxxxxxx
---
 arch/x86/include/asm/runtime-const.h | 13 +++++++++++++
 arch/x86/lib/getuser.S               |  7 ++-----
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/runtime-const.h b/arch/x86/include/asm/runtime-const.h
index 6652ebd..8d983cf 100644
--- a/arch/x86/include/asm/runtime-const.h
+++ b/arch/x86/include/asm/runtime-const.h
@@ -2,6 +2,18 @@
 #ifndef _ASM_RUNTIME_CONST_H
 #define _ASM_RUNTIME_CONST_H
 
+#ifdef __ASSEMBLY__
+
+.macro RUNTIME_CONST_PTR sym reg
+	movq	$0x0123456789abcdef, %\reg
+	1:
+	.pushsection runtime_ptr_\sym, "a"
+	.long	1b - 8 - .
+	.popsection
+.endm
+
+#else /* __ASSEMBLY__ */
+
 #define runtime_const_ptr(sym) ({				\
 	typeof(sym) __ret;					\
 	asm_inline("mov %1,%0\n1:\n"				\
@@ -58,4 +70,5 @@ static inline void runtime_const_fixup(void (*fn)(void *, unsigned long),
 	}
 }
 
+#endif /* __ASSEMBLY__ */
 #endif
diff --git a/arch/x86/lib/getuser.S b/arch/x86/lib/getuser.S
index 89ecd57..853a2e6 100644
--- a/arch/x86/lib/getuser.S
+++ b/arch/x86/lib/getuser.S
@@ -34,16 +34,13 @@
 #include <asm/thread_info.h>
 #include <asm/asm.h>
 #include <asm/smap.h>
+#include <asm/runtime-const.h>
 
 #define ASM_BARRIER_NOSPEC ALTERNATIVE "", "lfence", X86_FEATURE_LFENCE_RDTSC
 
 .macro check_range size:req
 .if IS_ENABLED(CONFIG_X86_64)
-	movq $0x0123456789abcdef,%rdx
-  1:
-  .pushsection runtime_ptr_USER_PTR_MAX,"a"
-	.long 1b - 8 - .
-  .popsection
+	RUNTIME_CONST_PTR USER_PTR_MAX, rdx
 	cmp %rdx, %rax
 	cmova %rdx, %rax
 .else