linux-kernel - [tip: x86/asm] x86/asm: Use "m" operand constraint in WRUSSQ asm template

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Date: Wed, 20 Mar 2024 11:21:40 -0000
From: "tip-bot2 for Uros Bizjak" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Uros Bizjak <ubizjak@...il.com>, Ingo Molnar <mingo@...nel.org>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 Josh Poimboeuf <jpoimboe@...hat.com>, Ard Biesheuvel <ardb@...nel.org>,
 "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject:
 [tip: x86/asm] x86/asm: Use "m" operand constraint in WRUSSQ asm template

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

Commit-ID:     648337147d3550c1ca3d1b500e66dbda12e2d836
Gitweb:        https://git.kernel.org/tip/648337147d3550c1ca3d1b500e66dbda12e2d836
Author:        Uros Bizjak <ubizjak@...il.com>
AuthorDate:    Tue, 19 Mar 2024 18:16:46 +01:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Wed, 20 Mar 2024 12:04:38 +01:00

x86/asm: Use "m" operand constraint in WRUSSQ asm template

The WRUSSQ instruction uses a memory operand, so use "m"
operand constraint instead of forcing usage of pointer
register using "r" constraint. The generated assembly
code improves from:

   6ece3:	48 8d 43 f8          	lea    -0x8(%rbx),%rax
   ...
   6eceb:	66 48 0f 38 f5 18    	wrussq %rbx,(%rax)

to:

   6ecea:	66 48 0f 38 f5 43 f8 	wrussq %rax,-0x8(%rbx)

Signed-off-by: Uros Bizjak <ubizjak@...il.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Ard Biesheuvel <ardb@...nel.org>
Cc: "H. Peter Anvin" <hpa@...or.com>
Link: https://lore.kernel.org/r/20240319171714.76342-1-ubizjak@gmail.com
---
 arch/x86/include/asm/special_insns.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h
index 0ee2ba5..aec6e2d 100644
--- a/arch/x86/include/asm/special_insns.h
+++ b/arch/x86/include/asm/special_insns.h
@@ -205,9 +205,9 @@ static inline void clwb(volatile void *__p)
 #ifdef CONFIG_X86_USER_SHADOW_STACK
 static inline int write_user_shstk_64(u64 __user *addr, u64 val)
 {
-	asm goto("1: wrussq %[val], (%[addr])\n"
+	asm goto("1: wrussq %[val], %[addr]\n"
 			  _ASM_EXTABLE(1b, %l[fail])
-			  :: [addr] "r" (addr), [val] "r" (val)
+			  :: [addr] "m" (*addr), [val] "r" (val)
 			  :: fail);
 	return 0;
 fail: