From 648337147d3550c1ca3d1b500e66dbda12e2d836 Mon Sep 17 00:00:00 2001 From: Uros Bizjak Date: Tue, 19 Mar 2024 18:16:46 +0100 Subject: [PATCH] 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 Signed-off-by: Ingo Molnar Cc: Linus Torvalds Cc: Josh Poimboeuf Cc: Ard Biesheuvel Cc: "H. Peter Anvin" 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 0ee2ba589492b..aec6e2d3aa1d5 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: -- 2.30.2