2024-03-19 17:17:35

by Uros Bizjak

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 <[email protected]>
Cc: Yu-cheng Yu <[email protected]>
Cc: Rick Edgecombe <[email protected]>
Cc: Borislav Petkov (AMD) <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Mike Rapoport (IBM) <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: H. Peter Anvin <[email protected]>
---
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 0ee2ba589492..aec6e2d3aa1d 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:
--
2.42.0

2024-03-20 11:22:31

by tip-bot2 for Jacob Pan

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 <[email protected]>
AuthorDate: Tue, 19 Mar 2024 18:16:46 +01:00
Committer: Ingo Molnar <[email protected]>
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 <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
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: