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Peter Anvin" Subject: [PATCH] x86/asm: Use "m" operand constraint in WRUSSQ asm template Date: Tue, 19 Mar 2024 18:16:46 +0100 Message-ID: <20240319171714.76342-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.42.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 Cc: Yu-cheng Yu Cc: Rick Edgecombe Cc: Borislav Petkov (AMD) Cc: Kees Cook Cc: Mike Rapoport (IBM) Cc: Ingo Molnar Cc: Dave Hansen Cc: Andy Lutomirski Cc: H. Peter Anvin --- 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/sp= ecial_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: --=20 2.42.0