linux-kernel - [PATCH v7 RESEND 5/6] arm64: futex: small optimisation for __llsc_futex_atomic

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20250816151929.197589-6-yeoreum.yun@arm.com>
Date: Sat, 16 Aug 2025 16:19:28 +0100
From: Yeoreum Yun <yeoreum.yun@....com>
To: catalin.marinas@....com,
	will@...nel.org,
	broonie@...nel.org,
	maz@...nel.org,
	oliver.upton@...ux.dev,
	joey.gouly@....com,
	james.morse@....com,
	ardb@...nel.org,
	scott@...amperecomputing.com,
	suzuki.poulose@....com,
	yuzenghui@...wei.com,
	mark.rutland@....com
Cc: linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Yeoreum Yun <yeoreum.yun@....com>
Subject: [PATCH v7 RESEND 5/6] arm64: futex: small optimisation for __llsc_futex_atomic_set()

__llsc_futex_atomic_set() is implmented using
LLSC_FUTEX_ATOMIC_OP() macro with "mov  %w3, %w5".
But this instruction isn't required to implement fux_atomic_set()
so make a small optimisation by implementing __llsc_futex_atomic_set()
as separate function.

This will make usage of LLSC_FUTEX_ATOMIC_OP() macro more simple.

Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>
---
 arch/arm64/include/asm/futex.h | 43 ++++++++++++++++++++++++++++------
 1 file changed, 36 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h
index ab7003cb4724..22a6301a9f3d 100644
--- a/arch/arm64/include/asm/futex.h
+++ b/arch/arm64/include/asm/futex.h
@@ -13,7 +13,7 @@

 #define LLSC_MAX_LOOPS	128 /* What's the largest number you can think of? */

-#define LLSC_FUTEX_ATOMIC_OP(op, insn)					\
+#define LLSC_FUTEX_ATOMIC_OP(op, asm_op)				\
 static __always_inline int						\
 __llsc_futex_atomic_##op(int oparg, u32 __user *uaddr, int *oval)	\
 {									\
@@ -24,7 +24,7 @@ __llsc_futex_atomic_##op(int oparg, u32 __user *uaddr, int *oval)	\
 	asm volatile("// __llsc_futex_atomic_" #op "\n"			\
 "	prfm	pstl1strm, %2\n"					\
 "1:	ldxr	%w1, %2\n"						\
-	insn "\n"							\
+"	" #asm_op "	%w3, %w1, %w5\n"				\
 "2:	stlxr	%w0, %w3, %2\n"						\
 "	cbz	%w0, 3f\n"						\
 "	sub	%w4, %w4, %w0\n"					\
@@ -46,11 +46,40 @@ __llsc_futex_atomic_##op(int oparg, u32 __user *uaddr, int *oval)	\
 	return ret;							\
 }

-LLSC_FUTEX_ATOMIC_OP(add, "add	%w3, %w1, %w5")
-LLSC_FUTEX_ATOMIC_OP(or, "orr	%w3, %w1, %w5")
-LLSC_FUTEX_ATOMIC_OP(and, "and	%w3, %w1, %w5")
-LLSC_FUTEX_ATOMIC_OP(eor, "eor	%w3, %w1, %w5")
-LLSC_FUTEX_ATOMIC_OP(set, "mov	%w3, %w5")
+LLSC_FUTEX_ATOMIC_OP(add, add)
+LLSC_FUTEX_ATOMIC_OP(or, orr)
+LLSC_FUTEX_ATOMIC_OP(and, and)
+LLSC_FUTEX_ATOMIC_OP(eor, eor)
+
+static __always_inline int
+__llsc_futex_atomic_set(int oparg, u32 __user *uaddr, int *oval)
+{
+	unsigned int loops = LLSC_MAX_LOOPS;
+	int ret, oldval;
+
+	uaccess_enable_privileged();
+	asm volatile("//__llsc_futex_xchg\n"
+"	prfm	pstl1strm, %2\n"
+"1:	ldxr	%w1, %2\n"
+"2:	stlxr	%w0, %w4, %2\n"
+"	cbz	%w3, 3f\n"
+"	sub	%w3, %w3, %w0\n"
+"	cbnz	%w3, 1b\n"
+"	mov	%w0, %w5\n"
+"3:\n"
+"	dmb	ish\n"
+	_ASM_EXTABLE_UACCESS_ERR(1b, 3b, %w0)
+	_ASM_EXTABLE_UACCESS_ERR(2b, 3b, %w0)
+	: "=&r" (ret), "=&r" (oldval), "+Q" (*uaddr), "+r" (loops)
+	: "r" (oparg), "Ir" (-EAGAIN)
+	: "memory");
+	uaccess_disable_privileged();
+
+	if (!ret)
+		*oval = oldval;
+
+	return ret;
+}

 static __always_inline int
 __llsc_futex_cmpxchg(u32 __user *uaddr, u32 oldval, u32 newval, u32 *oval)
--
LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}