linux-kernel - [RFC PATCH 4/4] riscv: Use Zalasr for smp_load_acquire/smp_store

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Message-Id: <20250826145740.92276-5-luxu.kernel@bytedance.com>
Date: Tue, 26 Aug 2025 22:57:40 +0800
From: Xu Lu <luxu.kernel@...edance.com>
To: paul.walmsley@...ive.com,
	palmer@...belt.com,
	aou@...s.berkeley.edu,
	alex@...ti.fr,
	ajones@...tanamicro.com,
	brs@...osinc.com
Cc: linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Xu Lu <luxu.kernel@...edance.com>
Subject: [RFC PATCH 4/4] riscv: Use Zalasr for smp_load_acquire/smp_store_release

Replace fence instructions with Zalasr instructions during acquire or
release operations.

Signed-off-by: Xu Lu <luxu.kernel@...edance.com>
---
 arch/riscv/include/asm/barrier.h | 79 +++++++++++++++++++++++++++-----
 1 file changed, 68 insertions(+), 11 deletions(-)

diff --git a/arch/riscv/include/asm/barrier.h b/arch/riscv/include/asm/barrier.h
index b8c5726d86acb..b1d2a9a85256d 100644
--- a/arch/riscv/include/asm/barrier.h
+++ b/arch/riscv/include/asm/barrier.h
@@ -51,19 +51,76 @@
  */
 #define smp_mb__after_spinlock()	RISCV_FENCE(iorw, iorw)
 
-#define __smp_store_release(p, v)					\
-do {									\
-	compiletime_assert_atomic_type(*p);				\
-	RISCV_FENCE(rw, w);						\
-	WRITE_ONCE(*p, v);						\
+extern void __bad_size_call_parameter(void);
+
+#define __smp_store_release(p, v)						\
+do {										\
+	compiletime_assert_atomic_type(*p);					\
+	switch (sizeof(*p)) {							\
+	case 1:									\
+		asm volatile(ALTERNATIVE("fence rw, w;\t\nsb %0, 0(%1)\t\n",	\
+					 SB_RL(%0, %1) "\t\nnop\t\n",		\
+					 0, RISCV_ISA_EXT_ZALASR, 1)		\
+					 : : "r" (v), "r" (p) : "memory");	\
+		break;								\
+	case 2:									\
+		asm volatile(ALTERNATIVE("fence rw, w;\t\nsh %0, 0(%1)\t\n",	\
+					 SH_RL(%0, %1) "\t\nnop\t\n",		\
+					 0, RISCV_ISA_EXT_ZALASR, 1)		\
+					 : : "r" (v), "r" (p) : "memory");	\
+		break;								\
+	case 4:									\
+		asm volatile(ALTERNATIVE("fence rw, w;\t\nsw %0, 0(%1)\t\n",	\
+					 SW_RL(%0, %1) "\t\nnop\t\n",		\
+					 0, RISCV_ISA_EXT_ZALASR, 1)		\
+					 : : "r" (v), "r" (p) : "memory");	\
+		break;								\
+	case 8:									\
+		asm volatile(ALTERNATIVE("fence rw, w;\t\nsd %0, 0(%1)\t\n",	\
+					 SD_RL(%0, %1) "\t\nnop\t\n",		\
+					 0, RISCV_ISA_EXT_ZALASR, 1)		\
+					 : : "r" (v), "r" (p) : "memory");	\
+		break;								\
+	default:								\
+		__bad_size_call_parameter();					\
+		break;								\
+	}									\
 } while (0)
 
-#define __smp_load_acquire(p)						\
-({									\
-	typeof(*p) ___p1 = READ_ONCE(*p);				\
-	compiletime_assert_atomic_type(*p);				\
-	RISCV_FENCE(r, rw);						\
-	___p1;								\
+#define __smp_load_acquire(p)							\
+({										\
+	TYPEOF_UNQUAL(*p) val;							\
+	compiletime_assert_atomic_type(*p);					\
+	switch (sizeof(*p)) {							\
+	case 1:									\
+		asm volatile(ALTERNATIVE("lb %0, 0(%1)\t\nfence r, rw\t\n",	\
+					 LB_AQ(%0, %1) "\t\nnop\t\n",		\
+					 0, RISCV_ISA_EXT_ZALASR, 1)		\
+					 : "=r" (val) : "r" (p) : "memory");	\
+		break;								\
+	case 2:									\
+		asm volatile(ALTERNATIVE("lh %0, 0(%1)\t\nfence r, rw\t\n",	\
+					 LH_AQ(%0, %1) "\t\nnop\t\n",		\
+					 0, RISCV_ISA_EXT_ZALASR, 1)		\
+					 : "=r" (val) : "r" (p) : "memory");	\
+		break;								\
+	case 4:									\
+		asm volatile(ALTERNATIVE("lw %0, 0(%1)\t\nfence r, rw\t\n",	\
+					 LW_AQ(%0, %1) "\t\nnop\t\n",		\
+					 0, RISCV_ISA_EXT_ZALASR, 1)		\
+					 : "=r" (val) : "r" (p) : "memory");	\
+		break;								\
+	case 8:									\
+		asm volatile(ALTERNATIVE("ld %0, 0(%1)\t\nfence r, rw\t\n",	\
+					 LD_AQ(%0, %1) "\t\nnop\t\n",		\
+					 0, RISCV_ISA_EXT_ZALASR, 1)		\
+					 : "=r" (val) : "r" (p) : "memory");	\
+		break;								\
+	default:								\
+		__bad_size_call_parameter();					\
+		break;								\
+	}									\
+	val;									\
 })
 
 #ifdef CONFIG_RISCV_ISA_ZAWRS
-- 
2.20.1