[PATCH cmpxchg 14/14] riscv: Emulate one-byte cmpxchg

Paul E. McKenney
2024-04-08T17:49:47Z

Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on riscv.

[ paulmck: Apply kernel test robot feedback. ]
[ paulmck: Drop two-byte support per Arnd Bergmann feedback. ]

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Yujie Liu <yujie.liu@intel.com>
Cc: Andi Shyti <andi.shyti@linux.intel.com>
Cc: Andrzej Hajda <andrzej.hajda@intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: <linux-riscv@lists.infradead.org>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
---
arch/riscv/Kconfig | 1 +
arch/riscv/include/asm/cmpxchg.h | 13 +++++++++++++
2 files changed, 14 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index be09c8836d56b..3bab9c5c0f465 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -44,6 +44,7 @@ config RISCV
select ARCH_HAS_UBSAN
select ARCH_HAS_VDSO_DATA
select ARCH_KEEP_MEMBLOCK if ACPI
+ select ARCH_NEED_CMPXCHG_1_EMU
select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
select ARCH_STACKWALK
diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h
index 2fee65cc84432..abcd5543b861b 100644
--- a/arch/riscv/include/asm/cmpxchg.h
+++ b/arch/riscv/include/asm/cmpxchg.h
@@ -9,6 +9,7 @@
#include <linux/bug.h>

#include <asm/fence.h>
+#include <linux/cmpxchg-emu.h>

#define __xchg_relaxed(ptr, new, size) \
({ \
@@ -170,6 +171,9 @@
__typeof__(*(ptr)) __ret; \
register unsigned int __rc; \
switch (size) { \
+ case 1: \
+ __ret = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *)__ptr, (uintptr_t)__old, (uintptr_t)__new); \
+ break; \
case 4: \
__asm__ __volatile__ ( \
"0: lr.w %0, %2\n" \
@@ -214,6 +218,9 @@
__typeof__(*(ptr)) __ret; \
register unsigned int __rc; \
switch (size) { \
+ case 1: \
+ __ret = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *)__ptr, __old, __new); \
+ break; \
case 4: \
__asm__ __volatile__ ( \
"0: lr.w %0, %2\n" \
@@ -260,6 +267,9 @@
__typeof__(*(ptr)) __ret; \
register unsigned int __rc; \
switch (size) { \
+ case 1: \
+ __ret = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *)__ptr, __old, __new); \
+ break; \
case 4: \
__asm__ __volatile__ ( \
RISCV_RELEASE_BARRIER \
@@ -306,6 +316,9 @@
__typeof__(*(ptr)) __ret; \
register unsigned int __rc; \
switch (size) { \
+ case 1: \
+ __ret = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *)__ptr, __old, __new); \
+ break; \
case 4: \
__asm__ __volatile__ ( \
"0: lr.w %0, %2\n" \
--
2.40.1