[RFC PATCH 17/22] riscv: s64ilp32: Implement cmpxchg_double

[guoren]

From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>

The s64ilp32 has the ability to exclusively load and store (ld/sd)
a pair of words from an address. Then the SLUB can take advantage
of a cmpxchg_double implementation to avoid taking some locks.

This patch provides an implementation of cmpxchg_double for 64-bit
pairs, and activates the logic required for the SLUB to use these
functions (HAVE_ALIGNED_STRUCT_PAGE and HAVE_CMPXCHG_DOUBLE).

Similar commit: 5284e1b4bc8a ("arm64: xchg: Implement
cmpxchg_double")

Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
---
 arch/riscv/Kconfig               |  2 ++
 arch/riscv/include/asm/cmpxchg.h | 53 ++++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index e0c3dee68510..51853f883fc5 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -78,6 +78,7 @@ config RISCV
 	select GENERIC_TIME_VSYSCALL if MMU
 	select GENERIC_VDSO_TIME_NS if HAVE_GENERIC_VDSO
 	select HARDIRQS_SW_RESEND
+	select HAVE_ALIGNED_STRUCT_PAGE if SLUB && ARCH_RV64ILP32
 	select HAVE_ARCH_AUDITSYSCALL
 	select HAVE_ARCH_HUGE_VMALLOC if HAVE_ARCH_HUGE_VMAP
 	select HAVE_ARCH_HUGE_VMAP if MMU && 64BIT && !XIP_KERNEL
@@ -96,6 +97,7 @@ config RISCV
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if 64BIT && MMU
 	select HAVE_ARCH_VMAP_STACK if MMU && 64BIT
 	select HAVE_ASM_MODVERSIONS
+	select HAVE_CMPXCHG_DOUBLE if ARCH_RV64ILP32
 	select HAVE_CONTEXT_TRACKING_USER
 	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_DMA_CONTIGUOUS if MMU
diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h
index 12debce235e5..808730d151e7 100644
--- a/arch/riscv/include/asm/cmpxchg.h
+++ b/arch/riscv/include/asm/cmpxchg.h
@@ -7,6 +7,7 @@
 #define _ASM_RISCV_CMPXCHG_H
 
 #include <linux/bug.h>
+#include <linux/mmdebug.h>
 
 #include <asm/barrier.h>
 #include <asm/fence.h>
@@ -360,4 +361,56 @@
 	arch_cmpxchg_relaxed((ptr), (o), (n));				\
 })
 
+#ifdef CONFIG_ARCH_RV64ILP32
+#define system_has_cmpxchg_double()	1
+
+#define __cmpxchg_double_check(ptr1, ptr2)				\
+({									\
+	if (sizeof(*(ptr1)) != 4)					\
+		BUILD_BUG();						\
+	if (sizeof(*(ptr2)) != 4)					\
+		BUILD_BUG();						\
+	VM_BUG_ON((ulong *)(ptr2) - (ulong *)(ptr1) != 1);		\
+	VM_BUG_ON(((ulong)ptr1 & 0x7) != 0);				\
+})
+
+#define __cmpxchg_double(old1, old2, new1, new2, ptr)			\
+({									\
+	__typeof__(ptr) __ptr = (ptr);					\
+	register unsigned int __ret;					\
+	u64 __old;							\
+	u64 __new;							\
+	u64 __tmp;							\
+	switch (sizeof(*(ptr))) {					\
+	case 4:								\
+		__old = ((u64)old2 << 32) | (u64)old1;			\
+		__new = ((u64)new2 << 32) | (u64)new1;			\
+		__asm__ __volatile__ (					\
+			"0:	lr.d %0, %2\n"				\
+			"	bne %0, %z3, 1f\n"			\
+			"	sc.d %1, %z4, %2\n"			\
+			"	bnez %1, 0b\n"				\
+			"1:\n"						\
+			: "=&r" (__tmp), "=&r" (__ret), "+A" (*__ptr)	\
+			: "rJ" (__old), "rJ" (__new)			\
+			: "memory");					\
+		__ret = (__old == __tmp);				\
+		break;							\
+	default:							\
+		BUILD_BUG();						\
+	}								\
+	__ret;								\
+})
+
+#define arch_cmpxchg_double(ptr1, ptr2, o1, o2, n1, n2)			\
+({									\
+	int __ret;							\
+	__cmpxchg_double_check(ptr1, ptr2);				\
+	__ret = __cmpxchg_double((ulong)(o1), (ulong)(o2),		\
+				 (ulong)(n1), (ulong)(n2),		\
+				  ptr1);				\
+	__ret;								\
+})
+#endif
+
 #endif /* _ASM_RISCV_CMPXCHG_H */
-- 
2.36.1