linux-kernel - [PATCH 07/12] percpu: #ifndef __SIZEOF_INT128_

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Date:   Wed, 31 May 2023 15:08:40 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     torvalds@...ux-foundation.org
Cc:     corbet@....net, will@...nel.org, peterz@...radead.org,
        boqun.feng@...il.com, mark.rutland@....com,
        catalin.marinas@....com, dennis@...nel.org, tj@...nel.org,
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Subject: [PATCH 07/12] percpu: #ifndef __SIZEOF_INT128__

Some 64bit architectures do not advertise __SIZEOF_INT128__ on all
supported compiler versions. Notably the HPPA64 only started doing
with GCC-11.

Since the per-cpu ops are universally availably, and
this_cpu_{,try_}cmpxchg128() is expected to be available on all 64bit
architectures a wee bodge is in order.

Sadly, while C reverts to memcpy() for assignment of POD types, it does
not revert to memcmp() for for equality. Therefore frob that manually.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 include/asm-generic/percpu.h |   56 +++++++++++++++++++++++++++++++++++++++++++
 include/linux/types.h        |    7 +++++
 2 files changed, 63 insertions(+)

--- a/include/asm-generic/percpu.h
+++ b/include/asm-generic/percpu.h
@@ -313,6 +313,35 @@ do {									\
 #define raw_cpu_xchg_8(pcp, nval)	raw_cpu_generic_xchg(pcp, nval)
 #endif
 
+#ifndef __SIZEOF_INT128__
+#define raw_cpu_generic_try_cmpxchg_memcmp(pcp, ovalp, nval)		\
+({									\
+	typeof(pcp) *__p = raw_cpu_ptr(&(pcp));				\
+	typeof(pcp) __val = *__p, __old = *(ovalp);			\
+	bool __ret;							\
+	if (!__builtin_memcmp(&__val, &__old, sizeof(pcp))) {		\
+		*__p = nval;						\
+		__ret = true;						\
+	} else {							\
+		*(ovalp) = __val;					\
+		__ret = false;						\
+	}								\
+	__ret;								\
+})
+
+#define raw_cpu_generic_cmpxchg_memcmp(pcp, oval, nval)			\
+({									\
+	typeof(pcp) __old = (oval);					\
+	raw_cpu_generic_try_cmpxchg_memcpy(pcp, &__old, nval);		\
+	__old;								\
+})
+
+#define raw_cpu_cmpxchg128(pcp, oval, nval) \
+	raw_cpu_generic_cmpxchg_memcmp(pcp, oval, nval)
+#define raw_cpu_try_cmpxchg128(pcp, ovalp, nval) \
+	raw_cpu_generic_try_cmpxchg_memcmp(pcp, ovalp, nval)
+#endif
+
 #ifndef raw_cpu_try_cmpxchg_1
 #ifdef raw_cpu_cmpxchg_1
 #define raw_cpu_try_cmpxchg_1(pcp, ovalp, nval) \
@@ -503,6 +532,33 @@ do {									\
 #define this_cpu_xchg_8(pcp, nval)	this_cpu_generic_xchg(pcp, nval)
 #endif
 
+#ifndef __SIZEOF_INT128__
+#define this_cpu_generic_try_cmpxchg_memcmp(pcp, ovalp, nval)		\
+({									\
+	bool __ret;							\
+	unsigned long __flags;						\
+	raw_local_irq_save(__flags);					\
+	__ret = raw_cpu_generic_try_cmpxchg_memcmp(pcp, ovalp, nval);	\
+	raw_local_irq_restore(__flags);					\
+	__ret;								\
+})
+
+#define this_cpu_generic_cmpxchg_memcmp(pcp, oval, nval)		\
+({									\
+	typeof(pcp) __ret;						\
+	unsigned long __flags;						\
+	raw_local_irq_save(__flags);					\
+	__ret = raw_cpu_generic_cmpxchg_memcmp(pcp, oval, nval);	\
+	raw_local_irq_restore(__flags);					\
+	__ret;								\
+})
+
+#define this_cpu_cmpxchg128(pcp, oval, nval) \
+	this_cpu_generic_cmpxchg_memcmp(pcp, oval, nval)
+#define this_cpu_try_cmpxchg128(pcp, ovalp, nval) \
+	this_cpu_generic_try_cmpxchg_memcmp(pcp, ovalp, nval)
+#endif
+
 #ifndef this_cpu_try_cmpxchg_1
 #ifdef this_cpu_cmpxchg_1
 #define this_cpu_try_cmpxchg_1(pcp, ovalp, nval) \
--- a/include/linux/types.h
+++ b/include/linux/types.h
@@ -13,6 +13,13 @@
 #ifdef __SIZEOF_INT128__
 typedef __s128 s128;
 typedef __u128 u128;
+#else
+#ifdef CONFIG_64BIT
+/* hack for this_cpu_cmpxchg128 */
+typedef struct {
+	u64 a, b;
+} u128 __attribute__((aligned(16)));
+#endif
 #endif
 
 typedef u32 __kernel_dev_t;