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Date:   Mon, 19 Dec 2022 16:35:32 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     torvalds@linux-foundation.org
Cc:     corbet@lwn.net, will@kernel.org, peterz@infradead.org,
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Subject: [RFC][PATCH 07/12] percpu: Wire up cmpxchg128
References: <20221219153525.632521981@infradead.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Precedence: bulk

In order to replace cmpxchg_double() with the newly minted
cmpxchg128() family of functions, wire it up in this_cpu_cmpxchg().

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/arm64/include/asm/percpu.h |   24 ++++++++++++++++++
 arch/s390/include/asm/percpu.h  |   20 +++++++++++++++
 arch/x86/include/asm/percpu.h   |   52 ++++++++++++++++++++++++++++++++++++++++
 include/asm-generic/percpu.h    |    8 ++++++
 include/linux/percpu-defs.h     |   20 +++++++++++++--
 5 files changed, 122 insertions(+), 2 deletions(-)

--- a/arch/arm64/include/asm/percpu.h
+++ b/arch/arm64/include/asm/percpu.h
@@ -140,6 +140,10 @@ PERCPU_RET_OP(add, add, ldadd)
  * re-enabling preemption for preemptible kernels, but doing that in a way
  * which builds inside a module would mean messing directly with the preempt
  * count. If you do this, peterz and tglx will hunt you down.
+ *
+ * Not to mention it'll break the actual preemption model for missing a
+ * preemption point when TIF_NEED_RESCHED gets set while preemption is
+ * disabled.
  */
 #define this_cpu_cmpxchg_double_8(ptr1, ptr2, o1, o2, n1, n2)		\
 ({									\
@@ -240,6 +244,26 @@ PERCPU_RET_OP(add, add, ldadd)
 #define this_cpu_cmpxchg_8(pcp, o, n)	\
 	_pcp_protect_return(cmpxchg_relaxed, pcp, o, n)
 
+#define __pcpu_cast_128(_exp, _val)					\
+	_Generic((_exp),						\
+		 u128: (_val),						\
+		 s128: (_val),						\
+		 default: (unsigned long)(_val))
+
+#define this_cpu_cmpxchg_16(pcp, o, n)					\
+({									\
+	u128 old__ = __pcpu_cast_128((o), (o));				\
+	u128 new__ = __pcpu_cast_128((n), (n));				\
+	typedef typeof(pcp) pcp_op_T__;					\
+	pcp_op_T__ *ptr__;						\
+	u128 ret__;							\
+	preempt_disable_notrace();					\
+	ptr__ = raw_cpu_ptr(&(pcp));					\
+	ret__ = cmpxchg128_local((void *)ptr__, old__, new__);		\
+	preempt_enable_notrace();					\
+	(typeof(pcp))__pcpu_cast_128(*ptr__, ret__);			\
+})
+
 #ifdef __KVM_NVHE_HYPERVISOR__
 extern unsigned long __hyp_per_cpu_offset(unsigned int cpu);
 #define __per_cpu_offset
--- a/arch/s390/include/asm/percpu.h
+++ b/arch/s390/include/asm/percpu.h
@@ -148,6 +148,26 @@
 #define this_cpu_cmpxchg_4(pcp, oval, nval) arch_this_cpu_cmpxchg(pcp, oval, nval)
 #define this_cpu_cmpxchg_8(pcp, oval, nval) arch_this_cpu_cmpxchg(pcp, oval, nval)
 
+#define __pcpu_cast_128(_exp, _val)					\
+	_Generic((_exp),						\
+		 u128: (_val),						\
+		 s128: (_val),						\
+		 default: (unsigned long)(_val))
+
+#define this_cpu_cmpxchg_16(pcp, oval, nval)				\
+({									\
+	u128 old__ = __pcpu_cast_128((nval), (nval));			\
+	u128 new__ = __pcpu_cast_128((oval), (oval));			\
+	typedef typeof(pcp) pcp_op_T__;					\
+	pcp_op_T__ *ptr__;						\
+	u128 ret__;							\
+	preempt_disable_notrace();					\
+	ptr__ = raw_cpu_ptr(&(pcp));					\
+	ret__ = cmpxchg128((void *)ptr__, old__, new__);		\
+	preempt_enable_notrace();					\
+	(typeof(pcp))__pcpu_cast_128(*ptr__, ret__);			\
+})
+
 #define arch_this_cpu_xchg(pcp, nval)					\
 ({									\
 	typeof(pcp) *ptr__;						\
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -210,6 +210,58 @@ do {									\
 	(typeof(_var))(unsigned long) pco_old__;			\
 })
 
+#if defined(CONFIG_X86_32) && defined(CONFIG_X86_CMPXCHG64)
+#define __pcpu_cast_64(_exp, _val)					\
+	_Generic((_exp),						\
+		 u64: (_val),						\
+		 s64: (_val),						\
+		 default: (unsigned long)(_val))
+
+#define percpu_cmpxchg64_op(size, qual, _var, _oval, _nval)		\
+({									\
+	__pcpu_type_##size pco_old__ = __pcpu_cast_64((_oval), (_oval));\
+	__pcpu_type_##size pco_new__ = __pcpu_cast_64((_nval), (_nval));\
+	asm qual ("cmpxchg8b " __percpu_arg([var])			\
+		  : [var] "+m" (_var),					\
+		    "+A" (pco_old__)					\
+		  : "b" ((u32)pco_new__), "c" ((u32)(pco_new__ >> 32))	\
+		  : "memory");						\
+	(typeof(_var))__pcpu_cast_64(_var, pco_old__);			\
+})
+
+#define raw_cpu_cmpxchg_8(pcp, oval, nval)	percpu_cmpxchg64_op(8,         , pcp, oval, nval)
+#define this_cpu_cmpxchg_8(pcp, oval, nval)	percpu_cmpxchg64_op(8, volatile, pcp, oval, nval)
+#endif
+
+#ifdef CONFIG_X86_64
+#define __pcpu_cast_128(_exp, _val)					\
+	_Generic((_exp),						\
+		 u128: (_val),						\
+		 s128: (_val),						\
+		 default: (unsigned long)(_val))
+
+#define percpu_cmpxchg128_op(size, qual, _var, _oval, _nval)		\
+({									\
+	union __u128_halves pco_old__ = {				\
+		.full = __pcpu_cast_128((_oval), (_oval))		\
+	};								\
+	union __u128_halves pco_new__ = {				\
+		.full = __pcpu_cast_128((_nval), (_nval))		\
+	};								\
+	asm qual ("cmpxchg16b " __percpu_arg([var])			\
+		  : [var] "+m" (_var),					\
+		    "+a" (pco_old__.low),				\
+		    "+d" (pco_old__.high)				\
+		  : "b" (pco_new__.low),				\
+		    "c" (pco_new__.high)				\
+		  : "memory");						\
+	(typeof(_var))__pcpu_cast_128(_var, pco_old__.full);		\
+})
+
+#define raw_cpu_cmpxchg_16(pcp, oval, nval)	percpu_cmpxchg128_op(16,         , pcp, oval, nval)
+#define this_cpu_cmpxchg_16(pcp, oval, nval)	percpu_cmpxchg128_op(16, volatile, pcp, oval, nval)
+#endif
+
 /*
  * this_cpu_read() makes gcc load the percpu variable every time it is
  * accessed while this_cpu_read_stable() allows the value to be cached.
--- a/include/asm-generic/percpu.h
+++ b/include/asm-generic/percpu.h
@@ -298,6 +298,10 @@ do {									\
 #define raw_cpu_cmpxchg_8(pcp, oval, nval) \
 	raw_cpu_generic_cmpxchg(pcp, oval, nval)
 #endif
+#ifndef raw_cpu_cmpxchg_16
+#define raw_cpu_cmpxchg_16(pcp, oval, nval) \
+	raw_cpu_generic_cmpxchg(pcp, oval, nval)
+#endif
 
 #ifndef raw_cpu_cmpxchg_double_1
 #define raw_cpu_cmpxchg_double_1(pcp1, pcp2, oval1, oval2, nval1, nval2) \
@@ -423,6 +427,10 @@ do {									\
 #define this_cpu_cmpxchg_8(pcp, oval, nval) \
 	this_cpu_generic_cmpxchg(pcp, oval, nval)
 #endif
+#ifndef this_cpu_cmpxchg_16
+#define this_cpu_cmpxchg_16(pcp, oval, nval) \
+	this_cpu_generic_cmpxchg(pcp, oval, nval)
+#endif
 
 #ifndef this_cpu_cmpxchg_double_1
 #define this_cpu_cmpxchg_double_1(pcp1, pcp2, oval1, oval2, nval1, nval2) \
--- a/include/linux/percpu-defs.h
+++ b/include/linux/percpu-defs.h
@@ -343,6 +343,22 @@ static inline void __this_cpu_preempt_ch
 	pscr2_ret__;							\
 })
 
+#define __pcpu_size16_call_return2(stem, variable, ...)			\
+({									\
+	typeof(variable) pscr2_ret__;					\
+	__verify_pcpu_ptr(&(variable));					\
+	switch(sizeof(variable)) {					\
+	case 1: pscr2_ret__ = stem##1(variable, __VA_ARGS__); break;	\
+	case 2: pscr2_ret__ = stem##2(variable, __VA_ARGS__); break;	\
+	case 4: pscr2_ret__ = stem##4(variable, __VA_ARGS__); break;	\
+	case 8: pscr2_ret__ = stem##8(variable, __VA_ARGS__); break;	\
+	case 16: pscr2_ret__ = stem##16(variable, __VA_ARGS__); break;	\
+	default:							\
+		__bad_size_call_parameter(); break;			\
+	}								\
+	pscr2_ret__;							\
+})
+
 /*
  * Special handling for cmpxchg_double.  cmpxchg_double is passed two
  * percpu variables.  The first has to be aligned to a double word
@@ -425,7 +441,7 @@ do {									\
 #define raw_cpu_add_return(pcp, val)	__pcpu_size_call_return2(raw_cpu_add_return_, pcp, val)
 #define raw_cpu_xchg(pcp, nval)		__pcpu_size_call_return2(raw_cpu_xchg_, pcp, nval)
 #define raw_cpu_cmpxchg(pcp, oval, nval) \
-	__pcpu_size_call_return2(raw_cpu_cmpxchg_, pcp, oval, nval)
+	__pcpu_size16_call_return2(raw_cpu_cmpxchg_, pcp, oval, nval)
 #define raw_cpu_cmpxchg_double(pcp1, pcp2, oval1, oval2, nval1, nval2) \
 	__pcpu_double_call_return_bool(raw_cpu_cmpxchg_double_, pcp1, pcp2, oval1, oval2, nval1, nval2)
 
@@ -512,7 +528,7 @@ do {									\
 #define this_cpu_add_return(pcp, val)	__pcpu_size_call_return2(this_cpu_add_return_, pcp, val)
 #define this_cpu_xchg(pcp, nval)	__pcpu_size_call_return2(this_cpu_xchg_, pcp, nval)
 #define this_cpu_cmpxchg(pcp, oval, nval) \
-	__pcpu_size_call_return2(this_cpu_cmpxchg_, pcp, oval, nval)
+	__pcpu_size16_call_return2(this_cpu_cmpxchg_, pcp, oval, nval)
 #define this_cpu_cmpxchg_double(pcp1, pcp2, oval1, oval2, nval1, nval2) \
 	__pcpu_double_call_return_bool(this_cpu_cmpxchg_double_, pcp1, pcp2, oval1, oval2, nval1, nval2)