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Commit 959bf2fd authored by Will Deacon's avatar Will Deacon
Browse files

arm64: percpu: Rewrite per-cpu ops to allow use of LSE atomics 



Our percpu code is a bit of an inconsistent mess:

  * It rolls its own xchg(), but reuses cmpxchg_local()
  * It uses various different flavours of preempt_{enable,disable}()
  * It returns values even for the non-returning RmW operations
  * It makes no use of LSE atomics outside of the cmpxchg() ops
  * There are individual macros for different sizes of access, but these
    are all funneled through a switch statement rather than dispatched
    directly to the relevant case

This patch rewrites the per-cpu operations to address these shortcomings.
Whilst the new code is a lot cleaner, the big advantage is that we can
use the non-returning ST- atomic instructions when we have LSE.

Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent b4f9209b

arch/arm64/include/asm/percpu.h

+160 −230
Original line number Diff line number Diff line
@@ -48,263 +48,193 @@ static inline unsigned long __my_cpu_offset(void) 
}

#define __my_cpu_offset __my_cpu_offset()



#define PERCPU_OP(op, asm_op)						\

static inline unsigned long __percpu_##op(void *ptr,			\

			unsigned long val, int size)			\

#define PERCPU_RW_OPS(sz)						\

static inline unsigned long __percpu_read_##sz(void *ptr)		\

{									\

	unsigned long loop, ret;					\

									\

	switch (size) {							\

	case 1:								\

		asm ("//__per_cpu_" #op "_1\n"				\

		"1:	ldxrb	  %w[ret], %[ptr]\n"			\

			#asm_op " %w[ret], %w[ret], %w[val]\n"		\

		"	stxrb	  %w[loop], %w[ret], %[ptr]\n"		\

		"	cbnz	  %w[loop], 1b"				\

		: [loop] "=&r" (loop), [ret] "=&r" (ret),		\

		  [ptr] "+Q"(*(u8 *)ptr)				\

		: [val] "Ir" (val));					\

		break;							\

	case 2:								\

		asm ("//__per_cpu_" #op "_2\n"				\

		"1:	ldxrh	  %w[ret], %[ptr]\n"			\

			#asm_op " %w[ret], %w[ret], %w[val]\n"		\

		"	stxrh	  %w[loop], %w[ret], %[ptr]\n"		\

		"	cbnz	  %w[loop], 1b"				\

		: [loop] "=&r" (loop), [ret] "=&r" (ret),		\

		  [ptr]  "+Q"(*(u16 *)ptr)				\

		: [val] "Ir" (val));					\

		break;							\

	case 4:								\

		asm ("//__per_cpu_" #op "_4\n"				\

		"1:	ldxr	  %w[ret], %[ptr]\n"			\

			#asm_op " %w[ret], %w[ret], %w[val]\n"		\

		"	stxr	  %w[loop], %w[ret], %[ptr]\n"		\

		"	cbnz	  %w[loop], 1b"				\

		: [loop] "=&r" (loop), [ret] "=&r" (ret),		\

		  [ptr] "+Q"(*(u32 *)ptr)				\

		: [val] "Ir" (val));					\

		break;							\

	case 8:								\

		asm ("//__per_cpu_" #op "_8\n"				\

		"1:	ldxr	  %[ret], %[ptr]\n"			\

			#asm_op " %[ret], %[ret], %[val]\n"		\

		"	stxr	  %w[loop], %[ret], %[ptr]\n"		\

		"	cbnz	  %w[loop], 1b"				\

		: [loop] "=&r" (loop), [ret] "=&r" (ret),		\

		  [ptr] "+Q"(*(u64 *)ptr)				\

		: [val] "Ir" (val));					\

		break;							\

	default:							\

		ret = 0;						\

		BUILD_BUG();						\

	return READ_ONCE(*(u##sz *)ptr);				\

}									\

									\

	return ret;							\

}



PERCPU_OP(add, add)

PERCPU_OP(and, and)

PERCPU_OP(or, orr)

#undef PERCPU_OP



static inline unsigned long __percpu_read(void *ptr, int size)

{

	unsigned long ret;



	switch (size) {

	case 1:

		ret = READ_ONCE(*(u8 *)ptr);

		break;

	case 2:

		ret = READ_ONCE(*(u16 *)ptr);

		break;

	case 4:

		ret = READ_ONCE(*(u32 *)ptr);

		break;

	case 8:

		ret = READ_ONCE(*(u64 *)ptr);

		break;

	default:

		ret = 0;

		BUILD_BUG();

	}



	return ret;

}



static inline void __percpu_write(void *ptr, unsigned long val, int size)

{

	switch (size) {

	case 1:

		WRITE_ONCE(*(u8 *)ptr, (u8)val);

		break;

	case 2:

		WRITE_ONCE(*(u16 *)ptr, (u16)val);

		break;

	case 4:

		WRITE_ONCE(*(u32 *)ptr, (u32)val);

		break;

	case 8:

		WRITE_ONCE(*(u64 *)ptr, (u64)val);

		break;

	default:

		BUILD_BUG();

	}

static inline void __percpu_write_##sz(void *ptr, unsigned long val)	\

{									\

	WRITE_ONCE(*(u##sz *)ptr, (u##sz)val);				\

}



static inline unsigned long __percpu_xchg(void *ptr, unsigned long val,

						int size)

{

	unsigned long ret, loop;



	switch (size) {

	case 1:

		asm ("//__percpu_xchg_1\n"

		"1:	ldxrb	%w[ret], %[ptr]\n"

		"	stxrb	%w[loop], %w[val], %[ptr]\n"

		"	cbnz	%w[loop], 1b"

		: [loop] "=&r"(loop), [ret] "=&r"(ret),

		  [ptr] "+Q"(*(u8 *)ptr)

		: [val] "r" (val));

		break;

	case 2:

		asm ("//__percpu_xchg_2\n"

		"1:	ldxrh	%w[ret], %[ptr]\n"

		"	stxrh	%w[loop], %w[val], %[ptr]\n"

		"	cbnz	%w[loop], 1b"

		: [loop] "=&r"(loop), [ret] "=&r"(ret),

		  [ptr] "+Q"(*(u16 *)ptr)

		: [val] "r" (val));

		break;

	case 4:

		asm ("//__percpu_xchg_4\n"

		"1:	ldxr	%w[ret], %[ptr]\n"

		"	stxr	%w[loop], %w[val], %[ptr]\n"

		"	cbnz	%w[loop], 1b"

		: [loop] "=&r"(loop), [ret] "=&r"(ret),

		  [ptr] "+Q"(*(u32 *)ptr)

		: [val] "r" (val));

		break;

	case 8:

		asm ("//__percpu_xchg_8\n"

		"1:	ldxr	%[ret], %[ptr]\n"

		"	stxr	%w[loop], %[val], %[ptr]\n"

		"	cbnz	%w[loop], 1b"

		: [loop] "=&r"(loop), [ret] "=&r"(ret),

		  [ptr] "+Q"(*(u64 *)ptr)

		: [val] "r" (val));

		break;

	default:

		ret = 0;

		BUILD_BUG();

#define __PERCPU_OP_CASE(w, sfx, name, sz, op_llsc, op_lse)		\

static inline void							\

__percpu_##name##_case_##sz(void *ptr, unsigned long val)		\

{									\

	unsigned int loop;						\

	u##sz tmp;							\

									\

	asm volatile (ARM64_LSE_ATOMIC_INSN(				\

	/* LL/SC */							\

	"1:	ldxr" #sfx "\t%" #w "[tmp], %[ptr]\n"			\

		#op_llsc "\t%" #w "[tmp], %" #w "[tmp], %" #w "[val]\n"	\

	"	stxr" #sfx "\t%w[loop], %" #w "[tmp], %[ptr]\n"		\

	"	cbnz	%w[loop], 1b",					\

	/* LSE atomics */						\

		#op_lse "\t%" #w "[val], %[ptr]\n"			\

		__nops(3))						\

	: [loop] "=&r" (loop), [tmp] "=&r" (tmp),			\

	  [ptr] "+Q"(*(u##sz *)ptr)					\

	: [val] "r" ((u##sz)(val)));					\

}



	return ret;

#define __PERCPU_RET_OP_CASE(w, sfx, name, sz, op_llsc, op_lse)		\

static inline u##sz							\

__percpu_##name##_return_case_##sz(void *ptr, unsigned long val)	\

{									\

	unsigned int loop;						\

	u##sz ret;							\

									\

	asm volatile (ARM64_LSE_ATOMIC_INSN(				\

	/* LL/SC */							\

	"1:	ldxr" #sfx "\t%" #w "[ret], %[ptr]\n"			\

		#op_llsc "\t%" #w "[ret], %" #w "[ret], %" #w "[val]\n"	\

	"	stxr" #sfx "\t%w[loop], %" #w "[ret], %[ptr]\n"		\

	"	cbnz	%w[loop], 1b",					\

	/* LSE atomics */						\

		#op_lse "\t%" #w "[ret], %" #w "[val], %[ptr]\n"	\

		#op_llsc "\t%" #w "[ret], %" #w "[ret], %" #w "[val]\n"	\

		__nops(2))						\

	: [loop] "=&r" (loop), [ret] "=&r" (ret),			\

	  [ptr] "+Q"(*(u##sz *)ptr)					\

	: [val] "r" ((u##sz)(val)));					\

									\

	return ret;							\

}



/* this_cpu_cmpxchg */

#define _protect_cmpxchg_local(pcp, o, n)			\

({								\

	typeof(*raw_cpu_ptr(&(pcp))) __ret;			\

	preempt_disable();					\

	__ret = cmpxchg_local(raw_cpu_ptr(&(pcp)), o, n);	\

	preempt_enable();					\

	__ret;							\

})



#define this_cpu_cmpxchg_1(ptr, o, n) _protect_cmpxchg_local(ptr, o, n)

#define this_cpu_cmpxchg_2(ptr, o, n) _protect_cmpxchg_local(ptr, o, n)

#define this_cpu_cmpxchg_4(ptr, o, n) _protect_cmpxchg_local(ptr, o, n)

#define this_cpu_cmpxchg_8(ptr, o, n) _protect_cmpxchg_local(ptr, o, n)

#define PERCPU_OP(name, op_llsc, op_lse)				\

	__PERCPU_OP_CASE(w, b, name,  8, op_llsc, op_lse)		\

	__PERCPU_OP_CASE(w, h, name, 16, op_llsc, op_lse)		\

	__PERCPU_OP_CASE(w,  , name, 32, op_llsc, op_lse)		\

	__PERCPU_OP_CASE( ,  , name, 64, op_llsc, op_lse)



#define PERCPU_RET_OP(name, op_llsc, op_lse)				\

	__PERCPU_RET_OP_CASE(w, b, name,  8, op_llsc, op_lse)		\

	__PERCPU_RET_OP_CASE(w, h, name, 16, op_llsc, op_lse)		\

	__PERCPU_RET_OP_CASE(w,  , name, 32, op_llsc, op_lse)		\

	__PERCPU_RET_OP_CASE( ,  , name, 64, op_llsc, op_lse)



PERCPU_RW_OPS(8)

PERCPU_RW_OPS(16)

PERCPU_RW_OPS(32)

PERCPU_RW_OPS(64)

PERCPU_OP(add, add, stadd)

PERCPU_OP(andnot, bic, stclr)

PERCPU_OP(or, orr, stset)

PERCPU_RET_OP(add, add, ldadd)



#undef PERCPU_RW_OPS

#undef __PERCPU_OP_CASE

#undef __PERCPU_RET_OP_CASE

#undef PERCPU_OP

#undef PERCPU_RET_OP



/*

 * It would be nice to avoid the conditional call into the scheduler when

 * 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.

 */

#define this_cpu_cmpxchg_double_8(ptr1, ptr2, o1, o2, n1, n2)		\

({									\

	int __ret;							\

	preempt_disable();						\

	preempt_disable_notrace();					\

	__ret = cmpxchg_double_local(	raw_cpu_ptr(&(ptr1)),		\

					raw_cpu_ptr(&(ptr2)),		\

					o1, o2, n1, n2);		\

	preempt_enable();						\

	preempt_enable_notrace();					\

	__ret;								\

})



#define _percpu_read(pcp)						\

#define _pcp_protect(op, pcp, ...)					\

({									\

	typeof(pcp) __retval;						\

	preempt_disable_notrace();					\

	__retval = (typeof(pcp))__percpu_read(raw_cpu_ptr(&(pcp)), 	\

					      sizeof(pcp));		\

	op(raw_cpu_ptr(&(pcp)), __VA_ARGS__);				\

	preempt_enable_notrace();					\

	__retval;							\

})



#define _percpu_write(pcp, val)						\

do {									\

	preempt_disable_notrace();					\

	__percpu_write(raw_cpu_ptr(&(pcp)), (unsigned long)(val), 	\

				sizeof(pcp));				\

	preempt_enable_notrace();					\

} while(0)								\



#define _pcp_protect(operation, pcp, val)			\

#define _pcp_protect_return(op, pcp, args...)				\

({									\

	typeof(pcp) __retval;						\

	preempt_disable();					\

	__retval = (typeof(pcp))operation(raw_cpu_ptr(&(pcp)),	\

					  (val), sizeof(pcp));	\

	preempt_enable();					\

	preempt_disable_notrace();					\

	__retval = (typeof(pcp))op(raw_cpu_ptr(&(pcp)), ##args);	\

	preempt_enable_notrace();					\

	__retval;							\

})



#define _percpu_add(pcp, val) \

	_pcp_protect(__percpu_add, pcp, val)



#define _percpu_add_return(pcp, val) _percpu_add(pcp, val)



#define _percpu_and(pcp, val) \

	_pcp_protect(__percpu_and, pcp, val)



#define _percpu_or(pcp, val) \

	_pcp_protect(__percpu_or, pcp, val)



#define _percpu_xchg(pcp, val) (typeof(pcp)) \

	_pcp_protect(__percpu_xchg, pcp, (unsigned long)(val))



#define this_cpu_add_1(pcp, val) _percpu_add(pcp, val)

#define this_cpu_add_2(pcp, val) _percpu_add(pcp, val)

#define this_cpu_add_4(pcp, val) _percpu_add(pcp, val)

#define this_cpu_add_8(pcp, val) _percpu_add(pcp, val)



#define this_cpu_add_return_1(pcp, val) _percpu_add_return(pcp, val)

#define this_cpu_add_return_2(pcp, val) _percpu_add_return(pcp, val)

#define this_cpu_add_return_4(pcp, val) _percpu_add_return(pcp, val)

#define this_cpu_add_return_8(pcp, val) _percpu_add_return(pcp, val)



#define this_cpu_and_1(pcp, val) _percpu_and(pcp, val)

#define this_cpu_and_2(pcp, val) _percpu_and(pcp, val)

#define this_cpu_and_4(pcp, val) _percpu_and(pcp, val)

#define this_cpu_and_8(pcp, val) _percpu_and(pcp, val)



#define this_cpu_or_1(pcp, val) _percpu_or(pcp, val)

#define this_cpu_or_2(pcp, val) _percpu_or(pcp, val)

#define this_cpu_or_4(pcp, val) _percpu_or(pcp, val)

#define this_cpu_or_8(pcp, val) _percpu_or(pcp, val)



#define this_cpu_read_1(pcp) _percpu_read(pcp)

#define this_cpu_read_2(pcp) _percpu_read(pcp)

#define this_cpu_read_4(pcp) _percpu_read(pcp)

#define this_cpu_read_8(pcp) _percpu_read(pcp)



#define this_cpu_write_1(pcp, val) _percpu_write(pcp, val)

#define this_cpu_write_2(pcp, val) _percpu_write(pcp, val)

#define this_cpu_write_4(pcp, val) _percpu_write(pcp, val)

#define this_cpu_write_8(pcp, val) _percpu_write(pcp, val)



#define this_cpu_xchg_1(pcp, val) _percpu_xchg(pcp, val)

#define this_cpu_xchg_2(pcp, val) _percpu_xchg(pcp, val)

#define this_cpu_xchg_4(pcp, val) _percpu_xchg(pcp, val)

#define this_cpu_xchg_8(pcp, val) _percpu_xchg(pcp, val)

#define this_cpu_read_1(pcp)		\

	_pcp_protect_return(__percpu_read_8, pcp)

#define this_cpu_read_2(pcp)		\

	_pcp_protect_return(__percpu_read_16, pcp)

#define this_cpu_read_4(pcp)		\

	_pcp_protect_return(__percpu_read_32, pcp)

#define this_cpu_read_8(pcp)		\

	_pcp_protect_return(__percpu_read_64, pcp)



#define this_cpu_write_1(pcp, val)	\

	_pcp_protect(__percpu_write_8, pcp, (unsigned long)val)

#define this_cpu_write_2(pcp, val)	\

	_pcp_protect(__percpu_write_16, pcp, (unsigned long)val)

#define this_cpu_write_4(pcp, val)	\

	_pcp_protect(__percpu_write_32, pcp, (unsigned long)val)

#define this_cpu_write_8(pcp, val)	\

	_pcp_protect(__percpu_write_64, pcp, (unsigned long)val)



#define this_cpu_add_1(pcp, val)	\

	_pcp_protect(__percpu_add_case_8, pcp, val)

#define this_cpu_add_2(pcp, val)	\

	_pcp_protect(__percpu_add_case_16, pcp, val)

#define this_cpu_add_4(pcp, val)	\

	_pcp_protect(__percpu_add_case_32, pcp, val)

#define this_cpu_add_8(pcp, val)	\

	_pcp_protect(__percpu_add_case_64, pcp, val)



#define this_cpu_add_return_1(pcp, val)	\

	_pcp_protect_return(__percpu_add_return_case_8, pcp, val)

#define this_cpu_add_return_2(pcp, val)	\

	_pcp_protect_return(__percpu_add_return_case_16, pcp, val)

#define this_cpu_add_return_4(pcp, val)	\

	_pcp_protect_return(__percpu_add_return_case_32, pcp, val)

#define this_cpu_add_return_8(pcp, val)	\

	_pcp_protect_return(__percpu_add_return_case_64, pcp, val)



#define this_cpu_and_1(pcp, val)	\

	_pcp_protect(__percpu_andnot_case_8, pcp, ~val)

#define this_cpu_and_2(pcp, val)	\

	_pcp_protect(__percpu_andnot_case_16, pcp, ~val)

#define this_cpu_and_4(pcp, val)	\

	_pcp_protect(__percpu_andnot_case_32, pcp, ~val)

#define this_cpu_and_8(pcp, val)	\

	_pcp_protect(__percpu_andnot_case_64, pcp, ~val)



#define this_cpu_or_1(pcp, val)		\

	_pcp_protect(__percpu_or_case_8, pcp, val)

#define this_cpu_or_2(pcp, val)		\

	_pcp_protect(__percpu_or_case_16, pcp, val)

#define this_cpu_or_4(pcp, val)		\

	_pcp_protect(__percpu_or_case_32, pcp, val)

#define this_cpu_or_8(pcp, val)		\

	_pcp_protect(__percpu_or_case_64, pcp, val)



#define this_cpu_xchg_1(pcp, val)	\

	_pcp_protect_return(xchg_relaxed, pcp, val)

#define this_cpu_xchg_2(pcp, val)	\

	_pcp_protect_return(xchg_relaxed, pcp, val)

#define this_cpu_xchg_4(pcp, val)	\

	_pcp_protect_return(xchg_relaxed, pcp, val)

#define this_cpu_xchg_8(pcp, val)	\

	_pcp_protect_return(xchg_relaxed, pcp, val)



#define this_cpu_cmpxchg_1(pcp, o, n)	\

	_pcp_protect_return(cmpxchg_relaxed, pcp, o, n)

#define this_cpu_cmpxchg_2(pcp, o, n)	\

	_pcp_protect_return(cmpxchg_relaxed, pcp, o, n)

#define this_cpu_cmpxchg_4(pcp, o, n)	\

	_pcp_protect_return(cmpxchg_relaxed, pcp, o, n)

#define this_cpu_cmpxchg_8(pcp, o, n)	\

	_pcp_protect_return(cmpxchg_relaxed, pcp, o, n)



#include <asm-generic/percpu.h>