linux/arch/x86/include/asm/preempt.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __ASM_PREEMPT_H
#define __ASM_PREEMPT_H

#include <asm/rmwcc.h>
#include <asm/percpu.h>

#include <linux/static_call_types.h>

DECLARE_PER_CPU_CACHE_HOT(unsigned long, __preempt_count);

/*
 * We use the MSB for PREEMPT_NEED_RESCHED mostly because it is available.
 */
#define PREEMPT_NEED_RESCHED	(~(((unsigned long)-1L) >> 1))

#ifdef CONFIG_HAS_SEPARATE_PREEMPT_RESCHED_BITS
#define __pc_dec		"decq"
#define __pc_op(op, ...)	raw_cpu_##op##_8(__VA_ARGS__)
#else
#define __pc_dec		"decl"
#define __pc_op(op, ...)	raw_cpu_##op##_4(__VA_ARGS__)
#endif

/*
 * We use the PREEMPT_NEED_RESCHED bit as an inverted NEED_RESCHED such
 * that a decrement hitting 0 means we can and should reschedule.
 */
#define PREEMPT_ENABLED	(0 + PREEMPT_NEED_RESCHED)

/*
 * We mask the PREEMPT_NEED_RESCHED bit so as not to confuse all current users
 * that think a non-zero value indicates we cannot preempt.
 */
static __always_inline int preempt_count(void)
{
	return __pc_op(read, __preempt_count) & ~PREEMPT_NEED_RESCHED;
}

/*
 * unsigned long preempt count parameter works for both 32bit and 64bit cases:
 *
 * - For 32bit, "int" (the return of preempt_count()) and "unsigned long" have
 *   the same size.
 * - For 64bit, the effective bits of a preempt count sit in 32bit, and we
 *   preserve the NEED_RESCHED bit from the old count.
 */
static __always_inline void preempt_count_set(unsigned long pc)
{
	unsigned long old, new;

	old = __pc_op(read, __preempt_count);
	do {
		new = (old & PREEMPT_NEED_RESCHED) |
			(pc & ~PREEMPT_NEED_RESCHED);
	} while (!__pc_op(try_cmpxchg, __preempt_count, &old, new));
}

/*
 * must be macros to avoid header recursion hell
 */
#define init_task_preempt_count(p) do { } while (0)

#define init_idle_preempt_count(p, cpu) do { \
	per_cpu(__preempt_count, (cpu)) = PREEMPT_DISABLED; \
} while (0)

/*
 * We fold the NEED_RESCHED bit into the preempt count such that
 * preempt_enable() can decrement and test for needing to reschedule with a
 * single instruction.
 *
 * We invert the actual bit, so that when the decrement hits 0 we know we both
 * need to resched (the bit is cleared) and can resched (no preempt count).
 */

static __always_inline void set_preempt_need_resched(void)
{
	__pc_op(and, __preempt_count, ~PREEMPT_NEED_RESCHED);
}

static __always_inline void clear_preempt_need_resched(void)
{
	__pc_op(or, __preempt_count, PREEMPT_NEED_RESCHED);
}

static __always_inline bool test_preempt_need_resched(void)
{
	return !(__pc_op(read, __preempt_count) & PREEMPT_NEED_RESCHED);
}

/*
 * The various preempt_count add/sub methods
 */

static __always_inline void __preempt_count_add(int val)
{
	__pc_op(add, __preempt_count, val);
}

static __always_inline void __preempt_count_sub(int val)
{
	__pc_op(add, __preempt_count, -val);
}

static __always_inline int __preempt_count_add_return(int val)
{
	return __pc_op(add_return, __preempt_count, val);
}

static __always_inline int __preempt_count_sub_return(int val)
{
	return __pc_op(add_return, __preempt_count, -val);
}

/*
 * Because we keep PREEMPT_NEED_RESCHED set when we do _not_ need to reschedule
 * a decrement which hits zero means we have no preempt_count and should
 * reschedule.
 */
static __always_inline bool __preempt_count_dec_and_test(void)
{
	return GEN_UNARY_RMWcc(__pc_dec, __my_cpu_var(__preempt_count), e,
			       __percpu_arg([var]));
}

/*
 * Returns true when we need to resched and can (barring IRQ state).
 */
static __always_inline bool should_resched(int preempt_offset)
{
	return unlikely(__pc_op(read, __preempt_count) == preempt_offset);
}

#ifdef CONFIG_PREEMPTION

extern asmlinkage void preempt_schedule(void);
extern asmlinkage void preempt_schedule_thunk(void);

#define preempt_schedule_dynamic_enabled	preempt_schedule_thunk
#define preempt_schedule_dynamic_disabled	NULL

extern asmlinkage void preempt_schedule_notrace(void);
extern asmlinkage void preempt_schedule_notrace_thunk(void);

#define preempt_schedule_notrace_dynamic_enabled	preempt_schedule_notrace_thunk
#define preempt_schedule_notrace_dynamic_disabled	NULL

#ifdef CONFIG_PREEMPT_DYNAMIC

DECLARE_STATIC_CALL(preempt_schedule, preempt_schedule_dynamic_enabled);

#define __preempt_schedule() \
do { \
	__STATIC_CALL_MOD_ADDRESSABLE(preempt_schedule); \
	asm volatile ("call " STATIC_CALL_TRAMP_STR(preempt_schedule) : ASM_CALL_CONSTRAINT); \
} while (0)

DECLARE_STATIC_CALL(preempt_schedule_notrace, preempt_schedule_notrace_dynamic_enabled);

#define __preempt_schedule_notrace() \
do { \
	__STATIC_CALL_MOD_ADDRESSABLE(preempt_schedule_notrace); \
	asm volatile ("call " STATIC_CALL_TRAMP_STR(preempt_schedule_notrace) : ASM_CALL_CONSTRAINT); \
} while (0)

#else /* PREEMPT_DYNAMIC */

#define __preempt_schedule() \
	asm volatile ("call preempt_schedule_thunk" : ASM_CALL_CONSTRAINT);

#define __preempt_schedule_notrace() \
	asm volatile ("call preempt_schedule_notrace_thunk" : ASM_CALL_CONSTRAINT);

#endif /* PREEMPT_DYNAMIC */

#endif /* PREEMPTION */

#undef __pc_op
#undef __pc_dec

#endif /* __ASM_PREEMPT_H */