context_tracking_state.h

  1/* SPDX-License-Identifier: GPL-2.0 */
  2#ifndef _LINUX_CONTEXT_TRACKING_STATE_H
  3#define _LINUX_CONTEXT_TRACKING_STATE_H
  4
  5#include <linux/percpu.h>
  6#include <linux/static_key.h>
  7#include <linux/context_tracking_irq.h>
  8
  9/* Offset to allow distinguishing irq vs. task-based idle entry/exit. */
 10#define CT_NESTING_IRQ_NONIDLE	((LONG_MAX / 2) + 1)
 11
 12enum ctx_state {
 13	CT_STATE_DISABLED	= -1,	/* returned by ct_state() if unknown */
 14	CT_STATE_KERNEL		= 0,
 15	CT_STATE_IDLE		= 1,
 16	CT_STATE_USER		= 2,
 17	CT_STATE_GUEST		= 3,
 18	CT_STATE_MAX		= 4,
 19};
 20
 21struct context_tracking {
 22#ifdef CONFIG_CONTEXT_TRACKING_USER
 23	/*
 24	 * When active is false, probes are unset in order
 25	 * to minimize overhead: TIF flags are cleared
 26	 * and calls to user_enter/exit are ignored. This
 27	 * may be further optimized using static keys.
 28	 */
 29	bool active;
 30	int recursion;
 31#endif
 32#ifdef CONFIG_CONTEXT_TRACKING
 33	atomic_t state;
 34#endif
 35#ifdef CONFIG_CONTEXT_TRACKING_IDLE
 36	long nesting;		/* Track process nesting level. */
 37	long nmi_nesting;	/* Track irq/NMI nesting level. */
 38#endif
 39};
 40
 41/*
 42 * We cram two different things within the same atomic variable:
 43 *
 44 *                     CT_RCU_WATCHING_START  CT_STATE_START
 45 *                                |                |
 46 *                                v                v
 47 *     MSB [ RCU watching counter ][ context_state ] LSB
 48 *         ^                       ^
 49 *         |                       |
 50 * CT_RCU_WATCHING_END        CT_STATE_END
 51 *
 52 * Bits are used from the LSB upwards, so unused bits (if any) will always be in
 53 * upper bits of the variable.
 54 */
 55#ifdef CONFIG_CONTEXT_TRACKING
 56#define CT_SIZE (sizeof(((struct context_tracking *)0)->state) * BITS_PER_BYTE)
 57
 58#define CT_STATE_WIDTH bits_per(CT_STATE_MAX - 1)
 59#define CT_STATE_START 0
 60#define CT_STATE_END   (CT_STATE_START + CT_STATE_WIDTH - 1)
 61
 62#define CT_RCU_WATCHING_MAX_WIDTH (CT_SIZE - CT_STATE_WIDTH)
 63#define CT_RCU_WATCHING_WIDTH     (IS_ENABLED(CONFIG_RCU_DYNTICKS_TORTURE) ? 2 : CT_RCU_WATCHING_MAX_WIDTH)
 64#define CT_RCU_WATCHING_START     (CT_STATE_END + 1)
 65#define CT_RCU_WATCHING_END       (CT_RCU_WATCHING_START + CT_RCU_WATCHING_WIDTH - 1)
 66#define CT_RCU_WATCHING           BIT(CT_RCU_WATCHING_START)
 67
 68#define CT_STATE_MASK        GENMASK(CT_STATE_END,        CT_STATE_START)
 69#define CT_RCU_WATCHING_MASK GENMASK(CT_RCU_WATCHING_END, CT_RCU_WATCHING_START)
 70
 71#define CT_UNUSED_WIDTH (CT_RCU_WATCHING_MAX_WIDTH - CT_RCU_WATCHING_WIDTH)
 72
 73static_assert(CT_STATE_WIDTH        +
 74	      CT_RCU_WATCHING_WIDTH +
 75	      CT_UNUSED_WIDTH       ==
 76	      CT_SIZE);
 77
 78DECLARE_PER_CPU(struct context_tracking, context_tracking);
 79#endif	/* CONFIG_CONTEXT_TRACKING */
 80
 81#ifdef CONFIG_CONTEXT_TRACKING_USER
 82static __always_inline int __ct_state(void)
 83{
 84	return raw_atomic_read(this_cpu_ptr(&context_tracking.state)) & CT_STATE_MASK;
 85}
 86#endif
 87
 88#ifdef CONFIG_CONTEXT_TRACKING_IDLE
 89static __always_inline int ct_rcu_watching(void)
 90{
 91	return atomic_read(this_cpu_ptr(&context_tracking.state)) & CT_RCU_WATCHING_MASK;
 92}
 93
 94static __always_inline int ct_rcu_watching_cpu(int cpu)
 95{
 96	struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
 97
 98	return atomic_read(&ct->state) & CT_RCU_WATCHING_MASK;
 99}
100
101static __always_inline int ct_rcu_watching_cpu_acquire(int cpu)
102{
103	struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
104
105	return atomic_read_acquire(&ct->state) & CT_RCU_WATCHING_MASK;
106}
107
108static __always_inline long ct_nesting(void)
109{
110	return __this_cpu_read(context_tracking.nesting);
111}
112
113static __always_inline long ct_nesting_cpu(int cpu)
114{
115	struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
116
117	return ct->nesting;
118}
119
120static __always_inline long ct_nmi_nesting(void)
121{
122	return __this_cpu_read(context_tracking.nmi_nesting);
123}
124
125static __always_inline long ct_nmi_nesting_cpu(int cpu)
126{
127	struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
128
129	return ct->nmi_nesting;
130}
131#endif /* #ifdef CONFIG_CONTEXT_TRACKING_IDLE */
132
133#ifdef CONFIG_CONTEXT_TRACKING_USER
134extern struct static_key_false context_tracking_key;
135
136static __always_inline bool context_tracking_enabled(void)
137{
138	return static_branch_unlikely(&context_tracking_key);
139}
140
141static __always_inline bool context_tracking_enabled_cpu(int cpu)
142{
143	return context_tracking_enabled() && per_cpu(context_tracking.active, cpu);
144}
145
146static __always_inline bool context_tracking_enabled_this_cpu(void)
147{
148	return context_tracking_enabled() && __this_cpu_read(context_tracking.active);
149}
150
151/**
152 * ct_state() - return the current context tracking state if known
153 *
154 * Returns the current cpu's context tracking state if context tracking
155 * is enabled.  If context tracking is disabled, returns
156 * CT_STATE_DISABLED.  This should be used primarily for debugging.
157 */
158static __always_inline int ct_state(void)
159{
160	int ret;
161
162	if (!context_tracking_enabled())
163		return CT_STATE_DISABLED;
164
165	preempt_disable();
166	ret = __ct_state();
167	preempt_enable();
168
169	return ret;
170}
171
172#else
173static __always_inline bool context_tracking_enabled(void) { return false; }
174static __always_inline bool context_tracking_enabled_cpu(int cpu) { return false; }
175static __always_inline bool context_tracking_enabled_this_cpu(void) { return false; }
176#endif /* CONFIG_CONTEXT_TRACKING_USER */
177
178#endif