cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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trace_clock.c (4323B)

      1// SPDX-License-Identifier: GPL-2.0
      2/*
      3 * tracing clocks
      4 *
      5 *  Copyright (C) 2009 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
      6 *
      7 * Implements 3 trace clock variants, with differing scalability/precision
      8 * tradeoffs:
      9 *
     10 *  -   local: CPU-local trace clock
     11 *  -  medium: scalable global clock with some jitter
     12 *  -  global: globally monotonic, serialized clock
     13 *
     14 * Tracer plugins will chose a default from these clocks.
     15 */
     16#include <linux/spinlock.h>
     17#include <linux/irqflags.h>
     18#include <linux/hardirq.h>
     19#include <linux/module.h>
     20#include <linux/percpu.h>
     21#include <linux/sched.h>
     22#include <linux/sched/clock.h>
     23#include <linux/ktime.h>
     24#include <linux/trace_clock.h>
     25
     26/*
     27 * trace_clock_local(): the simplest and least coherent tracing clock.
     28 *
     29 * Useful for tracing that does not cross to other CPUs nor
     30 * does it go through idle events.
     31 */
     32u64 notrace trace_clock_local(void)
     33{
     34	u64 clock;
     35
     36	/*
     37	 * sched_clock() is an architecture implemented, fast, scalable,
     38	 * lockless clock. It is not guaranteed to be coherent across
     39	 * CPUs, nor across CPU idle events.
     40	 */
     41	preempt_disable_notrace();
     42	clock = sched_clock();
     43	preempt_enable_notrace();
     44
     45	return clock;
     46}
     47EXPORT_SYMBOL_GPL(trace_clock_local);
     48
     49/*
     50 * trace_clock(): 'between' trace clock. Not completely serialized,
     51 * but not completely incorrect when crossing CPUs either.
     52 *
     53 * This is based on cpu_clock(), which will allow at most ~1 jiffy of
     54 * jitter between CPUs. So it's a pretty scalable clock, but there
     55 * can be offsets in the trace data.
     56 */
     57u64 notrace trace_clock(void)
     58{
     59	return local_clock();
     60}
     61EXPORT_SYMBOL_GPL(trace_clock);
     62
     63/*
     64 * trace_jiffy_clock(): Simply use jiffies as a clock counter.
     65 * Note that this use of jiffies_64 is not completely safe on
     66 * 32-bit systems. But the window is tiny, and the effect if
     67 * we are affected is that we will have an obviously bogus
     68 * timestamp on a trace event - i.e. not life threatening.
     69 */
     70u64 notrace trace_clock_jiffies(void)
     71{
     72	return jiffies_64_to_clock_t(jiffies_64 - INITIAL_JIFFIES);
     73}
     74EXPORT_SYMBOL_GPL(trace_clock_jiffies);
     75
     76/*
     77 * trace_clock_global(): special globally coherent trace clock
     78 *
     79 * It has higher overhead than the other trace clocks but is still
     80 * an order of magnitude faster than GTOD derived hardware clocks.
     81 *
     82 * Used by plugins that need globally coherent timestamps.
     83 */
     84
     85/* keep prev_time and lock in the same cacheline. */
     86static struct {
     87	u64 prev_time;
     88	arch_spinlock_t lock;
     89} trace_clock_struct ____cacheline_aligned_in_smp =
     90	{
     91		.lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED,
     92	};
     93
     94u64 notrace trace_clock_global(void)
     95{
     96	unsigned long flags;
     97	int this_cpu;
     98	u64 now, prev_time;
     99
    100	raw_local_irq_save(flags);
    101
    102	this_cpu = raw_smp_processor_id();
    103
    104	/*
    105	 * The global clock "guarantees" that the events are ordered
    106	 * between CPUs. But if two events on two different CPUS call
    107	 * trace_clock_global at roughly the same time, it really does
    108	 * not matter which one gets the earlier time. Just make sure
    109	 * that the same CPU will always show a monotonic clock.
    110	 *
    111	 * Use a read memory barrier to get the latest written
    112	 * time that was recorded.
    113	 */
    114	smp_rmb();
    115	prev_time = READ_ONCE(trace_clock_struct.prev_time);
    116	now = sched_clock_cpu(this_cpu);
    117
    118	/* Make sure that now is always greater than or equal to prev_time */
    119	if ((s64)(now - prev_time) < 0)
    120		now = prev_time;
    121
    122	/*
    123	 * If in an NMI context then dont risk lockups and simply return
    124	 * the current time.
    125	 */
    126	if (unlikely(in_nmi()))
    127		goto out;
    128
    129	/* Tracing can cause strange recursion, always use a try lock */
    130	if (arch_spin_trylock(&trace_clock_struct.lock)) {
    131		/* Reread prev_time in case it was already updated */
    132		prev_time = READ_ONCE(trace_clock_struct.prev_time);
    133		if ((s64)(now - prev_time) < 0)
    134			now = prev_time;
    135
    136		trace_clock_struct.prev_time = now;
    137
    138		/* The unlock acts as the wmb for the above rmb */
    139		arch_spin_unlock(&trace_clock_struct.lock);
    140	}
    141 out:
    142	raw_local_irq_restore(flags);
    143
    144	return now;
    145}
    146EXPORT_SYMBOL_GPL(trace_clock_global);
    147
    148static atomic64_t trace_counter;
    149
    150/*
    151 * trace_clock_counter(): simply an atomic counter.
    152 * Use the trace_counter "counter" for cases where you do not care
    153 * about timings, but are interested in strict ordering.
    154 */
    155u64 notrace trace_clock_counter(void)
    156{
    157	return atomic64_add_return(1, &trace_counter);
    158}