Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1098 insertions, 0 deletions

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
new file mode 100644
index 000000000..95fc77853
--- /dev/null
+++ b/kernel/sched/cputime.c
@@ -0,0 +1,1098 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Simple CPU accounting cgroup controller
+ */
+
+#ifdef CONFIG_IRQ_TIME_ACCOUNTING
+
+/*
+ * There are no locks covering percpu hardirq/softirq time.
+ * They are only modified in vtime_account, on corresponding CPU
+ * with interrupts disabled. So, writes are safe.
+ * They are read and saved off onto struct rq in update_rq_clock().
+ * This may result in other CPU reading this CPU's irq time and can
+ * race with irq/vtime_account on this CPU. We would either get old
+ * or new value with a side effect of accounting a slice of irq time to wrong
+ * task when irq is in progress while we read rq->clock. That is a worthy
+ * compromise in place of having locks on each irq in account_system_time.
+ */
+DEFINE_PER_CPU(struct irqtime, cpu_irqtime);
+
+static int sched_clock_irqtime;
+
+void enable_sched_clock_irqtime(void)
+{
+	sched_clock_irqtime = 1;
+}
+
+void disable_sched_clock_irqtime(void)
+{
+	sched_clock_irqtime = 0;
+}
+
+static void irqtime_account_delta(struct irqtime *irqtime, u64 delta,
+				  enum cpu_usage_stat idx)
+{
+	u64 *cpustat = kcpustat_this_cpu->cpustat;
+
+	u64_stats_update_begin(&irqtime->sync);
+	cpustat[idx] += delta;
+	irqtime->total += delta;
+	irqtime->tick_delta += delta;
+	u64_stats_update_end(&irqtime->sync);
+}
+
+/*
+ * Called after incrementing preempt_count on {soft,}irq_enter
+ * and before decrementing preempt_count on {soft,}irq_exit.
+ */
+void irqtime_account_irq(struct task_struct *curr, unsigned int offset)
+{
+	struct irqtime *irqtime = this_cpu_ptr(&cpu_irqtime);
+	unsigned int pc;
+	s64 delta;
+	int cpu;
+
+	if (!sched_clock_irqtime)
+		return;
+
+	cpu = smp_processor_id();
+	delta = sched_clock_cpu(cpu) - irqtime->irq_start_time;
+	irqtime->irq_start_time += delta;
+	pc = irq_count() - offset;
+
+	/*
+	 * We do not account for softirq time from ksoftirqd here.
+	 * We want to continue accounting softirq time to ksoftirqd thread
+	 * in that case, so as not to confuse scheduler with a special task
+	 * that do not consume any time, but still wants to run.
+	 */
+	if (pc & HARDIRQ_MASK)
+		irqtime_account_delta(irqtime, delta, CPUTIME_IRQ);
+	else if ((pc & SOFTIRQ_OFFSET) && curr != this_cpu_ksoftirqd())
+		irqtime_account_delta(irqtime, delta, CPUTIME_SOFTIRQ);
+}
+
+static u64 irqtime_tick_accounted(u64 maxtime)
+{
+	struct irqtime *irqtime = this_cpu_ptr(&cpu_irqtime);
+	u64 delta;
+
+	delta = min(irqtime->tick_delta, maxtime);
+	irqtime->tick_delta -= delta;
+
+	return delta;
+}
+
+#else /* CONFIG_IRQ_TIME_ACCOUNTING */
+
+#define sched_clock_irqtime	(0)
+
+static u64 irqtime_tick_accounted(u64 dummy)
+{
+	return 0;
+}
+
+#endif /* !CONFIG_IRQ_TIME_ACCOUNTING */
+
+static inline void task_group_account_field(struct task_struct *p, int index,
+					    u64 tmp)
+{
+	/*
+	 * Since all updates are sure to touch the root cgroup, we
+	 * get ourselves ahead and touch it first. If the root cgroup
+	 * is the only cgroup, then nothing else should be necessary.
+	 *
+	 */
+	__this_cpu_add(kernel_cpustat.cpustat[index], tmp);
+
+	cgroup_account_cputime_field(p, index, tmp);
+}
+
+/*
+ * Account user CPU time to a process.
+ * @p: the process that the CPU time gets accounted to
+ * @cputime: the CPU time spent in user space since the last update
+ */
+void account_user_time(struct task_struct *p, u64 cputime)
+{
+	int index;
+
+	/* Add user time to process. */
+	p->utime += cputime;
+	account_group_user_time(p, cputime);
+
+	index = (task_nice(p) > 0) ? CPUTIME_NICE : CPUTIME_USER;
+
+	/* Add user time to cpustat. */
+	task_group_account_field(p, index, cputime);
+
+	/* Account for user time used */
+	acct_account_cputime(p);
+}
+
+/*
+ * Account guest CPU time to a process.
+ * @p: the process that the CPU time gets accounted to
+ * @cputime: the CPU time spent in virtual machine since the last update
+ */
+void account_guest_time(struct task_struct *p, u64 cputime)
+{
+	u64 *cpustat = kcpustat_this_cpu->cpustat;
+
+	/* Add guest time to process. */
+	p->utime += cputime;
+	account_group_user_time(p, cputime);
+	p->gtime += cputime;
+
+	/* Add guest time to cpustat. */
+	if (task_nice(p) > 0) {
+		task_group_account_field(p, CPUTIME_NICE, cputime);
+		cpustat[CPUTIME_GUEST_NICE] += cputime;
+	} else {
+		task_group_account_field(p, CPUTIME_USER, cputime);
+		cpustat[CPUTIME_GUEST] += cputime;
+	}
+}
+
+/*
+ * Account system CPU time to a process and desired cpustat field
+ * @p: the process that the CPU time gets accounted to
+ * @cputime: the CPU time spent in kernel space since the last update
+ * @index: pointer to cpustat field that has to be updated
+ */
+void account_system_index_time(struct task_struct *p,
+			       u64 cputime, enum cpu_usage_stat index)
+{
+	/* Add system time to process. */
+	p->stime += cputime;
+	account_group_system_time(p, cputime);
+
+	/* Add system time to cpustat. */
+	task_group_account_field(p, index, cputime);
+
+	/* Account for system time used */
+	acct_account_cputime(p);
+}
+
+/*
+ * Account system CPU time to a process.
+ * @p: the process that the CPU time gets accounted to
+ * @hardirq_offset: the offset to subtract from hardirq_count()
+ * @cputime: the CPU time spent in kernel space since the last update
+ */
+void account_system_time(struct task_struct *p, int hardirq_offset, u64 cputime)
+{
+	int index;
+
+	if ((p->flags & PF_VCPU) && (irq_count() - hardirq_offset == 0)) {
+		account_guest_time(p, cputime);
+		return;
+	}
+
+	if (hardirq_count() - hardirq_offset)
+		index = CPUTIME_IRQ;
+	else if (in_serving_softirq())
+		index = CPUTIME_SOFTIRQ;
+	else
+		index = CPUTIME_SYSTEM;
+
+	account_system_index_time(p, cputime, index);
+}
+
+/*
+ * Account for involuntary wait time.
+ * @cputime: the CPU time spent in involuntary wait
+ */
+void account_steal_time(u64 cputime)
+{
+	u64 *cpustat = kcpustat_this_cpu->cpustat;
+
+	cpustat[CPUTIME_STEAL] += cputime;
+}
+
+/*
+ * Account for idle time.
+ * @cputime: the CPU time spent in idle wait
+ */
+void account_idle_time(u64 cputime)
+{
+	u64 *cpustat = kcpustat_this_cpu->cpustat;
+	struct rq *rq = this_rq();
+
+	if (atomic_read(&rq->nr_iowait) > 0)
+		cpustat[CPUTIME_IOWAIT] += cputime;
+	else
+		cpustat[CPUTIME_IDLE] += cputime;
+}
+
+
+#ifdef CONFIG_SCHED_CORE
+/*
+ * Account for forceidle time due to core scheduling.
+ *
+ * REQUIRES: schedstat is enabled.
+ */
+void __account_forceidle_time(struct task_struct *p, u64 delta)
+{
+	__schedstat_add(p->stats.core_forceidle_sum, delta);
+
+	task_group_account_field(p, CPUTIME_FORCEIDLE, delta);
+}
+#endif
+
+/*
+ * When a guest is interrupted for a longer amount of time, missed clock
+ * ticks are not redelivered later. Due to that, this function may on
+ * occasion account more time than the calling functions think elapsed.
+ */
+static __always_inline u64 steal_account_process_time(u64 maxtime)
+{
+#ifdef CONFIG_PARAVIRT
+	if (static_key_false(&paravirt_steal_enabled)) {
+		u64 steal;
+
+		steal = paravirt_steal_clock(smp_processor_id());
+		steal -= this_rq()->prev_steal_time;
+		steal = min(steal, maxtime);
+		account_steal_time(steal);
+		this_rq()->prev_steal_time += steal;
+
+		return steal;
+	}
+#endif
+	return 0;
+}
+
+/*
+ * Account how much elapsed time was spent in steal, irq, or softirq time.
+ */
+static inline u64 account_other_time(u64 max)
+{
+	u64 accounted;
+
+	lockdep_assert_irqs_disabled();
+
+	accounted = steal_account_process_time(max);
+
+	if (accounted < max)
+		accounted += irqtime_tick_accounted(max - accounted);
+
+	return accounted;
+}
+
+#ifdef CONFIG_64BIT
+static inline u64 read_sum_exec_runtime(struct task_struct *t)
+{
+	return t->se.sum_exec_runtime;
+}
+#else
+static u64 read_sum_exec_runtime(struct task_struct *t)
+{
+	u64 ns;
+	struct rq_flags rf;
+	struct rq *rq;
+
+	rq = task_rq_lock(t, &rf);
+	ns = t->se.sum_exec_runtime;
+	task_rq_unlock(rq, t, &rf);
+
+	return ns;
+}
+#endif
+
+/*
+ * Accumulate raw cputime values of dead tasks (sig->[us]time) and live
+ * tasks (sum on group iteration) belonging to @tsk's group.
+ */
+void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times)
+{
+	struct signal_struct *sig = tsk->signal;
+	u64 utime, stime;
+	struct task_struct *t;
+	unsigned int seq, nextseq;
+	unsigned long flags;
+
+	/*
+	 * Update current task runtime to account pending time since last
+	 * scheduler action or thread_group_cputime() call. This thread group
+	 * might have other running tasks on different CPUs, but updating
+	 * their runtime can affect syscall performance, so we skip account
+	 * those pending times and rely only on values updated on tick or
+	 * other scheduler action.
+	 */
+	if (same_thread_group(current, tsk))
+		(void) task_sched_runtime(current);
+
+	rcu_read_lock();
+	/* Attempt a lockless read on the first round. */
+	nextseq = 0;
+	do {
+		seq = nextseq;
+		flags = read_seqbegin_or_lock_irqsave(&sig->stats_lock, &seq);
+		times->utime = sig->utime;
+		times->stime = sig->stime;
+		times->sum_exec_runtime = sig->sum_sched_runtime;
+
+		for_each_thread(tsk, t) {
+			task_cputime(t, &utime, &stime);
+			times->utime += utime;
+			times->stime += stime;
+			times->sum_exec_runtime += read_sum_exec_runtime(t);
+		}
+		/* If lockless access failed, take the lock. */
+		nextseq = 1;
+	} while (need_seqretry(&sig->stats_lock, seq));
+	done_seqretry_irqrestore(&sig->stats_lock, seq, flags);
+	rcu_read_unlock();
+}
+
+#ifdef CONFIG_IRQ_TIME_ACCOUNTING
+/*
+ * Account a tick to a process and cpustat
+ * @p: the process that the CPU time gets accounted to
+ * @user_tick: is the tick from userspace
+ * @rq: the pointer to rq
+ *
+ * Tick demultiplexing follows the order
+ * - pending hardirq update
+ * - pending softirq update
+ * - user_time
+ * - idle_time
+ * - system time
+ *   - check for guest_time
+ *   - else account as system_time
+ *
+ * Check for hardirq is done both for system and user time as there is
+ * no timer going off while we are on hardirq and hence we may never get an
+ * opportunity to update it solely in system time.
+ * p->stime and friends are only updated on system time and not on irq
+ * softirq as those do not count in task exec_runtime any more.
+ */
+static void irqtime_account_process_tick(struct task_struct *p, int user_tick,
+					 int ticks)
+{
+	u64 other, cputime = TICK_NSEC * ticks;
+
+	/*
+	 * When returning from idle, many ticks can get accounted at
+	 * once, including some ticks of steal, irq, and softirq time.
+	 * Subtract those ticks from the amount of time accounted to
+	 * idle, or potentially user or system time. Due to rounding,
+	 * other time can exceed ticks occasionally.
+	 */
+	other = account_other_time(ULONG_MAX);
+	if (other >= cputime)
+		return;
+
+	cputime -= other;
+
+	if (this_cpu_ksoftirqd() == p) {
+		/*
+		 * ksoftirqd time do not get accounted in cpu_softirq_time.
+		 * So, we have to handle it separately here.
+		 * Also, p->stime needs to be updated for ksoftirqd.
+		 */
+		account_system_index_time(p, cputime, CPUTIME_SOFTIRQ);
+	} else if (user_tick) {
+		account_user_time(p, cputime);
+	} else if (p == this_rq()->idle) {
+		account_idle_time(cputime);
+	} else if (p->flags & PF_VCPU) { /* System time or guest time */
+		account_guest_time(p, cputime);
+	} else {
+		account_system_index_time(p, cputime, CPUTIME_SYSTEM);
+	}
+}
+
+static void irqtime_account_idle_ticks(int ticks)
+{
+	irqtime_account_process_tick(current, 0, ticks);
+}
+#else /* CONFIG_IRQ_TIME_ACCOUNTING */
+static inline void irqtime_account_idle_ticks(int ticks) { }
+static inline void irqtime_account_process_tick(struct task_struct *p, int user_tick,
+						int nr_ticks) { }
+#endif /* CONFIG_IRQ_TIME_ACCOUNTING */
+
+/*
+ * Use precise platform statistics if available:
+ */
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
+
+# ifndef __ARCH_HAS_VTIME_TASK_SWITCH
+void vtime_task_switch(struct task_struct *prev)
+{
+	if (is_idle_task(prev))
+		vtime_account_idle(prev);
+	else
+		vtime_account_kernel(prev);
+
+	vtime_flush(prev);
+	arch_vtime_task_switch(prev);
+}
+# endif
+
+void vtime_account_irq(struct task_struct *tsk, unsigned int offset)
+{
+	unsigned int pc = irq_count() - offset;
+
+	if (pc & HARDIRQ_OFFSET) {
+		vtime_account_hardirq(tsk);
+	} else if (pc & SOFTIRQ_OFFSET) {
+		vtime_account_softirq(tsk);
+	} else if (!IS_ENABLED(CONFIG_HAVE_VIRT_CPU_ACCOUNTING_IDLE) &&
+		   is_idle_task(tsk)) {
+		vtime_account_idle(tsk);
+	} else {
+		vtime_account_kernel(tsk);
+	}
+}
+
+void cputime_adjust(struct task_cputime *curr, struct prev_cputime *prev,
+		    u64 *ut, u64 *st)
+{
+	*ut = curr->utime;
+	*st = curr->stime;
+}
+
+void task_cputime_adjusted(struct task_struct *p, u64 *ut, u64 *st)
+{
+	*ut = p->utime;
+	*st = p->stime;
+}
+EXPORT_SYMBOL_GPL(task_cputime_adjusted);
+
+void thread_group_cputime_adjusted(struct task_struct *p, u64 *ut, u64 *st)
+{
+	struct task_cputime cputime;
+
+	thread_group_cputime(p, &cputime);
+
+	*ut = cputime.utime;
+	*st = cputime.stime;
+}
+
+#else /* !CONFIG_VIRT_CPU_ACCOUNTING_NATIVE: */
+
+/*
+ * Account a single tick of CPU time.
+ * @p: the process that the CPU time gets accounted to
+ * @user_tick: indicates if the tick is a user or a system tick
+ */
+void account_process_tick(struct task_struct *p, int user_tick)
+{
+	u64 cputime, steal;
+
+	if (vtime_accounting_enabled_this_cpu())
+		return;
+
+	if (sched_clock_irqtime) {
+		irqtime_account_process_tick(p, user_tick, 1);
+		return;
+	}
+
+	cputime = TICK_NSEC;
+	steal = steal_account_process_time(ULONG_MAX);
+
+	if (steal >= cputime)
+		return;
+
+	cputime -= steal;
+
+	if (user_tick)
+		account_user_time(p, cputime);
+	else if ((p != this_rq()->idle) || (irq_count() != HARDIRQ_OFFSET))
+		account_system_time(p, HARDIRQ_OFFSET, cputime);
+	else
+		account_idle_time(cputime);
+}
+
+/*
+ * Account multiple ticks of idle time.
+ * @ticks: number of stolen ticks
+ */
+void account_idle_ticks(unsigned long ticks)
+{
+	u64 cputime, steal;
+
+	if (sched_clock_irqtime) {
+		irqtime_account_idle_ticks(ticks);
+		return;
+	}
+
+	cputime = ticks * TICK_NSEC;
+	steal = steal_account_process_time(ULONG_MAX);
+
+	if (steal >= cputime)
+		return;
+
+	cputime -= steal;
+	account_idle_time(cputime);
+}
+
+/*
+ * Adjust tick based cputime random precision against scheduler runtime
+ * accounting.
+ *
+ * Tick based cputime accounting depend on random scheduling timeslices of a
+ * task to be interrupted or not by the timer.  Depending on these
+ * circumstances, the number of these interrupts may be over or
+ * under-optimistic, matching the real user and system cputime with a variable
+ * precision.
+ *
+ * Fix this by scaling these tick based values against the total runtime
+ * accounted by the CFS scheduler.
+ *
+ * This code provides the following guarantees:
+ *
+ *   stime + utime == rtime
+ *   stime_i+1 >= stime_i, utime_i+1 >= utime_i
+ *
+ * Assuming that rtime_i+1 >= rtime_i.
+ */
+void cputime_adjust(struct task_cputime *curr, struct prev_cputime *prev,
+		    u64 *ut, u64 *st)
+{
+	u64 rtime, stime, utime;
+	unsigned long flags;
+
+	/* Serialize concurrent callers such that we can honour our guarantees */
+	raw_spin_lock_irqsave(&prev->lock, flags);
+	rtime = curr->sum_exec_runtime;
+
+	/*
+	 * This is possible under two circumstances:
+	 *  - rtime isn't monotonic after all (a bug);
+	 *  - we got reordered by the lock.
+	 *
+	 * In both cases this acts as a filter such that the rest of the code
+	 * can assume it is monotonic regardless of anything else.
+	 */
+	if (prev->stime + prev->utime >= rtime)
+		goto out;
+
+	stime = curr->stime;
+	utime = curr->utime;
+
+	/*
+	 * If either stime or utime are 0, assume all runtime is userspace.
+	 * Once a task gets some ticks, the monotonicity code at 'update:'
+	 * will ensure things converge to the observed ratio.
+	 */
+	if (stime == 0) {
+		utime = rtime;
+		goto update;
+	}
+
+	if (utime == 0) {
+		stime = rtime;
+		goto update;
+	}
+
+	stime = mul_u64_u64_div_u64(stime, rtime, stime + utime);
+
+update:
+	/*
+	 * Make sure stime doesn't go backwards; this preserves monotonicity
+	 * for utime because rtime is monotonic.
+	 *
+	 *  utime_i+1 = rtime_i+1 - stime_i
+	 *            = rtime_i+1 - (rtime_i - utime_i)
+	 *            = (rtime_i+1 - rtime_i) + utime_i
+	 *            >= utime_i
+	 */
+	if (stime < prev->stime)
+		stime = prev->stime;
+	utime = rtime - stime;
+
+	/*
+	 * Make sure utime doesn't go backwards; this still preserves
+	 * monotonicity for stime, analogous argument to above.
+	 */
+	if (utime < prev->utime) {
+		utime = prev->utime;
+		stime = rtime - utime;
+	}
+
+	prev->stime = stime;
+	prev->utime = utime;
+out:
+	*ut = prev->utime;
+	*st = prev->stime;
+	raw_spin_unlock_irqrestore(&prev->lock, flags);
+}
+
+void task_cputime_adjusted(struct task_struct *p, u64 *ut, u64 *st)
+{
+	struct task_cputime cputime = {
+		.sum_exec_runtime = p->se.sum_exec_runtime,
+	};
+
+	if (task_cputime(p, &cputime.utime, &cputime.stime))
+		cputime.sum_exec_runtime = task_sched_runtime(p);
+	cputime_adjust(&cputime, &p->prev_cputime, ut, st);
+}
+EXPORT_SYMBOL_GPL(task_cputime_adjusted);
+
+void thread_group_cputime_adjusted(struct task_struct *p, u64 *ut, u64 *st)
+{
+	struct task_cputime cputime;
+
+	thread_group_cputime(p, &cputime);
+	cputime_adjust(&cputime, &p->signal->prev_cputime, ut, st);
+}
+#endif /* !CONFIG_VIRT_CPU_ACCOUNTING_NATIVE */
+
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
+static u64 vtime_delta(struct vtime *vtime)
+{
+	unsigned long long clock;
+
+	clock = sched_clock();
+	if (clock < vtime->starttime)
+		return 0;
+
+	return clock - vtime->starttime;
+}
+
+static u64 get_vtime_delta(struct vtime *vtime)
+{
+	u64 delta = vtime_delta(vtime);
+	u64 other;
+
+	/*
+	 * Unlike tick based timing, vtime based timing never has lost
+	 * ticks, and no need for steal time accounting to make up for
+	 * lost ticks. Vtime accounts a rounded version of actual
+	 * elapsed time. Limit account_other_time to prevent rounding
+	 * errors from causing elapsed vtime to go negative.
+	 */
+	other = account_other_time(delta);
+	WARN_ON_ONCE(vtime->state == VTIME_INACTIVE);
+	vtime->starttime += delta;
+
+	return delta - other;
+}
+
+static void vtime_account_system(struct task_struct *tsk,
+				 struct vtime *vtime)
+{
+	vtime->stime += get_vtime_delta(vtime);
+	if (vtime->stime >= TICK_NSEC) {
+		account_system_time(tsk, irq_count(), vtime->stime);
+		vtime->stime = 0;
+	}
+}
+
+static void vtime_account_guest(struct task_struct *tsk,
+				struct vtime *vtime)
+{
+	vtime->gtime += get_vtime_delta(vtime);
+	if (vtime->gtime >= TICK_NSEC) {
+		account_guest_time(tsk, vtime->gtime);
+		vtime->gtime = 0;
+	}
+}
+
+static void __vtime_account_kernel(struct task_struct *tsk,
+				   struct vtime *vtime)
+{
+	/* We might have scheduled out from guest path */
+	if (vtime->state == VTIME_GUEST)
+		vtime_account_guest(tsk, vtime);
+	else
+		vtime_account_system(tsk, vtime);
+}
+
+void vtime_account_kernel(struct task_struct *tsk)
+{
+	struct vtime *vtime = &tsk->vtime;
+
+	if (!vtime_delta(vtime))
+		return;
+
+	write_seqcount_begin(&vtime->seqcount);
+	__vtime_account_kernel(tsk, vtime);
+	write_seqcount_end(&vtime->seqcount);
+}
+
+void vtime_user_enter(struct task_struct *tsk)
+{
+	struct vtime *vtime = &tsk->vtime;
+
+	write_seqcount_begin(&vtime->seqcount);
+	vtime_account_system(tsk, vtime);
+	vtime->state = VTIME_USER;
+	write_seqcount_end(&vtime->seqcount);
+}
+
+void vtime_user_exit(struct task_struct *tsk)
+{
+	struct vtime *vtime = &tsk->vtime;
+
+	write_seqcount_begin(&vtime->seqcount);
+	vtime->utime += get_vtime_delta(vtime);
+	if (vtime->utime >= TICK_NSEC) {
+		account_user_time(tsk, vtime->utime);
+		vtime->utime = 0;
+	}
+	vtime->state = VTIME_SYS;
+	write_seqcount_end(&vtime->seqcount);
+}
+
+void vtime_guest_enter(struct task_struct *tsk)
+{
+	struct vtime *vtime = &tsk->vtime;
+	/*
+	 * The flags must be updated under the lock with
+	 * the vtime_starttime flush and update.
+	 * That enforces a right ordering and update sequence
+	 * synchronization against the reader (task_gtime())
+	 * that can thus safely catch up with a tickless delta.
+	 */
+	write_seqcount_begin(&vtime->seqcount);
+	vtime_account_system(tsk, vtime);
+	tsk->flags |= PF_VCPU;
+	vtime->state = VTIME_GUEST;
+	write_seqcount_end(&vtime->seqcount);
+}
+EXPORT_SYMBOL_GPL(vtime_guest_enter);
+
+void vtime_guest_exit(struct task_struct *tsk)
+{
+	struct vtime *vtime = &tsk->vtime;
+
+	write_seqcount_begin(&vtime->seqcount);
+	vtime_account_guest(tsk, vtime);
+	tsk->flags &= ~PF_VCPU;
+	vtime->state = VTIME_SYS;
+	write_seqcount_end(&vtime->seqcount);
+}
+EXPORT_SYMBOL_GPL(vtime_guest_exit);
+
+void vtime_account_idle(struct task_struct *tsk)
+{
+	account_idle_time(get_vtime_delta(&tsk->vtime));
+}
+
+void vtime_task_switch_generic(struct task_struct *prev)
+{
+	struct vtime *vtime = &prev->vtime;
+
+	write_seqcount_begin(&vtime->seqcount);
+	if (vtime->state == VTIME_IDLE)
+		vtime_account_idle(prev);
+	else
+		__vtime_account_kernel(prev, vtime);
+	vtime->state = VTIME_INACTIVE;
+	vtime->cpu = -1;
+	write_seqcount_end(&vtime->seqcount);
+
+	vtime = &current->vtime;
+
+	write_seqcount_begin(&vtime->seqcount);
+	if (is_idle_task(current))
+		vtime->state = VTIME_IDLE;
+	else if (current->flags & PF_VCPU)
+		vtime->state = VTIME_GUEST;
+	else
+		vtime->state = VTIME_SYS;
+	vtime->starttime = sched_clock();
+	vtime->cpu = smp_processor_id();
+	write_seqcount_end(&vtime->seqcount);
+}
+
+void vtime_init_idle(struct task_struct *t, int cpu)
+{
+	struct vtime *vtime = &t->vtime;
+	unsigned long flags;
+
+	local_irq_save(flags);
+	write_seqcount_begin(&vtime->seqcount);
+	vtime->state = VTIME_IDLE;
+	vtime->starttime = sched_clock();
+	vtime->cpu = cpu;
+	write_seqcount_end(&vtime->seqcount);
+	local_irq_restore(flags);
+}
+
+u64 task_gtime(struct task_struct *t)
+{
+	struct vtime *vtime = &t->vtime;
+	unsigned int seq;
+	u64 gtime;
+
+	if (!vtime_accounting_enabled())
+		return t->gtime;
+
+	do {
+		seq = read_seqcount_begin(&vtime->seqcount);
+
+		gtime = t->gtime;
+		if (vtime->state == VTIME_GUEST)
+			gtime += vtime->gtime + vtime_delta(vtime);
+
+	} while (read_seqcount_retry(&vtime->seqcount, seq));
+
+	return gtime;
+}
+
+/*
+ * Fetch cputime raw values from fields of task_struct and
+ * add up the pending nohz execution time since the last
+ * cputime snapshot.
+ */
+bool task_cputime(struct task_struct *t, u64 *utime, u64 *stime)
+{
+	struct vtime *vtime = &t->vtime;
+	unsigned int seq;
+	u64 delta;
+	int ret;
+
+	if (!vtime_accounting_enabled()) {
+		*utime = t->utime;
+		*stime = t->stime;
+		return false;
+	}
+
+	do {
+		ret = false;
+		seq = read_seqcount_begin(&vtime->seqcount);
+
+		*utime = t->utime;
+		*stime = t->stime;
+
+		/* Task is sleeping or idle, nothing to add */
+		if (vtime->state < VTIME_SYS)
+			continue;
+
+		ret = true;
+		delta = vtime_delta(vtime);
+
+		/*
+		 * Task runs either in user (including guest) or kernel space,
+		 * add pending nohz time to the right place.
+		 */
+		if (vtime->state == VTIME_SYS)
+			*stime += vtime->stime + delta;
+		else
+			*utime += vtime->utime + delta;
+	} while (read_seqcount_retry(&vtime->seqcount, seq));
+
+	return ret;
+}
+
+static int vtime_state_fetch(struct vtime *vtime, int cpu)
+{
+	int state = READ_ONCE(vtime->state);
+
+	/*
+	 * We raced against a context switch, fetch the
+	 * kcpustat task again.
+	 */
+	if (vtime->cpu != cpu && vtime->cpu != -1)
+		return -EAGAIN;
+
+	/*
+	 * Two possible things here:
+	 * 1) We are seeing the scheduling out task (prev) or any past one.
+	 * 2) We are seeing the scheduling in task (next) but it hasn't
+	 *    passed though vtime_task_switch() yet so the pending
+	 *    cputime of the prev task may not be flushed yet.
+	 *
+	 * Case 1) is ok but 2) is not. So wait for a safe VTIME state.
+	 */
+	if (state == VTIME_INACTIVE)
+		return -EAGAIN;
+
+	return state;
+}
+
+static u64 kcpustat_user_vtime(struct vtime *vtime)
+{
+	if (vtime->state == VTIME_USER)
+		return vtime->utime + vtime_delta(vtime);
+	else if (vtime->state == VTIME_GUEST)
+		return vtime->gtime + vtime_delta(vtime);
+	return 0;
+}
+
+static int kcpustat_field_vtime(u64 *cpustat,
+				struct task_struct *tsk,
+				enum cpu_usage_stat usage,
+				int cpu, u64 *val)
+{
+	struct vtime *vtime = &tsk->vtime;
+	unsigned int seq;
+
+	do {
+		int state;
+
+		seq = read_seqcount_begin(&vtime->seqcount);
+
+		state = vtime_state_fetch(vtime, cpu);
+		if (state < 0)
+			return state;
+
+		*val = cpustat[usage];
+
+		/*
+		 * Nice VS unnice cputime accounting may be inaccurate if
+		 * the nice value has changed since the last vtime update.
+		 * But proper fix would involve interrupting target on nice
+		 * updates which is a no go on nohz_full (although the scheduler
+		 * may still interrupt the target if rescheduling is needed...)
+		 */
+		switch (usage) {
+		case CPUTIME_SYSTEM:
+			if (state == VTIME_SYS)
+				*val += vtime->stime + vtime_delta(vtime);
+			break;
+		case CPUTIME_USER:
+			if (task_nice(tsk) <= 0)
+				*val += kcpustat_user_vtime(vtime);
+			break;
+		case CPUTIME_NICE:
+			if (task_nice(tsk) > 0)
+				*val += kcpustat_user_vtime(vtime);
+			break;
+		case CPUTIME_GUEST:
+			if (state == VTIME_GUEST && task_nice(tsk) <= 0)
+				*val += vtime->gtime + vtime_delta(vtime);
+			break;
+		case CPUTIME_GUEST_NICE:
+			if (state == VTIME_GUEST && task_nice(tsk) > 0)
+				*val += vtime->gtime + vtime_delta(vtime);
+			break;
+		default:
+			break;
+		}
+	} while (read_seqcount_retry(&vtime->seqcount, seq));
+
+	return 0;
+}
+
+u64 kcpustat_field(struct kernel_cpustat *kcpustat,
+		   enum cpu_usage_stat usage, int cpu)
+{
+	u64 *cpustat = kcpustat->cpustat;
+	u64 val = cpustat[usage];
+	struct rq *rq;
+	int err;
+
+	if (!vtime_accounting_enabled_cpu(cpu))
+		return val;
+
+	rq = cpu_rq(cpu);
+
+	for (;;) {
+		struct task_struct *curr;
+
+		rcu_read_lock();
+		curr = rcu_dereference(rq->curr);
+		if (WARN_ON_ONCE(!curr)) {
+			rcu_read_unlock();
+			return cpustat[usage];
+		}
+
+		err = kcpustat_field_vtime(cpustat, curr, usage, cpu, &val);
+		rcu_read_unlock();
+
+		if (!err)
+			return val;
+
+		cpu_relax();
+	}
+}
+EXPORT_SYMBOL_GPL(kcpustat_field);
+
+static int kcpustat_cpu_fetch_vtime(struct kernel_cpustat *dst,
+				    const struct kernel_cpustat *src,
+				    struct task_struct *tsk, int cpu)
+{
+	struct vtime *vtime = &tsk->vtime;
+	unsigned int seq;
+
+	do {
+		u64 *cpustat;
+		u64 delta;
+		int state;
+
+		seq = read_seqcount_begin(&vtime->seqcount);
+
+		state = vtime_state_fetch(vtime, cpu);
+		if (state < 0)
+			return state;
+
+		*dst = *src;
+		cpustat = dst->cpustat;
+
+		/* Task is sleeping, dead or idle, nothing to add */
+		if (state < VTIME_SYS)
+			continue;
+
+		delta = vtime_delta(vtime);
+
+		/*
+		 * Task runs either in user (including guest) or kernel space,
+		 * add pending nohz time to the right place.
+		 */
+		if (state == VTIME_SYS) {
+			cpustat[CPUTIME_SYSTEM] += vtime->stime + delta;
+		} else if (state == VTIME_USER) {
+			if (task_nice(tsk) > 0)
+				cpustat[CPUTIME_NICE] += vtime->utime + delta;
+			else
+				cpustat[CPUTIME_USER] += vtime->utime + delta;
+		} else {
+			WARN_ON_ONCE(state != VTIME_GUEST);
+			if (task_nice(tsk) > 0) {
+				cpustat[CPUTIME_GUEST_NICE] += vtime->gtime + delta;
+				cpustat[CPUTIME_NICE] += vtime->gtime + delta;
+			} else {
+				cpustat[CPUTIME_GUEST] += vtime->gtime + delta;
+				cpustat[CPUTIME_USER] += vtime->gtime + delta;
+			}
+		}
+	} while (read_seqcount_retry(&vtime->seqcount, seq));
+
+	return 0;
+}
+
+void kcpustat_cpu_fetch(struct kernel_cpustat *dst, int cpu)
+{
+	const struct kernel_cpustat *src = &kcpustat_cpu(cpu);
+	struct rq *rq;
+	int err;
+
+	if (!vtime_accounting_enabled_cpu(cpu)) {
+		*dst = *src;
+		return;
+	}
+
+	rq = cpu_rq(cpu);
+
+	for (;;) {
+		struct task_struct *curr;
+
+		rcu_read_lock();
+		curr = rcu_dereference(rq->curr);
+		if (WARN_ON_ONCE(!curr)) {
+			rcu_read_unlock();
+			*dst = *src;
+			return;
+		}
+
+		err = kcpustat_cpu_fetch_vtime(dst, src, curr, cpu);
+		rcu_read_unlock();
+
+		if (!err)
+			return;
+
+		cpu_relax();
+	}
+}
+EXPORT_SYMBOL_GPL(kcpustat_cpu_fetch);
+
+#endif /* CONFIG_VIRT_CPU_ACCOUNTING_GEN */