spinlock.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Split spinlock implementation out into its own file, so it can be
  4 * compiled in a FTRACE-compatible way.
  5 */
  6#include <linux/kernel.h>
  7#include <linux/spinlock.h>
  8#include <linux/slab.h>
  9#include <linux/atomic.h>
 10
 11#include <asm/paravirt.h>
 12#include <asm/qspinlock.h>
 13
 14#include <xen/events.h>
 15
 16#include "xen-ops.h"
 17
 18static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
 19static DEFINE_PER_CPU(char *, irq_name);
 20static DEFINE_PER_CPU(atomic_t, xen_qlock_wait_nest);
 21
 22static void xen_qlock_kick(int cpu)
 23{
 24	int irq = per_cpu(lock_kicker_irq, cpu);
 25
 26	/* Don't kick if the target's kicker interrupt is not initialized. */
 27	if (irq == -1)
 28		return;
 29
 30	xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
 31}
 32
 33/*
 34 * Halt the current CPU & release it back to the host
 35 */
 36static void xen_qlock_wait(u8 *byte, u8 val)
 37{
 38	int irq = __this_cpu_read(lock_kicker_irq);
 39	atomic_t *nest_cnt = this_cpu_ptr(&xen_qlock_wait_nest);
 40
 41	/* If kicker interrupts not initialized yet, just spin */
 42	if (irq == -1 || in_nmi())
 43		return;
 44
 45	/* Detect reentry. */
 46	atomic_inc(nest_cnt);
 47
 48	/* If irq pending already and no nested call clear it. */
 49	if (atomic_read(nest_cnt) == 1 && xen_test_irq_pending(irq)) {
 50		xen_clear_irq_pending(irq);
 51	} else if (READ_ONCE(*byte) == val) {
 52		/* Block until irq becomes pending (or a spurious wakeup) */
 53		xen_poll_irq(irq);
 54	}
 55
 56	atomic_dec(nest_cnt);
 57}
 58
 59static irqreturn_t dummy_handler(int irq, void *dev_id)
 60{
 61	BUG();
 62	return IRQ_HANDLED;
 63}
 64
 65void xen_init_lock_cpu(int cpu)
 66{
 67	int irq;
 68	char *name;
 69
 70	if (nopvspin)
 71		return;
 72
 73	WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
 74	     cpu, per_cpu(lock_kicker_irq, cpu));
 75
 76	name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
 77	per_cpu(irq_name, cpu) = name;
 78	irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
 79				     cpu,
 80				     dummy_handler,
 81				     IRQF_PERCPU|IRQF_NOBALANCING,
 82				     name,
 83				     NULL);
 84
 85	if (irq >= 0) {
 86		disable_irq(irq); /* make sure it's never delivered */
 87		per_cpu(lock_kicker_irq, cpu) = irq;
 88	}
 89
 90	printk("cpu %d spinlock event irq %d\n", cpu, irq);
 91}
 92
 93void xen_uninit_lock_cpu(int cpu)
 94{
 95	int irq;
 96
 97	if (nopvspin)
 98		return;
 99
100	kfree(per_cpu(irq_name, cpu));
101	per_cpu(irq_name, cpu) = NULL;
102	/*
103	 * When booting the kernel with 'mitigations=auto,nosmt', the secondary
104	 * CPUs are not activated, and lock_kicker_irq is not initialized.
105	 */
106	irq = per_cpu(lock_kicker_irq, cpu);
107	if (irq == -1)
108		return;
109
110	unbind_from_irqhandler(irq, NULL);
111	per_cpu(lock_kicker_irq, cpu) = -1;
112}
113
114PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen);
115
116/*
117 * Our init of PV spinlocks is split in two init functions due to us
118 * using paravirt patching and jump labels patching and having to do
119 * all of this before SMP code is invoked.
120 *
121 * The paravirt patching needs to be done _before_ the alternative asm code
122 * is started, otherwise we would not patch the core kernel code.
123 */
124void __init xen_init_spinlocks(void)
125{
126	/*  Don't need to use pvqspinlock code if there is only 1 vCPU. */
127	if (num_possible_cpus() == 1)
128		nopvspin = true;
129
130	if (nopvspin) {
131		printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
132		static_branch_disable(&virt_spin_lock_key);
133		return;
134	}
135	printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
136
137	__pv_init_lock_hash();
138	pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
139	pv_ops.lock.queued_spin_unlock =
140		PV_CALLEE_SAVE(__pv_queued_spin_unlock);
141	pv_ops.lock.wait = xen_qlock_wait;
142	pv_ops.lock.kick = xen_qlock_kick;
143	pv_ops.lock.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen);
144}