LXR linux/arch/x86/xen/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);
  21static bool xen_pvspin = true;
  22
  23static void xen_qlock_kick(int cpu)
  24{
  25        int irq = per_cpu(lock_kicker_irq, cpu);
  26
  27        /* Don't kick if the target's kicker interrupt is not initialized. */
  28        if (irq == -1)
  29                return;
  30
  31        xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
  32}
  33
  34/*
  35 * Halt the current CPU & release it back to the host
  36 */
  37static void xen_qlock_wait(u8 *byte, u8 val)
  38{
  39        int irq = __this_cpu_read(lock_kicker_irq);
  40        atomic_t *nest_cnt = this_cpu_ptr(&xen_qlock_wait_nest);
  41
  42        /* If kicker interrupts not initialized yet, just spin */
  43        if (irq == -1 || in_nmi())
  44                return;
  45
  46        /* Detect reentry. */
  47        atomic_inc(nest_cnt);
  48
  49        /* If irq pending already and no nested call clear it. */
  50        if (atomic_read(nest_cnt) == 1 && xen_test_irq_pending(irq)) {
  51                xen_clear_irq_pending(irq);
  52        } else if (READ_ONCE(*byte) == val) {
  53                /* Block until irq becomes pending (or a spurious wakeup) */
  54                xen_poll_irq(irq);
  55        }
  56
  57        atomic_dec(nest_cnt);
  58}
  59
  60static irqreturn_t dummy_handler(int irq, void *dev_id)
  61{
  62        BUG();
  63        return IRQ_HANDLED;
  64}
  65
  66void xen_init_lock_cpu(int cpu)
  67{
  68        int irq;
  69        char *name;
  70
  71        if (!xen_pvspin) {
  72                if (cpu == 0)
  73                        static_branch_disable(&virt_spin_lock_key);
  74                return;
  75        }
  76
  77        WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
  78             cpu, per_cpu(lock_kicker_irq, cpu));
  79
  80        name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
  81        irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
  82                                     cpu,
  83                                     dummy_handler,
  84                                     IRQF_PERCPU|IRQF_NOBALANCING,
  85                                     name,
  86                                     NULL);
  87
  88        if (irq >= 0) {
  89                disable_irq(irq); /* make sure it's never delivered */
  90                per_cpu(lock_kicker_irq, cpu) = irq;
  91                per_cpu(irq_name, cpu) = name;
  92        }
  93
  94        printk("cpu %d spinlock event irq %d\n", cpu, irq);
  95}
  96
  97void xen_uninit_lock_cpu(int cpu)
  98{
  99        if (!xen_pvspin)
 100                return;
 101
 102        unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
 103        per_cpu(lock_kicker_irq, cpu) = -1;
 104        kfree(per_cpu(irq_name, cpu));
 105        per_cpu(irq_name, cpu) = NULL;
 106}
 107
 108PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen);
 109
 110/*
 111 * Our init of PV spinlocks is split in two init functions due to us
 112 * using paravirt patching and jump labels patching and having to do
 113 * all of this before SMP code is invoked.
 114 *
 115 * The paravirt patching needs to be done _before_ the alternative asm code
 116 * is started, otherwise we would not patch the core kernel code.
 117 */
 118void __init xen_init_spinlocks(void)
 119{
 120
 121        /*  Don't need to use pvqspinlock code if there is only 1 vCPU. */
 122        if (num_possible_cpus() == 1)
 123                xen_pvspin = false;
 124
 125        if (!xen_pvspin) {
 126                printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
 127                return;
 128        }
 129        printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
 130
 131        __pv_init_lock_hash();
 132        pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
 133        pv_ops.lock.queued_spin_unlock =
 134                PV_CALLEE_SAVE(__pv_queued_spin_unlock);
 135        pv_ops.lock.wait = xen_qlock_wait;
 136        pv_ops.lock.kick = xen_qlock_kick;
 137        pv_ops.lock.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen);
 138}
 139
 140static __init int xen_parse_nopvspin(char *arg)
 141{
 142        xen_pvspin = false;
 143        return 0;
 144}
 145early_param("xen_nopvspin", xen_parse_nopvspin);
 146
 147