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
  18 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
  19 static DEFINE_PER_CPU(char *, irq_name);
  20 static DEFINE_PER_CPU(atomic_t, xen_qlock_wait_nest);
  21 static bool xen_pvspin = true;
  22
  23 static 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  */
  37 static 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
  60 static irqreturn_t dummy_handler(int irq, void *dev_id)
  61 {
  62         BUG();
  63         return IRQ_HANDLED;
  64 }
  65
  66 void xen_init_lock_cpu(int cpu)
  67 {
  68         int irq;
  69         char *name;
  70
  71         if (!xen_pvspin)
  72                 return;
  73
  74         WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
  75              cpu, per_cpu(lock_kicker_irq, cpu));
  76
  77         name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
  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                 per_cpu(irq_name, cpu) = name;
  89         }
  90
  91         printk("cpu %d spinlock event irq %d\n", cpu, irq);
  92 }
  93
  94 void xen_uninit_lock_cpu(int cpu)
  95 {
  96         int irq;
  97
  98         if (!xen_pvspin)
  99                 return;
 100
 101         /*
 102          * When booting the kernel with 'mitigations=auto,nosmt', the secondary
 103          * CPUs are not activated, and lock_kicker_irq is not initialized.
 104          */
 105         irq = per_cpu(lock_kicker_irq, cpu);
 106         if (irq == -1)
 107                 return;
 108
 109         unbind_from_irqhandler(irq, NULL);
 110         per_cpu(lock_kicker_irq, cpu) = -1;
 111         kfree(per_cpu(irq_name, cpu));
 112         per_cpu(irq_name, cpu) = NULL;
 113 }
 114
 115 PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen);
 116
 117 /*
 118  * Our init of PV spinlocks is split in two init functions due to us
 119  * using paravirt patching and jump labels patching and having to do
 120  * all of this before SMP code is invoked.
 121  *
 122  * The paravirt patching needs to be done _before_ the alternative asm code
 123  * is started, otherwise we would not patch the core kernel code.
 124  */
 125 void __init xen_init_spinlocks(void)
 126 {
 127         /*  Don't need to use pvqspinlock code if there is only 1 vCPU. */
 128         if (num_possible_cpus() == 1 || nopvspin)
 129                 xen_pvspin = false;
 130
 131         if (!xen_pvspin) {
 132                 printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
 133                 static_branch_disable(&virt_spin_lock_key);
 134                 return;
 135         }
 136         printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
 137
 138         __pv_init_lock_hash();
 139         pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
 140         pv_ops.lock.queued_spin_unlock =
 141                 PV_CALLEE_SAVE(__pv_queued_spin_unlock);
 142         pv_ops.lock.wait = xen_qlock_wait;
 143         pv_ops.lock.kick = xen_qlock_kick;
 144         pv_ops.lock.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen);
 145 }
 146
 147 static __init int xen_parse_nopvspin(char *arg)
 148 {
 149         pr_notice("\"xen_nopvspin\" is deprecated, please use \"nopvspin\" instead\n");
 150         xen_pvspin = false;
 151         return 0;
 152 }
 153 early_param("xen_nopvspin", xen_parse_nopvspin);
 154