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_stat.h>
   7 #include <linux/spinlock.h>
   8 #include <linux/debugfs.h>
   9 #include <linux/log2.h>
  10 #include <linux/gfp.h>
  11 #include <linux/slab.h>
  12 #include <linux/atomic.h>
  13
  14 #include <asm/paravirt.h>
  15
  16 #include <xen/interface/xen.h>
  17 #include <xen/events.h>
  18
  19 #include "xen-ops.h"
  20 #include "debugfs.h"
  21
  22 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
  23 static DEFINE_PER_CPU(char *, irq_name);
  24 static DEFINE_PER_CPU(atomic_t, xen_qlock_wait_nest);
  25 static bool xen_pvspin = true;
  26
  27 #include <asm/qspinlock.h>
  28
  29 static void xen_qlock_kick(int cpu)
  30 {
  31         int irq = per_cpu(lock_kicker_irq, cpu);
  32
  33         /* Don't kick if the target's kicker interrupt is not initialized. */
  34         if (irq == -1)
  35                 return;
  36
  37         xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
  38 }
  39
  40 /*
  41  * Halt the current CPU & release it back to the host
  42  */
  43 static void xen_qlock_wait(u8 *byte, u8 val)
  44 {
  45         int irq = __this_cpu_read(lock_kicker_irq);
  46         atomic_t *nest_cnt = this_cpu_ptr(&xen_qlock_wait_nest);
  47
  48         /* If kicker interrupts not initialized yet, just spin */
  49         if (irq == -1 || in_nmi())
  50                 return;
  51
  52         /* Detect reentry. */
  53         atomic_inc(nest_cnt);
  54
  55         /* If irq pending already and no nested call clear it. */
  56         if (atomic_read(nest_cnt) == 1 && xen_test_irq_pending(irq)) {
  57                 xen_clear_irq_pending(irq);
  58         } else if (READ_ONCE(*byte) == val) {
  59                 /* Block until irq becomes pending (or a spurious wakeup) */
  60                 xen_poll_irq(irq);
  61         }
  62
  63         atomic_dec(nest_cnt);
  64 }
  65
  66 static irqreturn_t dummy_handler(int irq, void *dev_id)
  67 {
  68         BUG();
  69         return IRQ_HANDLED;
  70 }
  71
  72 void xen_init_lock_cpu(int cpu)
  73 {
  74         int irq;
  75         char *name;
  76
  77         if (!xen_pvspin)
  78                 return;
  79
  80         WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
  81              cpu, per_cpu(lock_kicker_irq, cpu));
  82
  83         name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
  84         irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
  85                                      cpu,
  86                                      dummy_handler,
  87                                      IRQF_PERCPU|IRQF_NOBALANCING,
  88                                      name,
  89                                      NULL);
  90
  91         if (irq >= 0) {
  92                 disable_irq(irq); /* make sure it's never delivered */
  93                 per_cpu(lock_kicker_irq, cpu) = irq;
  94                 per_cpu(irq_name, cpu) = name;
  95         }
  96
  97         printk("cpu %d spinlock event irq %d\n", cpu, irq);
  98 }
  99
 100 void xen_uninit_lock_cpu(int cpu)
 101 {
 102         int irq;
 103
 104         if (!xen_pvspin)
 105                 return;
 106
 107         /*
 108          * When booting the kernel with 'mitigations=auto,nosmt', the secondary
 109          * CPUs are not activated, and lock_kicker_irq is not initialized.
 110          */
 111         irq = per_cpu(lock_kicker_irq, cpu);
 112         if (irq == -1)
 113                 return;
 114
 115         unbind_from_irqhandler(irq, NULL);
 116         per_cpu(lock_kicker_irq, cpu) = -1;
 117         kfree(per_cpu(irq_name, cpu));
 118         per_cpu(irq_name, cpu) = NULL;
 119 }
 120
 121 PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen);
 122
 123 /*
 124  * Our init of PV spinlocks is split in two init functions due to us
 125  * using paravirt patching and jump labels patching and having to do
 126  * all of this before SMP code is invoked.
 127  *
 128  * The paravirt patching needs to be done _before_ the alternative asm code
 129  * is started, otherwise we would not patch the core kernel code.
 130  */
 131 void __init xen_init_spinlocks(void)
 132 {
 133
 134         if (!xen_pvspin) {
 135                 printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
 136                 return;
 137         }
 138         printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
 139
 140         __pv_init_lock_hash();
 141         pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
 142         pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
 143         pv_lock_ops.wait = xen_qlock_wait;
 144         pv_lock_ops.kick = xen_qlock_kick;
 145         pv_lock_ops.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen);
 146 }
 147
 148 static __init int xen_parse_nopvspin(char *arg)
 149 {
 150         xen_pvspin = false;
 151         return 0;
 152 }
 153 early_param("xen_nopvspin", xen_parse_nopvspin);
 154