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
  13 #include <asm/paravirt.h>
  14
  15 #include <xen/interface/xen.h>
  16 #include <xen/events.h>
  17
  18 #include "xen-ops.h"
  19 #include "debugfs.h"
  20
  21 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
  22 static DEFINE_PER_CPU(char *, irq_name);
  23 static bool xen_pvspin = true;
  24
  25 #include <asm/qspinlock.h>
  26
  27 static void xen_qlock_kick(int cpu)
  28 {
  29         int irq = per_cpu(lock_kicker_irq, cpu);
  30
  31         /* Don't kick if the target's kicker interrupt is not initialized. */
  32         if (irq == -1)
  33                 return;
  34
  35         xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
  36 }
  37
  38 /*
  39  * Halt the current CPU & release it back to the host
  40  */
  41 static void xen_qlock_wait(u8 *byte, u8 val)
  42 {
  43         int irq = __this_cpu_read(lock_kicker_irq);
  44
  45         /* If kicker interrupts not initialized yet, just spin */
  46         if (irq == -1)
  47                 return;
  48
  49         /* clear pending */
  50         xen_clear_irq_pending(irq);
  51         barrier();
  52
  53         /*
  54          * We check the byte value after clearing pending IRQ to make sure
  55          * that we won't miss a wakeup event because of the clearing.
  56          *
  57          * The sync_clear_bit() call in xen_clear_irq_pending() is atomic.
  58          * So it is effectively a memory barrier for x86.
  59          */
  60         if (READ_ONCE(*byte) != val)
  61                 return;
  62
  63         /*
  64          * If an interrupt happens here, it will leave the wakeup irq
  65          * pending, which will cause xen_poll_irq() to return
  66          * immediately.
  67          */
  68
  69         /* Block until irq becomes pending (or perhaps a spurious wakeup) */
  70         xen_poll_irq(irq);
  71 }
  72
  73 static irqreturn_t dummy_handler(int irq, void *dev_id)
  74 {
  75         BUG();
  76         return IRQ_HANDLED;
  77 }
  78
  79 void xen_init_lock_cpu(int cpu)
  80 {
  81         int irq;
  82         char *name;
  83
  84         if (!xen_pvspin)
  85                 return;
  86
  87         WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
  88              cpu, per_cpu(lock_kicker_irq, cpu));
  89
  90         name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
  91         irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
  92                                      cpu,
  93                                      dummy_handler,
  94                                      IRQF_PERCPU|IRQF_NOBALANCING,
  95                                      name,
  96                                      NULL);
  97
  98         if (irq >= 0) {
  99                 disable_irq(irq); /* make sure it's never delivered */
 100                 per_cpu(lock_kicker_irq, cpu) = irq;
 101                 per_cpu(irq_name, cpu) = name;
 102         }
 103
 104         printk("cpu %d spinlock event irq %d\n", cpu, irq);
 105 }
 106
 107 void xen_uninit_lock_cpu(int cpu)
 108 {
 109         if (!xen_pvspin)
 110                 return;
 111
 112         unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
 113         per_cpu(lock_kicker_irq, cpu) = -1;
 114         kfree(per_cpu(irq_name, cpu));
 115         per_cpu(irq_name, cpu) = NULL;
 116 }
 117
 118 PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen);
 119
 120 /*
 121  * Our init of PV spinlocks is split in two init functions due to us
 122  * using paravirt patching and jump labels patching and having to do
 123  * all of this before SMP code is invoked.
 124  *
 125  * The paravirt patching needs to be done _before_ the alternative asm code
 126  * is started, otherwise we would not patch the core kernel code.
 127  */
 128 void __init xen_init_spinlocks(void)
 129 {
 130
 131         if (!xen_pvspin) {
 132                 printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
 133                 return;
 134         }
 135         printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
 136
 137         __pv_init_lock_hash();
 138         pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
 139         pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
 140         pv_lock_ops.wait = xen_qlock_wait;
 141         pv_lock_ops.kick = xen_qlock_kick;
 142         pv_lock_ops.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen);
 143 }
 144
 145 static __init int xen_parse_nopvspin(char *arg)
 146 {
 147         xen_pvspin = false;
 148         return 0;
 149 }
 150 early_param("xen_nopvspin", xen_parse_nopvspin);
 151