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 #include <asm/qspinlock.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 bool xen_pvspin = true;
  25
  26 static void xen_qlock_kick(int cpu)
  27 {
  28         int irq = per_cpu(lock_kicker_irq, cpu);
  29
  30         /* Don't kick if the target's kicker interrupt is not initialized. */
  31         if (irq == -1)
  32                 return;
  33
  34         xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
  35 }
  36
  37 /*
  38  * Halt the current CPU & release it back to the host
  39  */
  40 static void xen_qlock_wait(u8 *byte, u8 val)
  41 {
  42         int irq = __this_cpu_read(lock_kicker_irq);
  43
  44         /* If kicker interrupts not initialized yet, just spin */
  45         if (irq == -1)
  46                 return;
  47
  48         /* clear pending */
  49         xen_clear_irq_pending(irq);
  50         barrier();
  51
  52         /*
  53          * We check the byte value after clearing pending IRQ to make sure
  54          * that we won't miss a wakeup event because of the clearing.
  55          *
  56          * The sync_clear_bit() call in xen_clear_irq_pending() is atomic.
  57          * So it is effectively a memory barrier for x86.
  58          */
  59         if (READ_ONCE(*byte) != val)
  60                 return;
  61
  62         /*
  63          * If an interrupt happens here, it will leave the wakeup irq
  64          * pending, which will cause xen_poll_irq() to return
  65          * immediately.
  66          */
  67
  68         /* Block until irq becomes pending (or perhaps a spurious wakeup) */
  69         xen_poll_irq(irq);
  70 }
  71
  72 static irqreturn_t dummy_handler(int irq, void *dev_id)
  73 {
  74         BUG();
  75         return IRQ_HANDLED;
  76 }
  77
  78 void xen_init_lock_cpu(int cpu)
  79 {
  80         int irq;
  81         char *name;
  82
  83         if (!xen_pvspin) {
  84                 if (cpu == 0)
  85                         static_branch_disable(&virt_spin_lock_key);
  86                 return;
  87         }
  88
  89         WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
  90              cpu, per_cpu(lock_kicker_irq, cpu));
  91
  92         name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
  93         irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
  94                                      cpu,
  95                                      dummy_handler,
  96                                      IRQF_PERCPU|IRQF_NOBALANCING,
  97                                      name,
  98                                      NULL);
  99
 100         if (irq >= 0) {
 101                 disable_irq(irq); /* make sure it's never delivered */
 102                 per_cpu(lock_kicker_irq, cpu) = irq;
 103                 per_cpu(irq_name, cpu) = name;
 104         }
 105
 106         printk("cpu %d spinlock event irq %d\n", cpu, irq);
 107 }
 108
 109 void xen_uninit_lock_cpu(int cpu)
 110 {
 111         if (!xen_pvspin)
 112                 return;
 113
 114         unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
 115         per_cpu(lock_kicker_irq, cpu) = -1;
 116         kfree(per_cpu(irq_name, cpu));
 117         per_cpu(irq_name, cpu) = NULL;
 118 }
 119
 120 PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen);
 121
 122 /*
 123  * Our init of PV spinlocks is split in two init functions due to us
 124  * using paravirt patching and jump labels patching and having to do
 125  * all of this before SMP code is invoked.
 126  *
 127  * The paravirt patching needs to be done _before_ the alternative asm code
 128  * is started, otherwise we would not patch the core kernel code.
 129  */
 130 void __init xen_init_spinlocks(void)
 131 {
 132
 133         if (!xen_pvspin) {
 134                 printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
 135                 return;
 136         }
 137         printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
 138
 139         __pv_init_lock_hash();
 140         pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
 141         pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
 142         pv_lock_ops.wait = xen_qlock_wait;
 143         pv_lock_ops.kick = xen_qlock_kick;
 144         pv_lock_ops.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen);
 145 }
 146
 147 static __init int xen_parse_nopvspin(char *arg)
 148 {
 149         xen_pvspin = false;
 150         return 0;
 151 }
 152 early_param("xen_nopvspin", xen_parse_nopvspin);
 153