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 #include <asm/qspinlock.h>
  27
  28 static void xen_qlock_kick(int cpu)
  29 {
  30         int irq = per_cpu(lock_kicker_irq, cpu);
  31
  32         /* Don't kick if the target's kicker interrupt is not initialized. */
  33         if (irq == -1)
  34                 return;
  35
  36         xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
  37 }
  38
  39 /*
  40  * Halt the current CPU & release it back to the host
  41  */
  42 static void xen_qlock_wait(u8 *byte, u8 val)
  43 {
  44         int irq = __this_cpu_read(lock_kicker_irq);
  45
  46         /* If kicker interrupts not initialized yet, just spin */
  47         if (irq == -1)
  48                 return;
  49
  50         /* clear pending */
  51         xen_clear_irq_pending(irq);
  52         barrier();
  53
  54         /*
  55          * We check the byte value after clearing pending IRQ to make sure
  56          * that we won't miss a wakeup event because of the clearing.
  57          *
  58          * The sync_clear_bit() call in xen_clear_irq_pending() is atomic.
  59          * So it is effectively a memory barrier for x86.
  60          */
  61         if (READ_ONCE(*byte) != val)
  62                 return;
  63
  64         /*
  65          * If an interrupt happens here, it will leave the wakeup irq
  66          * pending, which will cause xen_poll_irq() to return
  67          * immediately.
  68          */
  69
  70         /* Block until irq becomes pending (or perhaps a spurious wakeup) */
  71         xen_poll_irq(irq);
  72 }
  73
  74 static irqreturn_t dummy_handler(int irq, void *dev_id)
  75 {
  76         BUG();
  77         return IRQ_HANDLED;
  78 }
  79
  80 void xen_init_lock_cpu(int cpu)
  81 {
  82         int irq;
  83         char *name;
  84
  85         if (!xen_pvspin) {
  86                 if (cpu == 0)
  87                         static_branch_disable(&virt_spin_lock_key);
  88                 return;
  89         }
  90
  91         WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
  92              cpu, per_cpu(lock_kicker_irq, cpu));
  93
  94         name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
  95         irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
  96                                      cpu,
  97                                      dummy_handler,
  98                                      IRQF_PERCPU|IRQF_NOBALANCING,
  99                                      name,
 100                                      NULL);
 101
 102         if (irq >= 0) {
 103                 disable_irq(irq); /* make sure it's never delivered */
 104                 per_cpu(lock_kicker_irq, cpu) = irq;
 105                 per_cpu(irq_name, cpu) = name;
 106         }
 107
 108         printk("cpu %d spinlock event irq %d\n", cpu, irq);
 109 }
 110
 111 void xen_uninit_lock_cpu(int cpu)
 112 {
 113         if (!xen_pvspin)
 114                 return;
 115
 116         unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
 117         per_cpu(lock_kicker_irq, cpu) = -1;
 118         kfree(per_cpu(irq_name, cpu));
 119         per_cpu(irq_name, cpu) = NULL;
 120 }
 121
 122 PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen);
 123
 124 /*
 125  * Our init of PV spinlocks is split in two init functions due to us
 126  * using paravirt patching and jump labels patching and having to do
 127  * all of this before SMP code is invoked.
 128  *
 129  * The paravirt patching needs to be done _before_ the alternative asm code
 130  * is started, otherwise we would not patch the core kernel code.
 131  */
 132 void __init xen_init_spinlocks(void)
 133 {
 134
 135         if (!xen_pvspin) {
 136                 printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
 137                 return;
 138         }
 139         printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
 140
 141         __pv_init_lock_hash();
 142         pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
 143         pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
 144         pv_lock_ops.wait = xen_qlock_wait;
 145         pv_lock_ops.kick = xen_qlock_kick;
 146         pv_lock_ops.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen);
 147 }
 148
 149 static __init int xen_parse_nopvspin(char *arg)
 150 {
 151         xen_pvspin = false;
 152         return 0;
 153 }
 154 early_param("xen_nopvspin", xen_parse_nopvspin);
 155