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         unsigned long flags;
  43         int irq = __this_cpu_read(lock_kicker_irq);
  44
  45         /* If kicker interrupts not initialized yet, just spin */
  46         if (irq == -1 || in_nmi())
  47                 return;
  48
  49         /* Guard against reentry. */
  50         local_irq_save(flags);
  51
  52         /* If irq pending already clear it. */
  53         if (xen_test_irq_pending(irq)) {
  54                 xen_clear_irq_pending(irq);
  55         } else if (READ_ONCE(*byte) == val) {
  56                 /* Block until irq becomes pending (or a spurious wakeup) */
  57                 xen_poll_irq(irq);
  58         }
  59
  60         local_irq_restore(flags);
  61 }
  62
  63 static irqreturn_t dummy_handler(int irq, void *dev_id)
  64 {
  65         BUG();
  66         return IRQ_HANDLED;
  67 }
  68
  69 void xen_init_lock_cpu(int cpu)
  70 {
  71         int irq;
  72         char *name;
  73
  74         if (!xen_pvspin) {
  75                 if (cpu == 0)
  76                         static_branch_disable(&virt_spin_lock_key);
  77                 return;
  78         }
  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         if (!xen_pvspin)
 103                 return;
 104
 105         unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
 106         per_cpu(lock_kicker_irq, cpu) = -1;
 107         kfree(per_cpu(irq_name, cpu));
 108         per_cpu(irq_name, cpu) = NULL;
 109 }
 110
 111 PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen);
 112
 113 /*
 114  * Our init of PV spinlocks is split in two init functions due to us
 115  * using paravirt patching and jump labels patching and having to do
 116  * all of this before SMP code is invoked.
 117  *
 118  * The paravirt patching needs to be done _before_ the alternative asm code
 119  * is started, otherwise we would not patch the core kernel code.
 120  */
 121 void __init xen_init_spinlocks(void)
 122 {
 123
 124         /*  Don't need to use pvqspinlock code if there is only 1 vCPU. */
 125         if (num_possible_cpus() == 1)
 126                 xen_pvspin = false;
 127
 128         if (!xen_pvspin) {
 129                 printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
 130                 return;
 131         }
 132         printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
 133
 134         __pv_init_lock_hash();
 135         pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
 136         pv_ops.lock.queued_spin_unlock =
 137                 PV_CALLEE_SAVE(__pv_queued_spin_unlock);
 138         pv_ops.lock.wait = xen_qlock_wait;
 139         pv_ops.lock.kick = xen_qlock_kick;
 140         pv_ops.lock.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen);
 141 }
 142
 143 static __init int xen_parse_nopvspin(char *arg)
 144 {
 145         xen_pvspin = false;
 146         return 0;
 147 }
 148 early_param("xen_nopvspin", xen_parse_nopvspin);
 149