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