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 #include <linux/atomic.h>
  13
  14 #include <asm/paravirt.h>
  15 #include <asm/qspinlock.h>
  16
  17 #include <xen/interface/xen.h>
  18 #include <xen/events.h>
  19
  20 #include "xen-ops.h"
  21 #include "debugfs.h"
  22
  23 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
  24 static DEFINE_PER_CPU(char *, irq_name);
  25 static DEFINE_PER_CPU(atomic_t, xen_qlock_wait_nest);
  26 static bool xen_pvspin = true;
  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         atomic_t *nest_cnt = this_cpu_ptr(&xen_qlock_wait_nest);
  46
  47         /* If kicker interrupts not initialized yet, just spin */
  48         if (irq == -1 || in_nmi())
  49                 return;
  50
  51         /* Detect reentry. */
  52         atomic_inc(nest_cnt);
  53
  54         /* If irq pending already and no nested call clear it. */
  55         if (atomic_read(nest_cnt) == 1 && xen_test_irq_pending(irq)) {
  56                 xen_clear_irq_pending(irq);
  57         } else if (READ_ONCE(*byte) == val) {
  58                 /* Block until irq becomes pending (or a spurious wakeup) */
  59                 xen_poll_irq(irq);
  60         }
  61
  62         atomic_dec(nest_cnt);
  63 }
  64
  65 static irqreturn_t dummy_handler(int irq, void *dev_id)
  66 {
  67         BUG();
  68         return IRQ_HANDLED;
  69 }
  70
  71 void xen_init_lock_cpu(int cpu)
  72 {
  73         int irq;
  74         char *name;
  75
  76         if (!xen_pvspin) {
  77                 if (cpu == 0)
  78                         static_branch_disable(&virt_spin_lock_key);
  79                 return;
  80         }
  81
  82         WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
  83              cpu, per_cpu(lock_kicker_irq, cpu));
  84
  85         name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
  86         irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
  87                                      cpu,
  88                                      dummy_handler,
  89                                      IRQF_PERCPU|IRQF_NOBALANCING,
  90                                      name,
  91                                      NULL);
  92
  93         if (irq >= 0) {
  94                 disable_irq(irq); /* make sure it's never delivered */
  95                 per_cpu(lock_kicker_irq, cpu) = irq;
  96                 per_cpu(irq_name, cpu) = name;
  97         }
  98
  99         printk("cpu %d spinlock event irq %d\n", cpu, irq);
 100 }
 101
 102 void xen_uninit_lock_cpu(int cpu)
 103 {
 104         int irq;
 105
 106         if (!xen_pvspin)
 107                 return;
 108
 109         /*
 110          * When booting the kernel with 'mitigations=auto,nosmt', the secondary
 111          * CPUs are not activated, and lock_kicker_irq is not initialized.
 112          */
 113         irq = per_cpu(lock_kicker_irq, cpu);
 114         if (irq == -1)
 115                 return;
 116
 117         unbind_from_irqhandler(irq, NULL);
 118         per_cpu(lock_kicker_irq, cpu) = -1;
 119         kfree(per_cpu(irq_name, cpu));
 120         per_cpu(irq_name, cpu) = NULL;
 121 }
 122
 123 PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen);
 124
 125 /*
 126  * Our init of PV spinlocks is split in two init functions due to us
 127  * using paravirt patching and jump labels patching and having to do
 128  * all of this before SMP code is invoked.
 129  *
 130  * The paravirt patching needs to be done _before_ the alternative asm code
 131  * is started, otherwise we would not patch the core kernel code.
 132  */
 133 void __init xen_init_spinlocks(void)
 134 {
 135
 136         /*  Don't need to use pvqspinlock code if there is only 1 vCPU. */
 137         if (num_possible_cpus() == 1)
 138                 xen_pvspin = false;
 139
 140         if (!xen_pvspin) {
 141                 printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
 142                 return;
 143         }
 144         printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
 145
 146         __pv_init_lock_hash();
 147         pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
 148         pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
 149         pv_lock_ops.wait = xen_qlock_wait;
 150         pv_lock_ops.kick = xen_qlock_kick;
 151         pv_lock_ops.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen);
 152 }
 153
 154 static __init int xen_parse_nopvspin(char *arg)
 155 {
 156         xen_pvspin = false;
 157         return 0;
 158 }
 159 early_param("xen_nopvspin", xen_parse_nopvspin);
 160