arch/x86/xen/spinlock.c

   1 /*
   2  * Split spinlock implementation out into its own file, so it can be
   3  * compiled in a FTRACE-compatible way.
   4  */
   5 #include <linux/kernel_stat.h>
   6 #include <linux/spinlock.h>
   7 #include <linux/debugfs.h>
   8 #include <linux/log2.h>
   9 #include <linux/gfp.h>
  10 #include <linux/slab.h>
  11 #include <linux/atomic.h>
  12
  13 #include <asm/paravirt.h>
  14
  15 #include <xen/interface/xen.h>
  16 #include <xen/events.h>
  17
  18 #include "xen-ops.h"
  19 #include "debugfs.h"
  20
  21 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
  22 static DEFINE_PER_CPU(char *, irq_name);
  23 static DEFINE_PER_CPU(atomic_t, xen_qlock_wait_nest);
  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         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                 return;
  78
  79         WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
  80              cpu, per_cpu(lock_kicker_irq, cpu));
  81
  82         name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
  83         irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
  84                                      cpu,
  85                                      dummy_handler,
  86                                      IRQF_PERCPU|IRQF_NOBALANCING,
  87                                      name,
  88                                      NULL);
  89
  90         if (irq >= 0) {
  91                 disable_irq(irq); /* make sure it's never delivered */
  92                 per_cpu(lock_kicker_irq, cpu) = irq;
  93                 per_cpu(irq_name, cpu) = name;
  94         }
  95
  96         printk("cpu %d spinlock event irq %d\n", cpu, irq);
  97 }
  98
  99 void xen_uninit_lock_cpu(int cpu)
 100 {
 101         int irq;
 102
 103         if (!xen_pvspin)
 104                 return;
 105
 106         /*
 107          * When booting the kernel with 'mitigations=auto,nosmt', the secondary
 108          * CPUs are not activated, and lock_kicker_irq is not initialized.
 109          */
 110         irq = per_cpu(lock_kicker_irq, cpu);
 111         if (irq == -1)
 112                 return;
 113
 114         unbind_from_irqhandler(irq, 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
 121 /*
 122  * Our init of PV spinlocks is split in two init functions due to us
 123  * using paravirt patching and jump labels patching and having to do
 124  * all of this before SMP code is invoked.
 125  *
 126  * The paravirt patching needs to be done _before_ the alternative asm code
 127  * is started, otherwise we would not patch the core kernel code.
 128  */
 129 void __init xen_init_spinlocks(void)
 130 {
 131
 132         if (!xen_pvspin) {
 133                 printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
 134                 return;
 135         }
 136         printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
 137
 138         __pv_init_lock_hash();
 139         pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
 140         pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
 141         pv_lock_ops.wait = xen_qlock_wait;
 142         pv_lock_ops.kick = xen_qlock_kick;
 143 }
 144
 145 /*
 146  * While the jump_label init code needs to happend _after_ the jump labels are
 147  * enabled and before SMP is started. Hence we use pre-SMP initcall level
 148  * init. We cannot do it in xen_init_spinlocks as that is done before
 149  * jump labels are activated.
 150  */
 151 static __init int xen_init_spinlocks_jump(void)
 152 {
 153         if (!xen_pvspin)
 154                 return 0;
 155
 156         if (!xen_domain())
 157                 return 0;
 158
 159         static_key_slow_inc(&paravirt_ticketlocks_enabled);
 160         return 0;
 161 }
 162 early_initcall(xen_init_spinlocks_jump);
 163
 164 static __init int xen_parse_nopvspin(char *arg)
 165 {
 166         xen_pvspin = false;
 167         return 0;
 168 }
 169 early_param("xen_nopvspin", xen_parse_nopvspin);
 170