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 12 #include <asm/paravirt.h> 13 14 #include <xen/interface/xen.h> 15 #include <xen/events.h> 16 17 #include "xen-ops.h" 18 #include "debugfs.h" 19 20 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1; 21 static DEFINE_PER_CPU(char *, irq_name); 22 static bool xen_pvspin = true; 23 24 #include <asm/qspinlock.h> 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 int irq = __this_cpu_read(lock_kicker_irq); 43 44 /* If kicker interrupts not initialized yet, just spin */ 45 if (irq == -1) 46 return; 47 48 /* clear pending */ 49 xen_clear_irq_pending(irq); 50 barrier(); 51 52 /* 53 * We check the byte value after clearing pending IRQ to make sure 54 * that we won't miss a wakeup event because of the clearing. 55 * 56 * The sync_clear_bit() call in xen_clear_irq_pending() is atomic. 57 * So it is effectively a memory barrier for x86. 58 */ 59 if (READ_ONCE(*byte) != val) 60 return; 61 62 /* 63 * If an interrupt happens here, it will leave the wakeup irq 64 * pending, which will cause xen_poll_irq() to return 65 * immediately. 66 */ 67 68 /* Block until irq becomes pending (or perhaps a spurious wakeup) */ 69 xen_poll_irq(irq); 70 } 71 72 static irqreturn_t dummy_handler(int irq, void *dev_id) 73 { 74 BUG(); 75 return IRQ_HANDLED; 76 } 77 78 void xen_init_lock_cpu(int cpu) 79 { 80 int irq; 81 char *name; 82 83 if (!xen_pvspin) 84 return; 85 86 WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n", 87 cpu, per_cpu(lock_kicker_irq, cpu)); 88 89 name = kasprintf(GFP_KERNEL, "spinlock%d", cpu); 90 irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR, 91 cpu, 92 dummy_handler, 93 IRQF_PERCPU|IRQF_NOBALANCING, 94 name, 95 NULL); 96 97 if (irq >= 0) { 98 disable_irq(irq); /* make sure it's never delivered */ 99 per_cpu(lock_kicker_irq, cpu) = irq; 100 per_cpu(irq_name, cpu) = name; 101 } 102 103 printk("cpu %d spinlock event irq %d\n", cpu, irq); 104 } 105 106 void xen_uninit_lock_cpu(int cpu) 107 { 108 if (!xen_pvspin) 109 return; 110 111 unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL); 112 per_cpu(lock_kicker_irq, cpu) = -1; 113 kfree(per_cpu(irq_name, cpu)); 114 per_cpu(irq_name, cpu) = NULL; 115 } 116 117 PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen); 118 119 /* 120 * Our init of PV spinlocks is split in two init functions due to us 121 * using paravirt patching and jump labels patching and having to do 122 * all of this before SMP code is invoked. 123 * 124 * The paravirt patching needs to be done _before_ the alternative asm code 125 * is started, otherwise we would not patch the core kernel code. 126 */ 127 void __init xen_init_spinlocks(void) 128 { 129 130 if (!xen_pvspin) { 131 printk(KERN_DEBUG "xen: PV spinlocks disabled\n"); 132 return; 133 } 134 printk(KERN_DEBUG "xen: PV spinlocks enabled\n"); 135 136 __pv_init_lock_hash(); 137 pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath; 138 pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock); 139 pv_lock_ops.wait = xen_qlock_wait; 140 pv_lock_ops.kick = xen_qlock_kick; 141 pv_lock_ops.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen); 142 } 143 144 static __init int xen_parse_nopvspin(char *arg) 145 { 146 xen_pvspin = false; 147 return 0; 148 } 149 early_param("xen_nopvspin", xen_parse_nopvspin); 150 151