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 #include <asm/qspinlock.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 bool xen_pvspin = true; 24 25 #include <asm/qspinlock.h> 26 27 static void xen_qlock_kick(int cpu) 28 { 29 int irq = per_cpu(lock_kicker_irq, cpu); 30 31 /* Don't kick if the target's kicker interrupt is not initialized. */ 32 if (irq == -1) 33 return; 34 35 xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR); 36 } 37 38 /* 39 * Halt the current CPU & release it back to the host 40 */ 41 static void xen_qlock_wait(u8 *byte, u8 val) 42 { 43 int irq = __this_cpu_read(lock_kicker_irq); 44 45 /* If kicker interrupts not initialized yet, just spin */ 46 if (irq == -1) 47 return; 48 49 /* clear pending */ 50 xen_clear_irq_pending(irq); 51 barrier(); 52 53 /* 54 * We check the byte value after clearing pending IRQ to make sure 55 * that we won't miss a wakeup event because of the clearing. 56 * 57 * The sync_clear_bit() call in xen_clear_irq_pending() is atomic. 58 * So it is effectively a memory barrier for x86. 59 */ 60 if (READ_ONCE(*byte) != val) 61 return; 62 63 /* 64 * If an interrupt happens here, it will leave the wakeup irq 65 * pending, which will cause xen_poll_irq() to return 66 * immediately. 67 */ 68 69 /* Block until irq becomes pending (or perhaps a spurious wakeup) */ 70 xen_poll_irq(irq); 71 } 72 73 static irqreturn_t dummy_handler(int irq, void *dev_id) 74 { 75 BUG(); 76 return IRQ_HANDLED; 77 } 78 79 void xen_init_lock_cpu(int cpu) 80 { 81 int irq; 82 char *name; 83 84 if (!xen_pvspin) 85 return; 86 87 WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n", 88 cpu, per_cpu(lock_kicker_irq, cpu)); 89 90 name = kasprintf(GFP_KERNEL, "spinlock%d", cpu); 91 irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR, 92 cpu, 93 dummy_handler, 94 IRQF_PERCPU|IRQF_NOBALANCING, 95 name, 96 NULL); 97 98 if (irq >= 0) { 99 disable_irq(irq); /* make sure it's never delivered */ 100 per_cpu(lock_kicker_irq, cpu) = irq; 101 per_cpu(irq_name, cpu) = name; 102 } 103 104 printk("cpu %d spinlock event irq %d\n", cpu, irq); 105 } 106 107 void xen_uninit_lock_cpu(int cpu) 108 { 109 if (!xen_pvspin) 110 return; 111 112 unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL); 113 per_cpu(lock_kicker_irq, cpu) = -1; 114 kfree(per_cpu(irq_name, cpu)); 115 per_cpu(irq_name, cpu) = NULL; 116 } 117 118 PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen); 119 120 /* 121 * Our init of PV spinlocks is split in two init functions due to us 122 * using paravirt patching and jump labels patching and having to do 123 * all of this before SMP code is invoked. 124 * 125 * The paravirt patching needs to be done _before_ the alternative asm code 126 * is started, otherwise we would not patch the core kernel code. 127 */ 128 void __init xen_init_spinlocks(void) 129 { 130 131 if (!xen_pvspin) { 132 printk(KERN_DEBUG "xen: PV spinlocks disabled\n"); 133 static_branch_disable(&virt_spin_lock_key); 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 pv_lock_ops.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen); 144 } 145 146 static __init int xen_parse_nopvspin(char *arg) 147 { 148 xen_pvspin = false; 149 return 0; 150 } 151 early_param("xen_nopvspin", xen_parse_nopvspin); 152 153