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 13 #include <asm/paravirt.h> 14 #include <asm/qspinlock.h> 15 16 #include <xen/interface/xen.h> 17 #include <xen/events.h> 18 19 #include "xen-ops.h" 20 #include "debugfs.h" 21 22 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1; 23 static DEFINE_PER_CPU(char *, irq_name); 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 46 /* If kicker interrupts not initialized yet, just spin */ 47 if (irq == -1) 48 return; 49 50 /* clear pending */ 51 xen_clear_irq_pending(irq); 52 barrier(); 53 54 /* 55 * We check the byte value after clearing pending IRQ to make sure 56 * that we won't miss a wakeup event because of the clearing. 57 * 58 * The sync_clear_bit() call in xen_clear_irq_pending() is atomic. 59 * So it is effectively a memory barrier for x86. 60 */ 61 if (READ_ONCE(*byte) != val) 62 return; 63 64 /* 65 * If an interrupt happens here, it will leave the wakeup irq 66 * pending, which will cause xen_poll_irq() to return 67 * immediately. 68 */ 69 70 /* Block until irq becomes pending (or perhaps a spurious wakeup) */ 71 xen_poll_irq(irq); 72 } 73 74 static irqreturn_t dummy_handler(int irq, void *dev_id) 75 { 76 BUG(); 77 return IRQ_HANDLED; 78 } 79 80 void xen_init_lock_cpu(int cpu) 81 { 82 int irq; 83 char *name; 84 85 if (!xen_pvspin) { 86 if (cpu == 0) 87 static_branch_disable(&virt_spin_lock_key); 88 return; 89 } 90 91 WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n", 92 cpu, per_cpu(lock_kicker_irq, cpu)); 93 94 name = kasprintf(GFP_KERNEL, "spinlock%d", cpu); 95 irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR, 96 cpu, 97 dummy_handler, 98 IRQF_PERCPU|IRQF_NOBALANCING, 99 name, 100 NULL); 101 102 if (irq >= 0) { 103 disable_irq(irq); /* make sure it's never delivered */ 104 per_cpu(lock_kicker_irq, cpu) = irq; 105 per_cpu(irq_name, cpu) = name; 106 } 107 108 printk("cpu %d spinlock event irq %d\n", cpu, irq); 109 } 110 111 void xen_uninit_lock_cpu(int cpu) 112 { 113 if (!xen_pvspin) 114 return; 115 116 unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL); 117 per_cpu(lock_kicker_irq, cpu) = -1; 118 kfree(per_cpu(irq_name, cpu)); 119 per_cpu(irq_name, cpu) = NULL; 120 } 121 122 PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen); 123 124 /* 125 * Our init of PV spinlocks is split in two init functions due to us 126 * using paravirt patching and jump labels patching and having to do 127 * all of this before SMP code is invoked. 128 * 129 * The paravirt patching needs to be done _before_ the alternative asm code 130 * is started, otherwise we would not patch the core kernel code. 131 */ 132 void __init xen_init_spinlocks(void) 133 { 134 135 if (!xen_pvspin) { 136 printk(KERN_DEBUG "xen: PV spinlocks disabled\n"); 137 return; 138 } 139 printk(KERN_DEBUG "xen: PV spinlocks enabled\n"); 140 141 __pv_init_lock_hash(); 142 pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath; 143 pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock); 144 pv_lock_ops.wait = xen_qlock_wait; 145 pv_lock_ops.kick = xen_qlock_kick; 146 pv_lock_ops.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen); 147 } 148 149 static __init int xen_parse_nopvspin(char *arg) 150 { 151 xen_pvspin = false; 152 return 0; 153 } 154 early_param("xen_nopvspin", xen_parse_nopvspin); 155 156