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 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 if (cpu == 0) 85 static_branch_disable(&virt_spin_lock_key); 86 return; 87 } 88 89 WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n", 90 cpu, per_cpu(lock_kicker_irq, cpu)); 91 92 name = kasprintf(GFP_KERNEL, "spinlock%d", cpu); 93 irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR, 94 cpu, 95 dummy_handler, 96 IRQF_PERCPU|IRQF_NOBALANCING, 97 name, 98 NULL); 99 100 if (irq >= 0) { 101 disable_irq(irq); /* make sure it's never delivered */ 102 per_cpu(lock_kicker_irq, cpu) = irq; 103 per_cpu(irq_name, cpu) = name; 104 } 105 106 printk("cpu %d spinlock event irq %d\n", cpu, irq); 107 } 108 109 void xen_uninit_lock_cpu(int cpu) 110 { 111 if (!xen_pvspin) 112 return; 113 114 unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), 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 PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen); 121 122 /* 123 * Our init of PV spinlocks is split in two init functions due to us 124 * using paravirt patching and jump labels patching and having to do 125 * all of this before SMP code is invoked. 126 * 127 * The paravirt patching needs to be done _before_ the alternative asm code 128 * is started, otherwise we would not patch the core kernel code. 129 */ 130 void __init xen_init_spinlocks(void) 131 { 132 133 /* Don't need to use pvqspinlock code if there is only 1 vCPU. */ 134 if (num_possible_cpus() == 1) 135 xen_pvspin = false; 136 137 if (!xen_pvspin) { 138 printk(KERN_DEBUG "xen: PV spinlocks disabled\n"); 139 return; 140 } 141 printk(KERN_DEBUG "xen: PV spinlocks enabled\n"); 142 143 __pv_init_lock_hash(); 144 pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath; 145 pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock); 146 pv_lock_ops.wait = xen_qlock_wait; 147 pv_lock_ops.kick = xen_qlock_kick; 148 pv_lock_ops.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen); 149 } 150 151 static __init int xen_parse_nopvspin(char *arg) 152 { 153 xen_pvspin = false; 154 return 0; 155 } 156 early_param("xen_nopvspin", xen_parse_nopvspin); 157 158