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 /* If irq pending already clear it and return. */ 49 if (xen_test_irq_pending(irq)) { 50 xen_clear_irq_pending(irq); 51 return; 52 } 53 54 if (READ_ONCE(*byte) != val) 55 return; 56 57 /* 58 * If an interrupt happens here, it will leave the wakeup irq 59 * pending, which will cause xen_poll_irq() to return 60 * immediately. 61 */ 62 63 /* Block until irq becomes pending (or perhaps a spurious wakeup) */ 64 xen_poll_irq(irq); 65 } 66 67 static irqreturn_t dummy_handler(int irq, void *dev_id) 68 { 69 BUG(); 70 return IRQ_HANDLED; 71 } 72 73 void xen_init_lock_cpu(int cpu) 74 { 75 int irq; 76 char *name; 77 78 if (!xen_pvspin) { 79 if (cpu == 0) 80 static_branch_disable(&virt_spin_lock_key); 81 return; 82 } 83 84 WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n", 85 cpu, per_cpu(lock_kicker_irq, cpu)); 86 87 name = kasprintf(GFP_KERNEL, "spinlock%d", cpu); 88 irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR, 89 cpu, 90 dummy_handler, 91 IRQF_PERCPU|IRQF_NOBALANCING, 92 name, 93 NULL); 94 95 if (irq >= 0) { 96 disable_irq(irq); /* make sure it's never delivered */ 97 per_cpu(lock_kicker_irq, cpu) = irq; 98 per_cpu(irq_name, cpu) = name; 99 } 100 101 printk("cpu %d spinlock event irq %d\n", cpu, irq); 102 } 103 104 void xen_uninit_lock_cpu(int cpu) 105 { 106 if (!xen_pvspin) 107 return; 108 109 unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL); 110 per_cpu(lock_kicker_irq, cpu) = -1; 111 kfree(per_cpu(irq_name, cpu)); 112 per_cpu(irq_name, cpu) = NULL; 113 } 114 115 PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen); 116 117 /* 118 * Our init of PV spinlocks is split in two init functions due to us 119 * using paravirt patching and jump labels patching and having to do 120 * all of this before SMP code is invoked. 121 * 122 * The paravirt patching needs to be done _before_ the alternative asm code 123 * is started, otherwise we would not patch the core kernel code. 124 */ 125 void __init xen_init_spinlocks(void) 126 { 127 128 /* Don't need to use pvqspinlock code if there is only 1 vCPU. */ 129 if (num_possible_cpus() == 1) 130 xen_pvspin = false; 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_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath; 140 pv_ops.lock.queued_spin_unlock = 141 PV_CALLEE_SAVE(__pv_queued_spin_unlock); 142 pv_ops.lock.wait = xen_qlock_wait; 143 pv_ops.lock.kick = xen_qlock_kick; 144 pv_ops.lock.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen); 145 } 146 147 static __init int xen_parse_nopvspin(char *arg) 148 { 149 xen_pvspin = false; 150 return 0; 151 } 152 early_param("xen_nopvspin", xen_parse_nopvspin); 153 154