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 #include <linux/atomic.h> 13 14 #include <asm/paravirt.h> 15 #include <asm/qspinlock.h> 16 17 #include <xen/interface/xen.h> 18 #include <xen/events.h> 19 20 #include "xen-ops.h" 21 #include "debugfs.h" 22 23 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1; 24 static DEFINE_PER_CPU(char *, irq_name); 25 static DEFINE_PER_CPU(atomic_t, xen_qlock_wait_nest); 26 static bool xen_pvspin = true; 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 atomic_t *nest_cnt = this_cpu_ptr(&xen_qlock_wait_nest); 46 47 /* If kicker interrupts not initialized yet, just spin */ 48 if (irq == -1 || in_nmi()) 49 return; 50 51 /* Detect reentry. */ 52 atomic_inc(nest_cnt); 53 54 /* If irq pending already and no nested call clear it. */ 55 if (atomic_read(nest_cnt) == 1 && xen_test_irq_pending(irq)) { 56 xen_clear_irq_pending(irq); 57 } else if (READ_ONCE(*byte) == val) { 58 /* Block until irq becomes pending (or a spurious wakeup) */ 59 xen_poll_irq(irq); 60 } 61 62 atomic_dec(nest_cnt); 63 } 64 65 static irqreturn_t dummy_handler(int irq, void *dev_id) 66 { 67 BUG(); 68 return IRQ_HANDLED; 69 } 70 71 void xen_init_lock_cpu(int cpu) 72 { 73 int irq; 74 char *name; 75 76 if (!xen_pvspin) { 77 if (cpu == 0) 78 static_branch_disable(&virt_spin_lock_key); 79 return; 80 } 81 82 WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n", 83 cpu, per_cpu(lock_kicker_irq, cpu)); 84 85 name = kasprintf(GFP_KERNEL, "spinlock%d", cpu); 86 irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR, 87 cpu, 88 dummy_handler, 89 IRQF_PERCPU|IRQF_NOBALANCING, 90 name, 91 NULL); 92 93 if (irq >= 0) { 94 disable_irq(irq); /* make sure it's never delivered */ 95 per_cpu(lock_kicker_irq, cpu) = irq; 96 per_cpu(irq_name, cpu) = name; 97 } 98 99 printk("cpu %d spinlock event irq %d\n", cpu, irq); 100 } 101 102 void xen_uninit_lock_cpu(int cpu) 103 { 104 if (!xen_pvspin) 105 return; 106 107 unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL); 108 per_cpu(lock_kicker_irq, cpu) = -1; 109 kfree(per_cpu(irq_name, cpu)); 110 per_cpu(irq_name, cpu) = NULL; 111 } 112 113 PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen); 114 115 /* 116 * Our init of PV spinlocks is split in two init functions due to us 117 * using paravirt patching and jump labels patching and having to do 118 * all of this before SMP code is invoked. 119 * 120 * The paravirt patching needs to be done _before_ the alternative asm code 121 * is started, otherwise we would not patch the core kernel code. 122 */ 123 void __init xen_init_spinlocks(void) 124 { 125 126 /* Don't need to use pvqspinlock code if there is only 1 vCPU. */ 127 if (num_possible_cpus() == 1) 128 xen_pvspin = false; 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_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath; 138 pv_ops.lock.queued_spin_unlock = 139 PV_CALLEE_SAVE(__pv_queued_spin_unlock); 140 pv_ops.lock.wait = xen_qlock_wait; 141 pv_ops.lock.kick = xen_qlock_kick; 142 pv_ops.lock.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen); 143 } 144 145 static __init int xen_parse_nopvspin(char *arg) 146 { 147 xen_pvspin = false; 148 return 0; 149 } 150 early_param("xen_nopvspin", xen_parse_nopvspin); 151 152