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.h> 7 #include <linux/spinlock.h> 8 #include <linux/slab.h> 9 #include <linux/atomic.h> 10 11 #include <asm/qspinlock.h> 12 13 #include <xen/events.h> 14 15 #include "xen-ops.h" 16 17 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1; 18 static DEFINE_PER_CPU(char *, irq_name); 19 static DEFINE_PER_CPU(atomic_t, xen_qlock_wait_nest); 20 21 static void xen_qlock_kick(int cpu) 22 { 23 int irq = per_cpu(lock_kicker_irq, cpu); 24 25 /* Don't kick if the target's kicker interrupt is not initialized. */ 26 if (irq == -1) 27 return; 28 29 xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR); 30 } 31 32 /* 33 * Halt the current CPU & release it back to the host 34 */ 35 static void xen_qlock_wait(u8 *byte, u8 val) 36 { 37 int irq = __this_cpu_read(lock_kicker_irq); 38 atomic_t *nest_cnt = this_cpu_ptr(&xen_qlock_wait_nest); 39 40 /* If kicker interrupts not initialized yet, just spin */ 41 if (irq == -1 || in_nmi()) 42 return; 43 44 /* Detect reentry. */ 45 atomic_inc(nest_cnt); 46 47 /* If irq pending already and no nested call clear it. */ 48 if (atomic_read(nest_cnt) == 1 && xen_test_irq_pending(irq)) { 49 xen_clear_irq_pending(irq); 50 } else if (READ_ONCE(*byte) == val) { 51 /* Block until irq becomes pending (or a spurious wakeup) */ 52 xen_poll_irq(irq); 53 } 54 55 atomic_dec(nest_cnt); 56 } 57 58 static irqreturn_t dummy_handler(int irq, void *dev_id) 59 { 60 BUG(); 61 return IRQ_HANDLED; 62 } 63 64 void xen_init_lock_cpu(int cpu) 65 { 66 int irq; 67 char *name; 68 69 if (nopvspin) 70 return; 71 72 WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n", 73 cpu, per_cpu(lock_kicker_irq, cpu)); 74 75 name = kasprintf(GFP_KERNEL, "spinlock%d", cpu); 76 per_cpu(irq_name, cpu) = name; 77 irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR, 78 cpu, 79 dummy_handler, 80 IRQF_PERCPU|IRQF_NOBALANCING, 81 name, 82 NULL); 83 84 if (irq >= 0) { 85 disable_irq(irq); /* make sure it's never delivered */ 86 per_cpu(lock_kicker_irq, cpu) = irq; 87 } 88 89 printk("cpu %d spinlock event irq %d\n", cpu, irq); 90 } 91 92 void xen_uninit_lock_cpu(int cpu) 93 { 94 int irq; 95 96 if (nopvspin) 97 return; 98 99 kfree(per_cpu(irq_name, cpu)); 100 per_cpu(irq_name, cpu) = NULL; 101 /* 102 * When booting the kernel with 'mitigations=auto,nosmt', the secondary 103 * CPUs are not activated, and lock_kicker_irq is not initialized. 104 */ 105 irq = per_cpu(lock_kicker_irq, cpu); 106 if (irq == -1) 107 return; 108 109 unbind_from_irqhandler(irq, NULL); 110 per_cpu(lock_kicker_irq, cpu) = -1; 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 /* Don't need to use pvqspinlock code if there is only 1 vCPU. */ 126 if (num_possible_cpus() == 1) 127 nopvspin = true; 128 129 if (nopvspin) { 130 printk(KERN_DEBUG "xen: PV spinlocks disabled\n"); 131 static_branch_disable(&virt_spin_lock_key); 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