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/paravirt.h> 12 #include <asm/qspinlock.h> 13 14 #include <xen/events.h> 15 16 #include "xen-ops.h" 17 18 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1; 19 static DEFINE_PER_CPU(char *, irq_name); 20 static DEFINE_PER_CPU(atomic_t, xen_qlock_wait_nest); 21 22 static void xen_qlock_kick(int cpu) 23 { 24 int irq = per_cpu(lock_kicker_irq, cpu); 25 26 /* Don't kick if the target's kicker interrupt is not initialized. */ 27 if (irq == -1) 28 return; 29 30 xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR); 31 } 32 33 /* 34 * Halt the current CPU & release it back to the host 35 */ 36 static void xen_qlock_wait(u8 *byte, u8 val) 37 { 38 int irq = __this_cpu_read(lock_kicker_irq); 39 atomic_t *nest_cnt = this_cpu_ptr(&xen_qlock_wait_nest); 40 41 /* If kicker interrupts not initialized yet, just spin */ 42 if (irq == -1 || in_nmi()) 43 return; 44 45 /* Detect reentry. */ 46 atomic_inc(nest_cnt); 47 48 /* If irq pending already and no nested call clear it. */ 49 if (atomic_read(nest_cnt) == 1 && xen_test_irq_pending(irq)) { 50 xen_clear_irq_pending(irq); 51 } else if (READ_ONCE(*byte) == val) { 52 /* Block until irq becomes pending (or a spurious wakeup) */ 53 xen_poll_irq(irq); 54 } 55 56 atomic_dec(nest_cnt); 57 } 58 59 static irqreturn_t dummy_handler(int irq, void *dev_id) 60 { 61 BUG(); 62 return IRQ_HANDLED; 63 } 64 65 void xen_init_lock_cpu(int cpu) 66 { 67 int irq; 68 char *name; 69 70 if (nopvspin) 71 return; 72 73 WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n", 74 cpu, per_cpu(lock_kicker_irq, cpu)); 75 76 name = kasprintf(GFP_KERNEL, "spinlock%d", cpu); 77 per_cpu(irq_name, cpu) = name; 78 irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR, 79 cpu, 80 dummy_handler, 81 IRQF_PERCPU|IRQF_NOBALANCING, 82 name, 83 NULL); 84 85 if (irq >= 0) { 86 disable_irq(irq); /* make sure it's never delivered */ 87 per_cpu(lock_kicker_irq, cpu) = irq; 88 } 89 90 printk("cpu %d spinlock event irq %d\n", cpu, irq); 91 } 92 93 void xen_uninit_lock_cpu(int cpu) 94 { 95 int irq; 96 97 if (nopvspin) 98 return; 99 100 kfree(per_cpu(irq_name, cpu)); 101 per_cpu(irq_name, cpu) = NULL; 102 /* 103 * When booting the kernel with 'mitigations=auto,nosmt', the secondary 104 * CPUs are not activated, and lock_kicker_irq is not initialized. 105 */ 106 irq = per_cpu(lock_kicker_irq, cpu); 107 if (irq == -1) 108 return; 109 110 unbind_from_irqhandler(irq, NULL); 111 per_cpu(lock_kicker_irq, cpu) = -1; 112 } 113 114 PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen); 115 116 /* 117 * Our init of PV spinlocks is split in two init functions due to us 118 * using paravirt patching and jump labels patching and having to do 119 * all of this before SMP code is invoked. 120 * 121 * The paravirt patching needs to be done _before_ the alternative asm code 122 * is started, otherwise we would not patch the core kernel code. 123 */ 124 void __init xen_init_spinlocks(void) 125 { 126 /* Don't need to use pvqspinlock code if there is only 1 vCPU. */ 127 if (num_possible_cpus() == 1) 128 nopvspin = true; 129 130 if (nopvspin) { 131 printk(KERN_DEBUG "xen: PV spinlocks disabled\n"); 132 static_branch_disable(&virt_spin_lock_key); 133 return; 134 } 135 printk(KERN_DEBUG "xen: PV spinlocks enabled\n"); 136 137 __pv_init_lock_hash(); 138 pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath; 139 pv_ops.lock.queued_spin_unlock = 140 PV_CALLEE_SAVE(__pv_queued_spin_unlock); 141 pv_ops.lock.wait = xen_qlock_wait; 142 pv_ops.lock.kick = xen_qlock_kick; 143 pv_ops.lock.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen); 144 } 145