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 static bool xen_pvspin = true; 22 23 static void xen_qlock_kick(int cpu) 24 { 25 int irq = per_cpu(lock_kicker_irq, cpu); 26 27 /* Don't kick if the target's kicker interrupt is not initialized. */ 28 if (irq == -1) 29 return; 30 31 xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR); 32 } 33 34 /* 35 * Halt the current CPU & release it back to the host 36 */ 37 static void xen_qlock_wait(u8 *byte, u8 val) 38 { 39 int irq = __this_cpu_read(lock_kicker_irq); 40 atomic_t *nest_cnt = this_cpu_ptr(&xen_qlock_wait_nest); 41 42 /* If kicker interrupts not initialized yet, just spin */ 43 if (irq == -1 || in_nmi()) 44 return; 45 46 /* Detect reentry. */ 47 atomic_inc(nest_cnt); 48 49 /* If irq pending already and no nested call clear it. */ 50 if (atomic_read(nest_cnt) == 1 && xen_test_irq_pending(irq)) { 51 xen_clear_irq_pending(irq); 52 } else if (READ_ONCE(*byte) == val) { 53 /* Block until irq becomes pending (or a spurious wakeup) */ 54 xen_poll_irq(irq); 55 } 56 57 atomic_dec(nest_cnt); 58 } 59 60 static irqreturn_t dummy_handler(int irq, void *dev_id) 61 { 62 BUG(); 63 return IRQ_HANDLED; 64 } 65 66 void xen_init_lock_cpu(int cpu) 67 { 68 int irq; 69 char *name; 70 71 if (!xen_pvspin) 72 return; 73 74 WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n", 75 cpu, per_cpu(lock_kicker_irq, cpu)); 76 77 name = kasprintf(GFP_KERNEL, "spinlock%d", cpu); 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 per_cpu(irq_name, cpu) = name; 89 } 90 91 printk("cpu %d spinlock event irq %d\n", cpu, irq); 92 } 93 94 void xen_uninit_lock_cpu(int cpu) 95 { 96 int irq; 97 98 if (!xen_pvspin) 99 return; 100 101 /* 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 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 /* Don't need to use pvqspinlock code if there is only 1 vCPU. */ 128 if (num_possible_cpus() == 1 || nopvspin) 129 xen_pvspin = false; 130 131 if (!xen_pvspin) { 132 printk(KERN_DEBUG "xen: PV spinlocks disabled\n"); 133 static_branch_disable(&virt_spin_lock_key); 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 pr_notice("\"xen_nopvspin\" is deprecated, please use \"nopvspin\" instead\n"); 150 xen_pvspin = false; 151 return 0; 152 } 153 early_param("xen_nopvspin", xen_parse_nopvspin); 154 155