xref: /openbmc/linux/arch/x86/xen/spinlock.c (revision ca84ce15)
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 
xen_qlock_kick(int cpu)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  */
xen_qlock_wait(u8 * byte,u8 val)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 
dummy_handler(int irq,void * dev_id)60 static irqreturn_t dummy_handler(int irq, void *dev_id)
61 {
62 	BUG();
63 	return IRQ_HANDLED;
64 }
65 
xen_init_lock_cpu(int cpu)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 	per_cpu(irq_name, cpu) = name;
79 	irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
80 				     cpu,
81 				     dummy_handler,
82 				     IRQF_PERCPU|IRQF_NOBALANCING,
83 				     name,
84 				     NULL);
85 
86 	if (irq >= 0) {
87 		disable_irq(irq); /* make sure it's never delivered */
88 		per_cpu(lock_kicker_irq, cpu) = irq;
89 	}
90 
91 	printk("cpu %d spinlock event irq %d\n", cpu, irq);
92 }
93 
xen_uninit_lock_cpu(int cpu)94 void xen_uninit_lock_cpu(int cpu)
95 {
96 	int irq;
97 
98 	if (!xen_pvspin)
99 		return;
100 
101 	kfree(per_cpu(irq_name, cpu));
102 	per_cpu(irq_name, cpu) = NULL;
103 	/*
104 	 * When booting the kernel with 'mitigations=auto,nosmt', the secondary
105 	 * CPUs are not activated, and lock_kicker_irq is not initialized.
106 	 */
107 	irq = per_cpu(lock_kicker_irq, cpu);
108 	if (irq == -1)
109 		return;
110 
111 	unbind_from_irqhandler(irq, NULL);
112 	per_cpu(lock_kicker_irq, cpu) = -1;
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  */
xen_init_spinlocks(void)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 
xen_parse_nopvspin(char * arg)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