xref: /openbmc/linux/arch/x86/xen/spinlock.c (revision 6aa7de05)
1 /*
2  * Split spinlock implementation out into its own file, so it can be
3  * compiled in a FTRACE-compatible way.
4  */
5 #include <linux/kernel_stat.h>
6 #include <linux/spinlock.h>
7 #include <linux/debugfs.h>
8 #include <linux/log2.h>
9 #include <linux/gfp.h>
10 #include <linux/slab.h>
11 
12 #include <asm/paravirt.h>
13 #include <asm/qspinlock.h>
14 
15 #include <xen/interface/xen.h>
16 #include <xen/events.h>
17 
18 #include "xen-ops.h"
19 #include "debugfs.h"
20 
21 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
22 static DEFINE_PER_CPU(char *, irq_name);
23 static bool xen_pvspin = true;
24 
25 #include <asm/qspinlock.h>
26 
27 static void xen_qlock_kick(int cpu)
28 {
29 	int irq = per_cpu(lock_kicker_irq, cpu);
30 
31 	/* Don't kick if the target's kicker interrupt is not initialized. */
32 	if (irq == -1)
33 		return;
34 
35 	xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
36 }
37 
38 /*
39  * Halt the current CPU & release it back to the host
40  */
41 static void xen_qlock_wait(u8 *byte, u8 val)
42 {
43 	int irq = __this_cpu_read(lock_kicker_irq);
44 
45 	/* If kicker interrupts not initialized yet, just spin */
46 	if (irq == -1)
47 		return;
48 
49 	/* clear pending */
50 	xen_clear_irq_pending(irq);
51 	barrier();
52 
53 	/*
54 	 * We check the byte value after clearing pending IRQ to make sure
55 	 * that we won't miss a wakeup event because of the clearing.
56 	 *
57 	 * The sync_clear_bit() call in xen_clear_irq_pending() is atomic.
58 	 * So it is effectively a memory barrier for x86.
59 	 */
60 	if (READ_ONCE(*byte) != val)
61 		return;
62 
63 	/*
64 	 * If an interrupt happens here, it will leave the wakeup irq
65 	 * pending, which will cause xen_poll_irq() to return
66 	 * immediately.
67 	 */
68 
69 	/* Block until irq becomes pending (or perhaps a spurious wakeup) */
70 	xen_poll_irq(irq);
71 }
72 
73 static irqreturn_t dummy_handler(int irq, void *dev_id)
74 {
75 	BUG();
76 	return IRQ_HANDLED;
77 }
78 
79 void xen_init_lock_cpu(int cpu)
80 {
81 	int irq;
82 	char *name;
83 
84 	if (!xen_pvspin)
85 		return;
86 
87 	WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
88 	     cpu, per_cpu(lock_kicker_irq, cpu));
89 
90 	name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
91 	irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
92 				     cpu,
93 				     dummy_handler,
94 				     IRQF_PERCPU|IRQF_NOBALANCING,
95 				     name,
96 				     NULL);
97 
98 	if (irq >= 0) {
99 		disable_irq(irq); /* make sure it's never delivered */
100 		per_cpu(lock_kicker_irq, cpu) = irq;
101 		per_cpu(irq_name, cpu) = name;
102 	}
103 
104 	printk("cpu %d spinlock event irq %d\n", cpu, irq);
105 }
106 
107 void xen_uninit_lock_cpu(int cpu)
108 {
109 	if (!xen_pvspin)
110 		return;
111 
112 	unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
113 	per_cpu(lock_kicker_irq, cpu) = -1;
114 	kfree(per_cpu(irq_name, cpu));
115 	per_cpu(irq_name, cpu) = NULL;
116 }
117 
118 PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen);
119 
120 /*
121  * Our init of PV spinlocks is split in two init functions due to us
122  * using paravirt patching and jump labels patching and having to do
123  * all of this before SMP code is invoked.
124  *
125  * The paravirt patching needs to be done _before_ the alternative asm code
126  * is started, otherwise we would not patch the core kernel code.
127  */
128 void __init xen_init_spinlocks(void)
129 {
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_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
140 	pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
141 	pv_lock_ops.wait = xen_qlock_wait;
142 	pv_lock_ops.kick = xen_qlock_kick;
143 	pv_lock_ops.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen);
144 }
145 
146 static __init int xen_parse_nopvspin(char *arg)
147 {
148 	xen_pvspin = false;
149 	return 0;
150 }
151 early_param("xen_nopvspin", xen_parse_nopvspin);
152 
153