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_stat.h>
7 #include <linux/spinlock.h>
8 #include <linux/debugfs.h>
9 #include <linux/log2.h>
10 #include <linux/gfp.h>
11 #include <linux/slab.h>
12 #include <linux/atomic.h>
13
14 #include <asm/paravirt.h>
15 #include <asm/qspinlock.h>
16
17 #include <xen/interface/xen.h>
18 #include <xen/events.h>
19
20 #include "xen-ops.h"
21 #include "debugfs.h"
22
23 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
24 static DEFINE_PER_CPU(char *, irq_name);
25 static DEFINE_PER_CPU(atomic_t, xen_qlock_wait_nest);
26 static bool xen_pvspin = true;
27
xen_qlock_kick(int cpu)28 static void xen_qlock_kick(int cpu)
29 {
30 int irq = per_cpu(lock_kicker_irq, cpu);
31
32 /* Don't kick if the target's kicker interrupt is not initialized. */
33 if (irq == -1)
34 return;
35
36 xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
37 }
38
39 /*
40 * Halt the current CPU & release it back to the host
41 */
xen_qlock_wait(u8 * byte,u8 val)42 static void xen_qlock_wait(u8 *byte, u8 val)
43 {
44 int irq = __this_cpu_read(lock_kicker_irq);
45 atomic_t *nest_cnt = this_cpu_ptr(&xen_qlock_wait_nest);
46
47 /* If kicker interrupts not initialized yet, just spin */
48 if (irq == -1 || in_nmi())
49 return;
50
51 /* Detect reentry. */
52 atomic_inc(nest_cnt);
53
54 /* If irq pending already and no nested call clear it. */
55 if (atomic_read(nest_cnt) == 1 && xen_test_irq_pending(irq)) {
56 xen_clear_irq_pending(irq);
57 } else if (READ_ONCE(*byte) == val) {
58 /* Block until irq becomes pending (or a spurious wakeup) */
59 xen_poll_irq(irq);
60 }
61
62 atomic_dec(nest_cnt);
63 }
64
dummy_handler(int irq,void * dev_id)65 static irqreturn_t dummy_handler(int irq, void *dev_id)
66 {
67 BUG();
68 return IRQ_HANDLED;
69 }
70
xen_init_lock_cpu(int cpu)71 void xen_init_lock_cpu(int cpu)
72 {
73 int irq;
74 char *name;
75
76 if (!xen_pvspin) {
77 if (cpu == 0)
78 static_branch_disable(&virt_spin_lock_key);
79 return;
80 }
81
82 WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
83 cpu, per_cpu(lock_kicker_irq, cpu));
84
85 name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
86 irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
87 cpu,
88 dummy_handler,
89 IRQF_PERCPU|IRQF_NOBALANCING,
90 name,
91 NULL);
92
93 if (irq >= 0) {
94 disable_irq(irq); /* make sure it's never delivered */
95 per_cpu(lock_kicker_irq, cpu) = irq;
96 per_cpu(irq_name, cpu) = name;
97 }
98
99 printk("cpu %d spinlock event irq %d\n", cpu, irq);
100 }
101
xen_uninit_lock_cpu(int cpu)102 void xen_uninit_lock_cpu(int cpu)
103 {
104 if (!xen_pvspin)
105 return;
106
107 unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
108 per_cpu(lock_kicker_irq, cpu) = -1;
109 kfree(per_cpu(irq_name, cpu));
110 per_cpu(irq_name, cpu) = NULL;
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 */
xen_init_spinlocks(void)123 void __init xen_init_spinlocks(void)
124 {
125
126 /* Don't need to use pvqspinlock code if there is only 1 vCPU. */
127 if (num_possible_cpus() == 1)
128 xen_pvspin = false;
129
130 if (!xen_pvspin) {
131 printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
132 return;
133 }
134 printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
135
136 __pv_init_lock_hash();
137 pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
138 pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
139 pv_lock_ops.wait = xen_qlock_wait;
140 pv_lock_ops.kick = xen_qlock_kick;
141 pv_lock_ops.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen);
142 }
143
xen_parse_nopvspin(char * arg)144 static __init int xen_parse_nopvspin(char *arg)
145 {
146 xen_pvspin = false;
147 return 0;
148 }
149 early_param("xen_nopvspin", xen_parse_nopvspin);
150
151