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1// SPDX-License-Identifier: GPL-2.0-only
2//
3// VCPU stall detector.
4// Copyright (C) Google, 2022
5
6#include <linux/cpu.h>
7#include <linux/init.h>
8#include <linux/io.h>
9#include <linux/kernel.h>
10
11#include <linux/device.h>
12#include <linux/interrupt.h>
13#include <linux/module.h>
14#include <linux/nmi.h>
15#include <linux/of.h>
16#include <linux/param.h>
17#include <linux/percpu.h>
18#include <linux/platform_device.h>
19#include <linux/slab.h>
20
21#define VCPU_STALL_REG_STATUS (0x00)
22#define VCPU_STALL_REG_LOAD_CNT (0x04)
23#define VCPU_STALL_REG_CURRENT_CNT (0x08)
24#define VCPU_STALL_REG_CLOCK_FREQ_HZ (0x0C)
25#define VCPU_STALL_REG_LEN (0x10)
26
27#define VCPU_STALL_DEFAULT_CLOCK_HZ (10)
28#define VCPU_STALL_MAX_CLOCK_HZ (100)
29#define VCPU_STALL_DEFAULT_TIMEOUT_SEC (8)
30#define VCPU_STALL_MAX_TIMEOUT_SEC (600)
31
32struct vcpu_stall_detect_config {
33 u32 clock_freq_hz;
34 u32 stall_timeout_sec;
35 int ppi_irq;
36
37 void __iomem *membase;
38 struct platform_device *dev;
39 enum cpuhp_state hp_online;
40};
41
42struct vcpu_stall_priv {
43 struct hrtimer vcpu_hrtimer;
44 bool is_initialized;
45};
46
47/* The vcpu stall configuration structure which applies to all the CPUs */
48static struct vcpu_stall_detect_config vcpu_stall_config;
49
50#define vcpu_stall_reg_write(vcpu, reg, value) \
51 writel_relaxed((value), \
52 (void __iomem *)(vcpu_stall_config.membase + \
53 (vcpu) * VCPU_STALL_REG_LEN + (reg)))
54
55
56static struct vcpu_stall_priv __percpu *vcpu_stall_detectors;
57
58static enum hrtimer_restart
59vcpu_stall_detect_timer_fn(struct hrtimer *hrtimer)
60{
61 u32 ticks, ping_timeout_ms;
62
63 /* Reload the stall detector counter register every
64 * `ping_timeout_ms` to prevent the virtual device
65 * from decrementing it to 0. The virtual device decrements this
66 * register at 'clock_freq_hz' frequency.
67 */
68 ticks = vcpu_stall_config.clock_freq_hz *
69 vcpu_stall_config.stall_timeout_sec;
70 vcpu_stall_reg_write(smp_processor_id(),
71 VCPU_STALL_REG_LOAD_CNT, ticks);
72
73 ping_timeout_ms = vcpu_stall_config.stall_timeout_sec *
74 MSEC_PER_SEC / 2;
75 hrtimer_forward_now(hrtimer,
76 ms_to_ktime(ping_timeout_ms));
77
78 return HRTIMER_RESTART;
79}
80
81static irqreturn_t vcpu_stall_detector_irq(int irq, void *dev)
82{
83 panic("vCPU stall detector");
84 return IRQ_HANDLED;
85}
86
87static int start_stall_detector_cpu(unsigned int cpu)
88{
89 u32 ticks, ping_timeout_ms;
90 struct vcpu_stall_priv *vcpu_stall_detector =
91 this_cpu_ptr(vcpu_stall_detectors);
92 struct hrtimer *vcpu_hrtimer = &vcpu_stall_detector->vcpu_hrtimer;
93
94 vcpu_stall_reg_write(cpu, VCPU_STALL_REG_CLOCK_FREQ_HZ,
95 vcpu_stall_config.clock_freq_hz);
96
97 /* Compute the number of ticks required for the stall detector
98 * counter register based on the internal clock frequency and the
99 * timeout value given from the device tree.
100 */
101 ticks = vcpu_stall_config.clock_freq_hz *
102 vcpu_stall_config.stall_timeout_sec;
103 vcpu_stall_reg_write(cpu, VCPU_STALL_REG_LOAD_CNT, ticks);
104
105 /* Enable the internal clock and start the stall detector */
106 vcpu_stall_reg_write(cpu, VCPU_STALL_REG_STATUS, 1);
107
108 /* Pet the stall detector at half of its expiration timeout
109 * to prevent spurious resets.
110 */
111 ping_timeout_ms = vcpu_stall_config.stall_timeout_sec *
112 MSEC_PER_SEC / 2;
113
114 hrtimer_setup(vcpu_hrtimer, vcpu_stall_detect_timer_fn, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
115 vcpu_stall_detector->is_initialized = true;
116
117 hrtimer_start(vcpu_hrtimer, ms_to_ktime(ping_timeout_ms),
118 HRTIMER_MODE_REL_PINNED);
119
120 return 0;
121}
122
123static int stop_stall_detector_cpu(unsigned int cpu)
124{
125 struct vcpu_stall_priv *vcpu_stall_detector =
126 per_cpu_ptr(vcpu_stall_detectors, cpu);
127
128 if (!vcpu_stall_detector->is_initialized)
129 return 0;
130
131 /* Disable the stall detector for the current CPU */
132 hrtimer_cancel(&vcpu_stall_detector->vcpu_hrtimer);
133 vcpu_stall_reg_write(cpu, VCPU_STALL_REG_STATUS, 0);
134 vcpu_stall_detector->is_initialized = false;
135
136 return 0;
137}
138
139static int vcpu_stall_detect_probe(struct platform_device *pdev)
140{
141 int ret, irq;
142 struct resource *r;
143 void __iomem *membase;
144 u32 clock_freq_hz = VCPU_STALL_DEFAULT_CLOCK_HZ;
145 u32 stall_timeout_sec = VCPU_STALL_DEFAULT_TIMEOUT_SEC;
146 struct device_node *np = pdev->dev.of_node;
147
148 vcpu_stall_detectors = devm_alloc_percpu(&pdev->dev,
149 typeof(struct vcpu_stall_priv));
150 if (!vcpu_stall_detectors)
151 return -ENOMEM;
152
153 membase = devm_platform_get_and_ioremap_resource(pdev, 0, &r);
154 if (IS_ERR(membase)) {
155 dev_err(&pdev->dev, "Failed to get memory resource\n");
156 return PTR_ERR(membase);
157 }
158
159 if (!of_property_read_u32(np, "clock-frequency", &clock_freq_hz)) {
160 if (!(clock_freq_hz > 0 &&
161 clock_freq_hz < VCPU_STALL_MAX_CLOCK_HZ)) {
162 dev_warn(&pdev->dev, "clk out of range\n");
163 clock_freq_hz = VCPU_STALL_DEFAULT_CLOCK_HZ;
164 }
165 }
166
167 if (!of_property_read_u32(np, "timeout-sec", &stall_timeout_sec)) {
168 if (!(stall_timeout_sec > 0 &&
169 stall_timeout_sec < VCPU_STALL_MAX_TIMEOUT_SEC)) {
170 dev_warn(&pdev->dev, "stall timeout out of range\n");
171 stall_timeout_sec = VCPU_STALL_DEFAULT_TIMEOUT_SEC;
172 }
173 }
174
175 vcpu_stall_config = (struct vcpu_stall_detect_config) {
176 .membase = membase,
177 .clock_freq_hz = clock_freq_hz,
178 .stall_timeout_sec = stall_timeout_sec,
179 .ppi_irq = -1,
180 };
181
182 irq = platform_get_irq_optional(pdev, 0);
183 if (irq > 0) {
184 ret = request_percpu_irq(irq,
185 vcpu_stall_detector_irq,
186 "vcpu_stall_detector",
187 vcpu_stall_detectors);
188 if (ret)
189 goto err;
190
191 vcpu_stall_config.ppi_irq = irq;
192 }
193
194 ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
195 "virt/vcpu_stall_detector:online",
196 start_stall_detector_cpu,
197 stop_stall_detector_cpu);
198 if (ret < 0) {
199 dev_err(&pdev->dev, "failed to install cpu hotplug");
200 goto err;
201 }
202
203 vcpu_stall_config.hp_online = ret;
204 return 0;
205err:
206 if (vcpu_stall_config.ppi_irq > 0)
207 free_percpu_irq(vcpu_stall_config.ppi_irq,
208 vcpu_stall_detectors);
209 return ret;
210}
211
212static void vcpu_stall_detect_remove(struct platform_device *pdev)
213{
214 int cpu;
215
216 cpuhp_remove_state(vcpu_stall_config.hp_online);
217
218 if (vcpu_stall_config.ppi_irq > 0)
219 free_percpu_irq(vcpu_stall_config.ppi_irq,
220 vcpu_stall_detectors);
221
222 for_each_possible_cpu(cpu)
223 stop_stall_detector_cpu(cpu);
224}
225
226static const struct of_device_id vcpu_stall_detect_of_match[] = {
227 { .compatible = "qemu,vcpu-stall-detector" },
228 { }
229};
230
231MODULE_DEVICE_TABLE(of, vcpu_stall_detect_of_match);
232
233static struct platform_driver vcpu_stall_detect_driver = {
234 .probe = vcpu_stall_detect_probe,
235 .remove = vcpu_stall_detect_remove,
236 .driver = {
237 .name = KBUILD_MODNAME,
238 .of_match_table = vcpu_stall_detect_of_match,
239 },
240};
241
242module_platform_driver(vcpu_stall_detect_driver);
243
244MODULE_LICENSE("GPL");
245MODULE_AUTHOR("Sebastian Ene <[email protected]>");
246MODULE_DESCRIPTION("VCPU stall detector");