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 
32 struct vcpu_stall_detect_config {
33 	u32 clock_freq_hz;
34 	u32 stall_timeout_sec;
35 
36 	void __iomem *membase;
37 	struct platform_device *dev;
38 	enum cpuhp_state hp_online;
39 };
40 
41 struct vcpu_stall_priv {
42 	struct hrtimer vcpu_hrtimer;
43 	bool is_initialized;
44 };
45 
46 /* The vcpu stall configuration structure which applies to all the CPUs */
47 static struct vcpu_stall_detect_config vcpu_stall_config;
48 
49 #define vcpu_stall_reg_write(vcpu, reg, value)				\
50 	writel_relaxed((value),						\
51 		       (void __iomem *)(vcpu_stall_config.membase +	\
52 		       (vcpu) * VCPU_STALL_REG_LEN + (reg)))
53 
54 
55 static struct vcpu_stall_priv __percpu *vcpu_stall_detectors;
56 
57 static enum hrtimer_restart
58 vcpu_stall_detect_timer_fn(struct hrtimer *hrtimer)
59 {
60 	u32 ticks, ping_timeout_ms;
61 
62 	/* Reload the stall detector counter register every
63 	 * `ping_timeout_ms` to prevent the virtual device
64 	 * from decrementing it to 0. The virtual device decrements this
65 	 * register at 'clock_freq_hz' frequency.
66 	 */
67 	ticks = vcpu_stall_config.clock_freq_hz *
68 		vcpu_stall_config.stall_timeout_sec;
69 	vcpu_stall_reg_write(smp_processor_id(),
70 			     VCPU_STALL_REG_LOAD_CNT, ticks);
71 
72 	ping_timeout_ms = vcpu_stall_config.stall_timeout_sec *
73 			  MSEC_PER_SEC / 2;
74 	hrtimer_forward_now(hrtimer,
75 			    ms_to_ktime(ping_timeout_ms));
76 
77 	return HRTIMER_RESTART;
78 }
79 
80 static int start_stall_detector_cpu(unsigned int cpu)
81 {
82 	u32 ticks, ping_timeout_ms;
83 	struct vcpu_stall_priv *vcpu_stall_detector =
84 		this_cpu_ptr(vcpu_stall_detectors);
85 	struct hrtimer *vcpu_hrtimer = &vcpu_stall_detector->vcpu_hrtimer;
86 
87 	vcpu_stall_reg_write(cpu, VCPU_STALL_REG_CLOCK_FREQ_HZ,
88 			     vcpu_stall_config.clock_freq_hz);
89 
90 	/* Compute the number of ticks required for the stall detector
91 	 * counter register based on the internal clock frequency and the
92 	 * timeout value given from the device tree.
93 	 */
94 	ticks = vcpu_stall_config.clock_freq_hz *
95 		vcpu_stall_config.stall_timeout_sec;
96 	vcpu_stall_reg_write(cpu, VCPU_STALL_REG_LOAD_CNT, ticks);
97 
98 	/* Enable the internal clock and start the stall detector */
99 	vcpu_stall_reg_write(cpu, VCPU_STALL_REG_STATUS, 1);
100 
101 	/* Pet the stall detector at half of its expiration timeout
102 	 * to prevent spurious resets.
103 	 */
104 	ping_timeout_ms = vcpu_stall_config.stall_timeout_sec *
105 			  MSEC_PER_SEC / 2;
106 
107 	hrtimer_init(vcpu_hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
108 	vcpu_hrtimer->function = vcpu_stall_detect_timer_fn;
109 	vcpu_stall_detector->is_initialized = true;
110 
111 	hrtimer_start(vcpu_hrtimer, ms_to_ktime(ping_timeout_ms),
112 		      HRTIMER_MODE_REL_PINNED);
113 
114 	return 0;
115 }
116 
117 static int stop_stall_detector_cpu(unsigned int cpu)
118 {
119 	struct vcpu_stall_priv *vcpu_stall_detector =
120 		per_cpu_ptr(vcpu_stall_detectors, cpu);
121 
122 	if (!vcpu_stall_detector->is_initialized)
123 		return 0;
124 
125 	/* Disable the stall detector for the current CPU */
126 	hrtimer_cancel(&vcpu_stall_detector->vcpu_hrtimer);
127 	vcpu_stall_reg_write(cpu, VCPU_STALL_REG_STATUS, 0);
128 	vcpu_stall_detector->is_initialized = false;
129 
130 	return 0;
131 }
132 
133 static int vcpu_stall_detect_probe(struct platform_device *pdev)
134 {
135 	int ret;
136 	struct resource *r;
137 	void __iomem *membase;
138 	u32 clock_freq_hz = VCPU_STALL_DEFAULT_CLOCK_HZ;
139 	u32 stall_timeout_sec = VCPU_STALL_DEFAULT_TIMEOUT_SEC;
140 	struct device_node *np = pdev->dev.of_node;
141 
142 	vcpu_stall_detectors = devm_alloc_percpu(&pdev->dev,
143 						 typeof(struct vcpu_stall_priv));
144 	if (!vcpu_stall_detectors)
145 		return -ENOMEM;
146 
147 	membase = devm_platform_get_and_ioremap_resource(pdev, 0, &r);
148 	if (IS_ERR(membase)) {
149 		dev_err(&pdev->dev, "Failed to get memory resource\n");
150 		return PTR_ERR(membase);
151 	}
152 
153 	if (!of_property_read_u32(np, "clock-frequency", &clock_freq_hz)) {
154 		if (!(clock_freq_hz > 0 &&
155 		      clock_freq_hz < VCPU_STALL_MAX_CLOCK_HZ)) {
156 			dev_warn(&pdev->dev, "clk out of range\n");
157 			clock_freq_hz = VCPU_STALL_DEFAULT_CLOCK_HZ;
158 		}
159 	}
160 
161 	if (!of_property_read_u32(np, "timeout-sec", &stall_timeout_sec)) {
162 		if (!(stall_timeout_sec > 0 &&
163 		      stall_timeout_sec < VCPU_STALL_MAX_TIMEOUT_SEC)) {
164 			dev_warn(&pdev->dev, "stall timeout out of range\n");
165 			stall_timeout_sec = VCPU_STALL_DEFAULT_TIMEOUT_SEC;
166 		}
167 	}
168 
169 	vcpu_stall_config = (struct vcpu_stall_detect_config) {
170 		.membase		= membase,
171 		.clock_freq_hz		= clock_freq_hz,
172 		.stall_timeout_sec	= stall_timeout_sec
173 	};
174 
175 	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
176 				"virt/vcpu_stall_detector:online",
177 				start_stall_detector_cpu,
178 				stop_stall_detector_cpu);
179 	if (ret < 0) {
180 		dev_err(&pdev->dev, "failed to install cpu hotplug");
181 		goto err;
182 	}
183 
184 	vcpu_stall_config.hp_online = ret;
185 	return 0;
186 err:
187 	return ret;
188 }
189 
190 static int vcpu_stall_detect_remove(struct platform_device *pdev)
191 {
192 	int cpu;
193 
194 	cpuhp_remove_state(vcpu_stall_config.hp_online);
195 
196 	for_each_possible_cpu(cpu)
197 		stop_stall_detector_cpu(cpu);
198 
199 	return 0;
200 }
201 
202 static const struct of_device_id vcpu_stall_detect_of_match[] = {
203 	{ .compatible = "qemu,vcpu-stall-detector", },
204 	{}
205 };
206 
207 MODULE_DEVICE_TABLE(of, vcpu_stall_detect_of_match);
208 
209 static struct platform_driver vcpu_stall_detect_driver = {
210 	.probe  = vcpu_stall_detect_probe,
211 	.remove = vcpu_stall_detect_remove,
212 	.driver = {
213 		.name           = KBUILD_MODNAME,
214 		.of_match_table = vcpu_stall_detect_of_match,
215 	},
216 };
217 
218 module_platform_driver(vcpu_stall_detect_driver);
219 
220 MODULE_LICENSE("GPL");
221 MODULE_AUTHOR("Sebastian Ene <sebastianene@google.com>");
222 MODULE_DESCRIPTION("VCPU stall detector");
223