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
 36	void __iomem *membase;
 37	struct platform_device *dev;
 38	enum cpuhp_state hp_online;
 39};
 40
 41struct 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 */
 47static 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
 55static struct vcpu_stall_priv __percpu *vcpu_stall_detectors;
 56
 57static enum hrtimer_restart
 58vcpu_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
 80static 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
117static 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
133static 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;
186err:
187	return ret;
188}
189
190static 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
202static const struct of_device_id vcpu_stall_detect_of_match[] = {
203	{ .compatible = "qemu,vcpu-stall-detector", },
204	{}
205};
206
207MODULE_DEVICE_TABLE(of, vcpu_stall_detect_of_match);
208
209static 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
218module_platform_driver(vcpu_stall_detect_driver);
219
220MODULE_LICENSE("GPL");
221MODULE_AUTHOR("Sebastian Ene <sebastianene@google.com>");
222MODULE_DESCRIPTION("VCPU stall detector");