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/of_device.h>
 17#include <linux/param.h>
 18#include <linux/percpu.h>
 19#include <linux/platform_device.h>
 20#include <linux/slab.h>
 21
 22#define VCPU_STALL_REG_STATUS		(0x00)
 23#define VCPU_STALL_REG_LOAD_CNT		(0x04)
 24#define VCPU_STALL_REG_CURRENT_CNT	(0x08)
 25#define VCPU_STALL_REG_CLOCK_FREQ_HZ	(0x0C)
 26#define VCPU_STALL_REG_LEN		(0x10)
 27
 28#define VCPU_STALL_DEFAULT_CLOCK_HZ	(10)
 29#define VCPU_STALL_MAX_CLOCK_HZ		(100)
 30#define VCPU_STALL_DEFAULT_TIMEOUT_SEC	(8)
 31#define VCPU_STALL_MAX_TIMEOUT_SEC	(600)
 32
 33struct vcpu_stall_detect_config {
 34	u32 clock_freq_hz;
 35	u32 stall_timeout_sec;
 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 int start_stall_detector_cpu(unsigned int cpu)
 82{
 83	u32 ticks, ping_timeout_ms;
 84	struct vcpu_stall_priv *vcpu_stall_detector =
 85		this_cpu_ptr(vcpu_stall_detectors);
 86	struct hrtimer *vcpu_hrtimer = &vcpu_stall_detector->vcpu_hrtimer;
 87
 88	vcpu_stall_reg_write(cpu, VCPU_STALL_REG_CLOCK_FREQ_HZ,
 89			     vcpu_stall_config.clock_freq_hz);
 90
 91	/* Compute the number of ticks required for the stall detector
 92	 * counter register based on the internal clock frequency and the
 93	 * timeout value given from the device tree.
 94	 */
 95	ticks = vcpu_stall_config.clock_freq_hz *
 96		vcpu_stall_config.stall_timeout_sec;
 97	vcpu_stall_reg_write(cpu, VCPU_STALL_REG_LOAD_CNT, ticks);
 98
 99	/* Enable the internal clock and start the stall detector */
100	vcpu_stall_reg_write(cpu, VCPU_STALL_REG_STATUS, 1);
101
102	/* Pet the stall detector at half of its expiration timeout
103	 * to prevent spurious resets.
104	 */
105	ping_timeout_ms = vcpu_stall_config.stall_timeout_sec *
106			  MSEC_PER_SEC / 2;
107
108	hrtimer_init(vcpu_hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
109	vcpu_hrtimer->function = vcpu_stall_detect_timer_fn;
110	vcpu_stall_detector->is_initialized = true;
111
112	hrtimer_start(vcpu_hrtimer, ms_to_ktime(ping_timeout_ms),
113		      HRTIMER_MODE_REL_PINNED);
114
115	return 0;
116}
117
118static int stop_stall_detector_cpu(unsigned int cpu)
119{
120	struct vcpu_stall_priv *vcpu_stall_detector =
121		per_cpu_ptr(vcpu_stall_detectors, cpu);
122
123	if (!vcpu_stall_detector->is_initialized)
124		return 0;
125
126	/* Disable the stall detector for the current CPU */
127	hrtimer_cancel(&vcpu_stall_detector->vcpu_hrtimer);
128	vcpu_stall_reg_write(cpu, VCPU_STALL_REG_STATUS, 0);
129	vcpu_stall_detector->is_initialized = false;
130
131	return 0;
132}
133
134static int vcpu_stall_detect_probe(struct platform_device *pdev)
135{
136	int ret;
137	struct resource *r;
138	void __iomem *membase;
139	u32 clock_freq_hz = VCPU_STALL_DEFAULT_CLOCK_HZ;
140	u32 stall_timeout_sec = VCPU_STALL_DEFAULT_TIMEOUT_SEC;
141	struct device_node *np = pdev->dev.of_node;
142
143	vcpu_stall_detectors = devm_alloc_percpu(&pdev->dev,
144						 typeof(struct vcpu_stall_priv));
145	if (!vcpu_stall_detectors)
146		return -ENOMEM;
147
148	membase = devm_platform_get_and_ioremap_resource(pdev, 0, &r);
149	if (IS_ERR(membase)) {
150		dev_err(&pdev->dev, "Failed to get memory resource\n");
151		return PTR_ERR(membase);
152	}
153
154	if (!of_property_read_u32(np, "clock-frequency", &clock_freq_hz)) {
155		if (!(clock_freq_hz > 0 &&
156		      clock_freq_hz < VCPU_STALL_MAX_CLOCK_HZ)) {
157			dev_warn(&pdev->dev, "clk out of range\n");
158			clock_freq_hz = VCPU_STALL_DEFAULT_CLOCK_HZ;
159		}
160	}
161
162	if (!of_property_read_u32(np, "timeout-sec", &stall_timeout_sec)) {
163		if (!(stall_timeout_sec > 0 &&
164		      stall_timeout_sec < VCPU_STALL_MAX_TIMEOUT_SEC)) {
165			dev_warn(&pdev->dev, "stall timeout out of range\n");
166			stall_timeout_sec = VCPU_STALL_DEFAULT_TIMEOUT_SEC;
167		}
168	}
169
170	vcpu_stall_config = (struct vcpu_stall_detect_config) {
171		.membase		= membase,
172		.clock_freq_hz		= clock_freq_hz,
173		.stall_timeout_sec	= stall_timeout_sec
174	};
175
176	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
177				"virt/vcpu_stall_detector:online",
178				start_stall_detector_cpu,
179				stop_stall_detector_cpu);
180	if (ret < 0) {
181		dev_err(&pdev->dev, "failed to install cpu hotplug");
182		goto err;
183	}
184
185	vcpu_stall_config.hp_online = ret;
186	return 0;
187err:
188	return ret;
189}
190
191static int vcpu_stall_detect_remove(struct platform_device *pdev)
192{
193	int cpu;
194
195	cpuhp_remove_state(vcpu_stall_config.hp_online);
196
197	for_each_possible_cpu(cpu)
198		stop_stall_detector_cpu(cpu);
199
200	return 0;
201}
202
203static const struct of_device_id vcpu_stall_detect_of_match[] = {
204	{ .compatible = "qemu,vcpu-stall-detector", },
205	{}
206};
207
208MODULE_DEVICE_TABLE(of, vcpu_stall_detect_of_match);
209
210static struct platform_driver vcpu_stall_detect_driver = {
211	.probe  = vcpu_stall_detect_probe,
212	.remove = vcpu_stall_detect_remove,
213	.driver = {
214		.name           = KBUILD_MODNAME,
215		.of_match_table = vcpu_stall_detect_of_match,
216	},
217};
218
219module_platform_driver(vcpu_stall_detect_driver);
220
221MODULE_LICENSE("GPL");
222MODULE_AUTHOR("Sebastian Ene <sebastianene@google.com>");
223MODULE_DESCRIPTION("VCPU stall detector");