drivers/misc/vcpu_stall_detector.c

   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
  33 struct 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
  42 struct 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 */
  48 static 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
  56 static struct vcpu_stall_priv __percpu *vcpu_stall_detectors;
  57
  58 static enum hrtimer_restart
  59 vcpu_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
  81 static 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
 118 static 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
 134 static 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;
 187 err:
 188         return ret;
 189 }
 190
 191 static 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
 203 static const struct of_device_id vcpu_stall_detect_of_match[] = {
 204         { .compatible = "qemu,vcpu-stall-detector", },
 205         {}
 206 };
 207
 208 MODULE_DEVICE_TABLE(of, vcpu_stall_detect_of_match);
 209
 210 static 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
 219 module_platform_driver(vcpu_stall_detect_driver);
 220
 221 MODULE_LICENSE("GPL");
 222 MODULE_AUTHOR("Sebastian Ene <sebastianene@google.com>");
 223 MODULE_DESCRIPTION("VCPU stall detector");