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/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");