On Fri, Jul 08, 2022 at 11:23:45AM +0000, Sebastian Ene wrote:
> This driver creates per-cpu hrtimers which are required to do the
> periodic 'pet' operation. On a conventional watchdog-core driver, the
> userspace is responsible for delivering the 'pet' events by writing to
> the particular /dev/watchdogN node. In this case we require a strong
> thread affinity to be able to account for lost time on a per vCPU.
>
> This part of the driver is the 'frontend' which is reponsible for
> delivering the periodic 'pet' events, configuring the virtual peripheral
> and listening for cpu hotplug events. The other part of the driver is
> an emulated MMIO device which is part of the KVM virtual machine
> monitor and this part accounts for lost time by looking at the
> /proc/{}/task/{}/stat entries.
>
> Reviewed-by: Will Deacon <will@xxxxxxxxxx>
> Signed-off-by: Sebastian Ene <sebastianene@xxxxxxxxxx>
Reviewed-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> ---
> drivers/misc/Kconfig | 14 ++
> drivers/misc/Makefile | 1 +
> drivers/misc/vcpu_stall_detector.c | 223 +++++++++++++++++++++++++++++
> 3 files changed, 238 insertions(+)
> create mode 100644 drivers/misc/vcpu_stall_detector.c
>
> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> index 41d2bb0ae23a..d5b7610459f7 100644
> --- a/drivers/misc/Kconfig
> +++ b/drivers/misc/Kconfig
> @@ -483,6 +483,20 @@ config OPEN_DICE
>
> If unsure, say N.
>
> +config VCPU_STALL_DETECTOR
> + tristate "Guest vCPU stall detector"
> + select LOCKUP_DETECTOR
> + depends on OF && HAS_IOMEM
> + help
> + When this driver is bound inside a KVM guest, it will
> + periodically "pet" an MMIO stall detector device from each vCPU
> + and allow the host to detect vCPU stalls.
> +
> + To compile this driver as a module, choose M here: the module
> + will be called vcpu_stall_detector.
> +
> + If you do not intend to run this kernel as a guest, say N.
> +
> source "drivers/misc/c2port/Kconfig"
> source "drivers/misc/eeprom/Kconfig"
> source "drivers/misc/cb710/Kconfig"
> diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
> index 70e800e9127f..2be8542616dd 100644
> --- a/drivers/misc/Makefile
> +++ b/drivers/misc/Makefile
> @@ -60,3 +60,4 @@ obj-$(CONFIG_XILINX_SDFEC) += xilinx_sdfec.o
> obj-$(CONFIG_HISI_HIKEY_USB) += hisi_hikey_usb.o
> obj-$(CONFIG_HI6421V600_IRQ) += hi6421v600-irq.o
> obj-$(CONFIG_OPEN_DICE) += open-dice.o
> +obj-$(CONFIG_VCPU_STALL_DETECTOR) += vcpu_stall_detector.o
> \ No newline at end of file
> diff --git a/drivers/misc/vcpu_stall_detector.c b/drivers/misc/vcpu_stall_detector.c
> new file mode 100644
> index 000000000000..53b5506080e1
> --- /dev/null
> +++ b/drivers/misc/vcpu_stall_detector.c
> @@ -0,0 +1,223 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +//
> +// VCPU stall detector.
> +// Copyright (C) Google, 2022
> +
> +#include <linux/cpu.h>
> +#include <linux/init.h>
> +#include <linux/io.h>
> +#include <linux/kernel.h>
> +
> +#include <linux/device.h>
> +#include <linux/interrupt.h>
> +#include <linux/module.h>
> +#include <linux/nmi.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/param.h>
> +#include <linux/percpu.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>
> +
> +#define VCPU_STALL_REG_STATUS (0x00)
> +#define VCPU_STALL_REG_LOAD_CNT (0x04)
> +#define VCPU_STALL_REG_CURRENT_CNT (0x08)
> +#define VCPU_STALL_REG_CLOCK_FREQ_HZ (0x0C)
> +#define VCPU_STALL_REG_LEN (0x10)
> +
> +#define VCPU_STALL_DEFAULT_CLOCK_HZ (10)
> +#define VCPU_STALL_MAX_CLOCK_HZ (100)
> +#define VCPU_STALL_DEFAULT_TIMEOUT_SEC (8)
> +#define VCPU_STALL_MAX_TIMEOUT_SEC (600)
> +
> +struct vcpu_stall_detect_config {
> + u32 clock_freq_hz;
> + u32 stall_timeout_sec;
> +
> + void __iomem *membase;
> + struct platform_device *dev;
> + enum cpuhp_state hp_online;
> +};
> +
> +struct vcpu_stall_priv {
> + struct hrtimer vcpu_hrtimer;
> + bool is_initialized;
> +};
> +
> +/* The vcpu stall configuration structure which applies to all the CPUs */
> +static struct vcpu_stall_detect_config vcpu_stall_config;
> +
> +#define vcpu_stall_reg_write(vcpu, reg, value) \
> + writel_relaxed((value), \
> + (void __iomem *)(vcpu_stall_config.membase + \
> + (vcpu) * VCPU_STALL_REG_LEN + (reg)))
> +
> +
> +static struct vcpu_stall_priv __percpu *vcpu_stall_detectors;
> +
> +static enum hrtimer_restart
> +vcpu_stall_detect_timer_fn(struct hrtimer *hrtimer)
> +{
> + u32 ticks, ping_timeout_ms;
> +
> + /* Reload the stall detector counter register every
> + * `ping_timeout_ms` to prevent the virtual device
> + * from decrementing it to 0. The virtual device decrements this
> + * register at 'clock_freq_hz' frequency.
> + */
> + ticks = vcpu_stall_config.clock_freq_hz *
> + vcpu_stall_config.stall_timeout_sec;
> + vcpu_stall_reg_write(smp_processor_id(),
> + VCPU_STALL_REG_LOAD_CNT, ticks);
> +
> + ping_timeout_ms = vcpu_stall_config.stall_timeout_sec *
> + MSEC_PER_SEC / 2;
> + hrtimer_forward_now(hrtimer,
> + ms_to_ktime(ping_timeout_ms));
> +
> + return HRTIMER_RESTART;
> +}
> +
> +static int start_stall_detector_cpu(unsigned int cpu)
> +{
> + u32 ticks, ping_timeout_ms;
> + struct vcpu_stall_priv *vcpu_stall_detector =
> + this_cpu_ptr(vcpu_stall_detectors);
> + struct hrtimer *vcpu_hrtimer = &vcpu_stall_detector->vcpu_hrtimer;
> +
> + vcpu_stall_reg_write(cpu, VCPU_STALL_REG_CLOCK_FREQ_HZ,
> + vcpu_stall_config.clock_freq_hz);
> +
> + /* Compute the number of ticks required for the stall detector
> + * counter register based on the internal clock frequency and the
> + * timeout value given from the device tree.
> + */
> + ticks = vcpu_stall_config.clock_freq_hz *
> + vcpu_stall_config.stall_timeout_sec;
> + vcpu_stall_reg_write(cpu, VCPU_STALL_REG_LOAD_CNT, ticks);
> +
> + /* Enable the internal clock and start the stall detector */
> + vcpu_stall_reg_write(cpu, VCPU_STALL_REG_STATUS, 1);
> +
> + /* Pet the stall detector at half of its expiration timeout
> + * to prevent spurious resets.
> + */
> + ping_timeout_ms = vcpu_stall_config.stall_timeout_sec *
> + MSEC_PER_SEC / 2;
> +
> + hrtimer_init(vcpu_hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> + vcpu_hrtimer->function = vcpu_stall_detect_timer_fn;
> + vcpu_stall_detector->is_initialized = true;
> +
> + hrtimer_start(vcpu_hrtimer, ms_to_ktime(ping_timeout_ms),
> + HRTIMER_MODE_REL_PINNED);
> +
> + return 0;
> +}
> +
> +static int stop_stall_detector_cpu(unsigned int cpu)
> +{
> + struct vcpu_stall_priv *vcpu_stall_detector =
> + per_cpu_ptr(vcpu_stall_detectors, cpu);
> +
> + if (!vcpu_stall_detector->is_initialized)
> + return 0;
> +
> + /* Disable the stall detector for the current CPU */
> + hrtimer_cancel(&vcpu_stall_detector->vcpu_hrtimer);
> + vcpu_stall_reg_write(cpu, VCPU_STALL_REG_STATUS, 0);
> + vcpu_stall_detector->is_initialized = false;
> +
> + return 0;
> +}
> +
> +static int vcpu_stall_detect_probe(struct platform_device *pdev)
> +{
> + int ret;
> + struct resource *r;
> + void __iomem *membase;
> + u32 clock_freq_hz = VCPU_STALL_DEFAULT_CLOCK_HZ;
> + u32 stall_timeout_sec = VCPU_STALL_DEFAULT_TIMEOUT_SEC;
> + struct device_node *np = pdev->dev.of_node;
> +
> + vcpu_stall_detectors = devm_alloc_percpu(&pdev->dev,
> + typeof(struct vcpu_stall_priv));
> + if (!vcpu_stall_detectors)
> + return -ENOMEM;
> +
> + membase = devm_platform_get_and_ioremap_resource(pdev, 0, &r);
> + if (IS_ERR(membase)) {
> + dev_err(&pdev->dev, "Failed to get memory resource\n");
> + return PTR_ERR(membase);
> + }
> +
> + if (!of_property_read_u32(np, "clock-frequency", &clock_freq_hz)) {
> + if (!(clock_freq_hz > 0 &&
> + clock_freq_hz < VCPU_STALL_MAX_CLOCK_HZ)) {
> + dev_warn(&pdev->dev, "clk out of range\n");
> + clock_freq_hz = VCPU_STALL_DEFAULT_CLOCK_HZ;
> + }
> + }
> +
> + if (!of_property_read_u32(np, "timeout-sec", &stall_timeout_sec)) {
> + if (!(stall_timeout_sec > 0 &&
> + stall_timeout_sec < VCPU_STALL_MAX_TIMEOUT_SEC)) {
> + dev_warn(&pdev->dev, "stall timeout out of range\n");
> + stall_timeout_sec = VCPU_STALL_DEFAULT_TIMEOUT_SEC;
> + }
> + }
> +
> + vcpu_stall_config = (struct vcpu_stall_detect_config) {
> + .membase = membase,
> + .clock_freq_hz = clock_freq_hz,
> + .stall_timeout_sec = stall_timeout_sec
> + };
> +
> + ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
> + "virt/vcpu_stall_detector:online",
> + start_stall_detector_cpu,
> + stop_stall_detector_cpu);
> + if (ret < 0) {
> + dev_err(&pdev->dev, "failed to install cpu hotplug");
> + goto err;
> + }
> +
> + vcpu_stall_config.hp_online = ret;
> + return 0;
> +err:
> + return ret;
> +}
> +
> +static int vcpu_stall_detect_remove(struct platform_device *pdev)
> +{
> + int cpu;
> +
> + cpuhp_remove_state(vcpu_stall_config.hp_online);
> +
> + for_each_possible_cpu(cpu)
> + stop_stall_detector_cpu(cpu);
> +
> + return 0;
> +}
> +
> +static const struct of_device_id vcpu_stall_detect_of_match[] = {
> + { .compatible = "qemu,vcpu-stall-detector", },
> + {}
> +};
> +
> +MODULE_DEVICE_TABLE(of, vcpu_stall_detect_of_match);
> +
> +static struct platform_driver vcpu_stall_detect_driver = {
> + .probe = vcpu_stall_detect_probe,
> + .remove = vcpu_stall_detect_remove,
> + .driver = {
> + .name = KBUILD_MODNAME,
> + .of_match_table = vcpu_stall_detect_of_match,
> + },
> +};
> +
> +module_platform_driver(vcpu_stall_detect_driver);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Sebastian Ene <sebastianene@xxxxxxxxxx>");
> +MODULE_DESCRIPTION("VCPU stall detector");
> --
> 2.37.0.rc0.161.g10f37bed90-goog
>
