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Date:   Fri, 29 Apr 2022 08:30:33 +0000
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Subject: [PATCH v4 2/2] misc: Add a mechanism to detect stalls on guest vCPUs
From:   Sebastian Ene <sebastianene@google.com>
To:     Rob Herring <robh+dt@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Dragan Cvetic <dragan.cvetic@xilinx.com>
Cc:     linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
        maz@kernel.org, will@kernel.org, qperret@google.com,
        Guenter Roeck <linux@roeck-us.net>,
        Sebastian Ene <sebastianene@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

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
handles the peripheral emulation and this part accounts for lost time by
looking at the /proc/{}/task/{}/stat entries and is located here:
https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3548817

Signed-off-by: Sebastian Ene <sebastianene@google.com>
---
 drivers/misc/Kconfig       |  12 +++
 drivers/misc/Makefile      |   1 +
 drivers/misc/vm-watchdog.c | 206 +++++++++++++++++++++++++++++++++++++
 3 files changed, 219 insertions(+)
 create mode 100644 drivers/misc/vm-watchdog.c

diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index 2b9572a6d114..26c3a99e269c 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -493,6 +493,18 @@ config OPEN_DICE
 
 	  If unsure, say N.
 
+config VM_WATCHDOG
+	tristate "Virtual Machine Watchdog"
+	select LOCKUP_DETECTOR
+	help
+	  Detect CPU locks on the virtual machine. This driver relies on the
+	  hrtimers which are CPU-binded to do the 'pet' operation. When a vCPU
+	  has to do a 'pet', it exits the guest through MMIO write and the
+	  backend driver takes into account the lost ticks for this particular
+	  CPU.
+	  To compile this driver as a module, choose M here: the
+	  module will be called vm-wdt.
+
 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 2ec634354cf5..9ea562d0c98b 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -59,3 +59,4 @@ obj-$(CONFIG_XILINX_SDFEC)	+= xilinx_sdfec.o
 obj-$(CONFIG_HISI_HIKEY_USB)	+= hisi_hikey_usb.o
 obj-$(CONFIG_UID_SYS_STATS)	+= uid_sys_stats.o
 obj-$(CONFIG_OPEN_DICE)		+= open-dice.o
+obj-$(CONFIG_VM_WATCHDOG)	+= vm-watchdog.o
\ No newline at end of file
diff --git a/drivers/misc/vm-watchdog.c b/drivers/misc/vm-watchdog.c
new file mode 100644
index 000000000000..1d344e9a84a8
--- /dev/null
+++ b/drivers/misc/vm-watchdog.c
@@ -0,0 +1,206 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Virtual watchdog driver.
+//  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 VMWDT_REG_STATUS		(0x00)
+#define VMWDT_REG_LOAD_CNT		(0x04)
+#define VMWDT_REG_CURRENT_CNT		(0x08)
+#define VMWDT_REG_CLOCK_FREQ_HZ		(0x0C)
+#define VMWDT_REG_LEN			(0x10)
+
+#define VMWDT_DEFAULT_CLOCK_HZ		(10)
+#define VMWDT_DEFAULT_TIMEOT_SEC	(8)
+
+struct vm_wdt_s {
+	void __iomem *membase;
+	u32 clock_freq;
+	u32 expiration_sec;
+	u32 ping_timeout_ms;
+	struct hrtimer per_cpu_hrtimer;
+	struct platform_device *dev;
+};
+
+#define vmwdt_reg_write(wdt, reg, value)	\
+	iowrite32((value), (wdt)->membase + (reg))
+#define vmwdt_reg_read(wdt, reg)		\
+	io32read((wdt)->membase + (reg))
+
+static struct platform_device *virt_dev;
+
+static enum hrtimer_restart vmwdt_timer_fn(struct hrtimer *hrtimer)
+{
+	struct vm_wdt_s *cpu_wdt;
+	u32 ticks;
+
+	cpu_wdt = container_of(hrtimer, struct vm_wdt_s, per_cpu_hrtimer);
+	ticks = cpu_wdt->clock_freq * cpu_wdt->expiration_sec;
+	vmwdt_reg_write(cpu_wdt, VMWDT_REG_LOAD_CNT, ticks);
+	hrtimer_forward_now(hrtimer, ms_to_ktime(cpu_wdt->ping_timeout_ms));
+
+	return HRTIMER_RESTART;
+}
+
+static void vmwdt_start(void *arg)
+{
+	u32 ticks;
+	struct vm_wdt_s *cpu_wdt = arg;
+	struct hrtimer *hrtimer = &cpu_wdt->per_cpu_hrtimer;
+
+	vmwdt_reg_write(cpu_wdt, VMWDT_REG_CLOCK_FREQ_HZ,
+			cpu_wdt->clock_freq);
+
+	/* Compute the number of ticks required for the watchdog counter
+	 * register based on the internal clock frequency and the watchdog
+	 * timeout given from the device tree.
+	 */
+	ticks = cpu_wdt->clock_freq * cpu_wdt->expiration_sec;
+	vmwdt_reg_write(cpu_wdt, VMWDT_REG_LOAD_CNT, ticks);
+
+	/* Enable the internal clock and start the watchdog */
+	vmwdt_reg_write(cpu_wdt, VMWDT_REG_STATUS, 1);
+
+	hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	hrtimer->function = vmwdt_timer_fn;
+	hrtimer_start(hrtimer, ms_to_ktime(cpu_wdt->ping_timeout_ms),
+		      HRTIMER_MODE_REL_PINNED);
+}
+
+static void vmwdt_stop(void *arg)
+{
+	struct vm_wdt_s *cpu_wdt = arg;
+	struct hrtimer *hrtimer = &cpu_wdt->per_cpu_hrtimer;
+
+	hrtimer_cancel(hrtimer);
+
+	/* Disable the watchdog */
+	vmwdt_reg_write(cpu_wdt, VMWDT_REG_STATUS, 0);
+}
+
+static int start_watchdog_on_cpu(unsigned int cpu)
+{
+	struct vm_wdt_s *vm_wdt = platform_get_drvdata(virt_dev);
+
+	vmwdt_start(this_cpu_ptr(vm_wdt));
+	return 0;
+}
+
+static int stop_watchdog_on_cpu(unsigned int cpu)
+{
+	struct vm_wdt_s *vm_wdt = platform_get_drvdata(virt_dev);
+
+	vmwdt_stop(this_cpu_ptr(vm_wdt));
+	return 0;
+}
+
+static int vmwdt_probe(struct platform_device *dev)
+{
+	int cpu, ret, err;
+	void __iomem *membase;
+	struct resource *r;
+	struct vm_wdt_s *vm_wdt;
+	u32 wdt_clock, wdt_timeout_sec = 0;
+
+	r = platform_get_resource(dev, IORESOURCE_MEM, 0);
+	if (r == NULL)
+		return -ENOENT;
+
+	vm_wdt = alloc_percpu(typeof(struct vm_wdt_s));
+	if (!vm_wdt)
+		return -ENOMEM;
+
+	membase = ioremap(r->start, resource_size(r));
+	if (!membase) {
+		ret = -ENXIO;
+		goto err_withmem;
+	}
+
+	virt_dev = dev;
+	platform_set_drvdata(dev, vm_wdt);
+	if (of_property_read_u32(dev->dev.of_node, "clock-frequency",
+				 &wdt_clock))
+		wdt_clock = VMWDT_DEFAULT_CLOCK_HZ;
+
+	if (of_property_read_u32(dev->dev.of_node, "timeout-sec",
+				 &wdt_timeout_sec))
+		wdt_timeout_sec = VMWDT_DEFAULT_TIMEOT_SEC;
+
+	for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask) {
+		struct vm_wdt_s *cpu_wdt = per_cpu_ptr(vm_wdt, cpu);
+
+		cpu_wdt->membase = membase + cpu * VMWDT_REG_LEN;
+		cpu_wdt->clock_freq = wdt_clock;
+		cpu_wdt->expiration_sec = wdt_timeout_sec;
+		cpu_wdt->ping_timeout_ms = wdt_timeout_sec * MSEC_PER_SEC / 2;
+		smp_call_function_single(cpu, vmwdt_start, cpu_wdt, true);
+	}
+
+	err = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
+					"virt/watchdog:online",
+					start_watchdog_on_cpu,
+					stop_watchdog_on_cpu);
+	if (err < 0) {
+		dev_warn(&dev->dev, "failed to install cpu hotplug");
+		ret = err;
+		goto err_withmem;
+	}
+
+	return 0;
+
+err_withmem:
+	free_percpu(vm_wdt);
+	return ret;
+}
+
+static int vmwdt_remove(struct platform_device *dev)
+{
+	int cpu;
+	struct vm_wdt_s *vm_wdt = platform_get_drvdata(dev);
+
+	for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask) {
+		struct vm_wdt_s *cpu_wdt = per_cpu_ptr(vm_wdt, cpu);
+
+		smp_call_function_single(cpu, vmwdt_stop, cpu_wdt, true);
+	}
+
+	free_percpu(vm_wdt);
+	return 0;
+}
+
+static const struct of_device_id vmwdt_of_match[] = {
+	{ .compatible = "qemu,vm-watchdog", },
+	{}
+};
+
+MODULE_DEVICE_TABLE(of, vm_watchdog_of_match);
+
+static struct platform_driver vmwdt_driver = {
+	.probe  = vmwdt_probe,
+	.remove = vmwdt_remove,
+	.driver = {
+		.name           = KBUILD_MODNAME,
+		.of_match_table = vmwdt_of_match,
+	},
+};
+
+module_platform_driver(vmwdt_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Sebastian Ene <sebastianene@google.com>");
+MODULE_DESCRIPTION("Virtual watchdog driver");
-- 
2.36.0.464.gb9c8b46e94-goog