[PATCH v8 0/2] Detect stalls on guest vCPUS

[PATCH v8 0/2] Detect stalls on guest vCPUS

[Sebastian Ene]

This adds a mechanism to detect stalls on the guest vCPUS by creating a
per CPU hrtimer which periodically 'pets' the host backend driver.
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 basis.

This device driver acts as a soft lockup detector by relying on the host
backend driver to measure the elapesed time between subsequent 'pet' events.
If the elapsed time doesn't match an expected value, the backend driver
decides that the guest vCPU is locked and resets the guest. The host
backend driver takes into account the time that the guest is not
running. The communication with the backend driver is done through MMIO
and the register layout of the virtual watchdog is described as part of
the backend driver changes.

The host backend driver is implemented as part of:
https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3548817

Changelog v8:
 - fix the yamlint dtschema warning caused by the missing 'reg' property 

Changelog v7:
 - fix the dtschema warnings for 'timeout-sec' property
 - rename vcpu_stall_detector.yaml to qemu,vcpu_stall_detector.yaml and
   place the file under misc
 - improve the Kconfig description for the driver by making it KVM
   specific

Changelog v6:
 - fix issues reported by lkp@intel robot:
     building for ARCH=h8300 incorrect type in assignment
     (different address spaces)

Sebastian Ene (2):
  dt-bindings: vcpu_stall_detector: Add qemu,vcpu-stall-detector
    compatible
  misc: Add a mechanism to detect stalls on guest vCPUs

 .../misc/qemu,vcpu-stall-detector.yaml        |  51 ++++
 drivers/misc/Kconfig                          |  12 +
 drivers/misc/Makefile                         |   1 +
 drivers/misc/vcpu_stall_detector.c            | 222 ++++++++++++++++++
 4 files changed, 286 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/misc/qemu,vcpu-stall-detector.yaml
 create mode 100644 drivers/misc/vcpu_stall_detector.c

-- 
2.37.0.rc0.161.g10f37bed90-goog

[PATCH v8 1/2] dt-bindings: vcpu_stall_detector: Add qemu,vcpu-stall-detector compatible

[Sebastian Ene]

The VCPU stall detection mechanism allows to configure the expiration
duration and the internal counter clock frequency measured in Hz.
Add these properties in the schema.

While this is a memory mapped virtual device, it is expected to be loaded
when the DT contains the compatible: "qemu,vcpu-stall-detector" node.
In a protected VM we trust the generated DT nodes and we don't rely on
the host to present the hardware peripherals.

Signed-off-by: Sebastian Ene <sebastianene@google.com>
---
 .../misc/qemu,vcpu-stall-detector.yaml        | 51 +++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/misc/qemu,vcpu-stall-detector.yaml

diff --git a/Documentation/devicetree/bindings/misc/qemu,vcpu-stall-detector.yaml b/Documentation/devicetree/bindings/misc/qemu,vcpu-stall-detector.yaml
new file mode 100644
index 000000000000..1aebeb696ee0
--- /dev/null
+++ b/Documentation/devicetree/bindings/misc/qemu,vcpu-stall-detector.yaml
@@ -0,0 +1,51 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/misc/qemu,vcpu-stall-detector.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: VCPU stall detector
+
+description:
+  This binding describes a CPU stall detector mechanism for virtual CPUs
+  which is accessed through MMIO.
+
+maintainers:
+  - Sebastian Ene <sebastianene@google.com>
+
+properties:
+  compatible:
+    enum:
+      - qemu,vcpu-stall-detector
+
+  reg:
+    maxItems: 1
+
+  clock-frequency:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description: |
+      The internal clock of the stall detector peripheral measure in Hz used
+      to decrement its internal counter register on each tick.
+      Defaults to 10 if unset.
+    default: 10
+
+  timeout-sec:
+    description: |
+      The stall detector expiration timeout measured in seconds.
+      Defaults to 8 if unset. Please note that it also takes into account the
+      time spent while the VCPU is not running.
+    default: 8
+
+required:
+  - compatible
+
+additionalProperties: false
+
+examples:
+  - |
+    vmwdt@9030000 {
+      compatible = "qemu,vcpu-stall-detector";
+      reg = <0x9030000 0x10000>;
+      clock-frequency = <10>;
+      timeout-sec = <8>;
+    };
-- 
2.37.0.rc0.161.g10f37bed90-goog

[PATCH v8 2/2] misc: Add a mechanism to detect stalls on guest vCPUs

[Sebastian Ene]

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/vcpu_stall_detector.c | 222 +++++++++++++++++++++++++++++
 3 files changed, 235 insertions(+)
 create mode 100644 drivers/misc/vcpu_stall_detector.c

diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index 41d2bb0ae23a..e15c85d74c4b 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -483,6 +483,18 @@ config OPEN_DICE
 
 	  If unsure, say N.
 
+config VCPU_STALL_DETECTOR
+	tristate "VCPU stall detector"
+	select LOCKUP_DETECTOR
+	help
+	  Detect CPU locks on a kvm 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 vcpu_stall_detector.
+
 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..8b33f04a9719
--- /dev/null
+++ b/drivers/misc/vcpu_stall_detector.c
@@ -0,0 +1,222 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// 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 REG_STATUS		(0x00)
+#define REG_LOAD_CNT		(0x04)
+#define REG_CURRENT_CNT		(0x08)
+#define REG_CLOCK_FREQ_HZ	(0x0C)
+#define REG_LEN			(0x10)
+
+#define DEFAULT_CLOCK_HZ	(10)
+#define DEFAULT_TIMEOT_SEC	(8)
+
+struct vm_stall_detect_s {
+	void __iomem *membase;
+	u32 clock_freq;
+	u32 expiration_sec;
+	u32 ping_timeout_ms;
+	struct hrtimer per_cpu_hrtimer;
+	struct platform_device *dev;
+};
+
+#define vcpu_stall_detect_reg_write(stall_detect, reg, value)	\
+	iowrite32((value), (stall_detect)->membase + (reg))
+#define vcpu_stall_detect_reg_read(stall_detect, reg)		\
+	io32read((stall_detect)->membase + (reg))
+
+static struct platform_device *virt_dev;
+
+static enum hrtimer_restart
+vcpu_stall_detect_timer_fn(struct hrtimer *hrtimer)
+{
+	struct vm_stall_detect_s *cpu_stall_detect;
+	u32 ticks;
+
+	cpu_stall_detect = container_of(hrtimer, struct vm_stall_detect_s,
+					per_cpu_hrtimer);
+	ticks = cpu_stall_detect->clock_freq *
+		cpu_stall_detect->expiration_sec;
+	vcpu_stall_detect_reg_write(cpu_stall_detect, REG_LOAD_CNT, ticks);
+	hrtimer_forward_now(hrtimer,
+			    ms_to_ktime(cpu_stall_detect->ping_timeout_ms));
+
+	return HRTIMER_RESTART;
+}
+
+static void vcpu_stall_detect_start(void *arg)
+{
+	u32 ticks;
+	struct vm_stall_detect_s *cpu_stall_detect = arg;
+	struct hrtimer *hrtimer = &cpu_stall_detect->per_cpu_hrtimer;
+
+	vcpu_stall_detect_reg_write(cpu_stall_detect, REG_CLOCK_FREQ_HZ,
+			cpu_stall_detect->clock_freq);
+
+	/* 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 = cpu_stall_detect->clock_freq *
+		cpu_stall_detect->expiration_sec;
+	vcpu_stall_detect_reg_write(cpu_stall_detect, REG_LOAD_CNT, ticks);
+
+	/* Enable the internal clock and start the stall detector */
+	vcpu_stall_detect_reg_write(cpu_stall_detect, REG_STATUS, 1);
+
+	hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	hrtimer->function = vcpu_stall_detect_timer_fn;
+	hrtimer_start(hrtimer, ms_to_ktime(cpu_stall_detect->ping_timeout_ms),
+		      HRTIMER_MODE_REL_PINNED);
+}
+
+static void vcpu_stall_detect_stop(void *arg)
+{
+	struct vm_stall_detect_s *cpu_stall_detect = arg;
+	struct hrtimer *hrtimer = &cpu_stall_detect->per_cpu_hrtimer;
+
+	hrtimer_cancel(hrtimer);
+
+	/* Disable the stall detector */
+	vcpu_stall_detect_reg_write(cpu_stall_detect, REG_STATUS, 0);
+}
+
+static int start_stall_detector_on_cpu(unsigned int cpu)
+{
+	struct vm_stall_detect_s __percpu *vm_stall_detect;
+
+	vm_stall_detect = (struct vm_stall_detect_s __percpu *)
+		platform_get_drvdata(virt_dev);
+	vcpu_stall_detect_start(this_cpu_ptr(vm_stall_detect));
+	return 0;
+}
+
+static int stop_stall_detector_on_cpu(unsigned int cpu)
+{
+	struct vm_stall_detect_s __percpu *vm_stall_detect;
+
+	vm_stall_detect = (struct vm_stall_detect_s __percpu *)
+		platform_get_drvdata(virt_dev);
+	vcpu_stall_detect_stop(this_cpu_ptr(vm_stall_detect));
+	return 0;
+}
+
+static int vcpu_stall_detect_probe(struct platform_device *dev)
+{
+	int cpu, ret, err;
+	void __iomem *membase;
+	struct resource *r;
+	struct vm_stall_detect_s __percpu *vm_stall_detect;
+	u32 stall_detect_clock, stall_detect_timeout_sec = 0;
+
+	r = platform_get_resource(dev, IORESOURCE_MEM, 0);
+	if (r == NULL)
+		return -ENOENT;
+
+	vm_stall_detect = alloc_percpu(typeof(struct vm_stall_detect_s));
+	if (!vm_stall_detect)
+		return -ENOMEM;
+
+	membase = ioremap(r->start, resource_size(r));
+	if (!membase) {
+		ret = -ENXIO;
+		goto err_withmem;
+	}
+
+	virt_dev = dev;
+	platform_set_drvdata(dev, vm_stall_detect);
+	if (of_property_read_u32(dev->dev.of_node, "clock-frequency",
+				 &stall_detect_clock))
+		stall_detect_clock = DEFAULT_CLOCK_HZ;
+
+	if (of_property_read_u32(dev->dev.of_node, "timeout-sec",
+				 &stall_detect_timeout_sec))
+		stall_detect_timeout_sec = DEFAULT_TIMEOT_SEC;
+
+	for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask) {
+		struct vm_stall_detect_s *cpu_stall_detect;
+
+		cpu_stall_detect = per_cpu_ptr(vm_stall_detect, cpu);
+		cpu_stall_detect->membase = membase + cpu * REG_LEN;
+		cpu_stall_detect->clock_freq = stall_detect_clock;
+		cpu_stall_detect->expiration_sec = stall_detect_timeout_sec;
+		cpu_stall_detect->ping_timeout_ms = stall_detect_timeout_sec *
+			MSEC_PER_SEC / 2;
+		smp_call_function_single(cpu, vcpu_stall_detect_start,
+					 cpu_stall_detect, true);
+	}
+
+	err = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
+					"virt/vcpu_stall_detector:online",
+					start_stall_detector_on_cpu,
+					stop_stall_detector_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_stall_detect);
+	return ret;
+}
+
+static int vcpu_stall_detect_remove(struct platform_device *dev)
+{
+	int cpu;
+	struct vm_stall_detect_s __percpu *vm_stall_detect;
+
+	vm_stall_detect = (struct vm_stall_detect_s __percpu *)
+		platform_get_drvdata(dev);
+	for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask) {
+		struct vm_stall_detect_s *cpu_stall_detect;
+
+		cpu_stall_detect = per_cpu_ptr(vm_stall_detect, cpu);
+		smp_call_function_single(cpu, vcpu_stall_detect_stop,
+					 cpu_stall_detect, true);
+	}
+
+	free_percpu(vm_stall_detect);
+	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@google.com>");
+MODULE_DESCRIPTION("VCPU stall detector");
-- 
2.37.0.rc0.161.g10f37bed90-goog

Re: [PATCH v8 2/2] misc: Add a mechanism to detect stalls on guest vCPUs

[Guenter Roeck]

On 6/27/22 03:28, 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
> 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>

Couple of nitpicks.

> ---
>   drivers/misc/Kconfig               |  12 ++
>   drivers/misc/Makefile              |   1 +
>   drivers/misc/vcpu_stall_detector.c | 222 +++++++++++++++++++++++++++++
>   3 files changed, 235 insertions(+)
>   create mode 100644 drivers/misc/vcpu_stall_detector.c
> 
> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> index 41d2bb0ae23a..e15c85d74c4b 100644
> --- a/drivers/misc/Kconfig
> +++ b/drivers/misc/Kconfig
> @@ -483,6 +483,18 @@ config OPEN_DICE
>   
>   	  If unsure, say N.
>   
> +config VCPU_STALL_DETECTOR
> +	tristate "VCPU stall detector"
> +	select LOCKUP_DETECTOR

depends on OF ?

> +	help
> +	  Detect CPU locks on a kvm 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 vcpu_stall_detector.
> +
>   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..8b33f04a9719
> --- /dev/null
> +++ b/drivers/misc/vcpu_stall_detector.c
> @@ -0,0 +1,222 @@
> +// SPDX-License-Identifier: GPL-2.0
> +//
> +// 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 REG_STATUS		(0x00)
> +#define REG_LOAD_CNT		(0x04)
> +#define REG_CURRENT_CNT		(0x08)
> +#define REG_CLOCK_FREQ_HZ	(0x0C)
> +#define REG_LEN			(0x10)
> +
> +#define DEFAULT_CLOCK_HZ	(10)
> +#define DEFAULT_TIMEOT_SEC	(8)
> +
> +struct vm_stall_detect_s {
> +	void __iomem *membase;
> +	u32 clock_freq;
> +	u32 expiration_sec;
> +	u32 ping_timeout_ms;
> +	struct hrtimer per_cpu_hrtimer;
> +	struct platform_device *dev;
> +};
> +
> +#define vcpu_stall_detect_reg_write(stall_detect, reg, value)	\
> +	iowrite32((value), (stall_detect)->membase + (reg))
> +#define vcpu_stall_detect_reg_read(stall_detect, reg)		\
> +	io32read((stall_detect)->membase + (reg))
> +
> +static struct platform_device *virt_dev;
> +

virt_dev is only used to call platform_set_drvdata() and platform_get_drvdata()
on it. Why not just have a static variable named vm_stall_detect ?

> +static enum hrtimer_restart
> +vcpu_stall_detect_timer_fn(struct hrtimer *hrtimer)
> +{
> +	struct vm_stall_detect_s *cpu_stall_detect;
> +	u32 ticks;
> +
> +	cpu_stall_detect = container_of(hrtimer, struct vm_stall_detect_s,
> +					per_cpu_hrtimer);
> +	ticks = cpu_stall_detect->clock_freq *
> +		cpu_stall_detect->expiration_sec;

Does this really require a continuation line ?

> +	vcpu_stall_detect_reg_write(cpu_stall_detect, REG_LOAD_CNT, ticks);
> +	hrtimer_forward_now(hrtimer,
> +			    ms_to_ktime(cpu_stall_detect->ping_timeout_ms));
> +
> +	return HRTIMER_RESTART;
> +}
> +
> +static void vcpu_stall_detect_start(void *arg)
> +{
> +	u32 ticks;
> +	struct vm_stall_detect_s *cpu_stall_detect = arg;
> +	struct hrtimer *hrtimer = &cpu_stall_detect->per_cpu_hrtimer;
> +
> +	vcpu_stall_detect_reg_write(cpu_stall_detect, REG_CLOCK_FREQ_HZ,
> +			cpu_stall_detect->clock_freq);

CHECK: Alignment should match open parenthesis

> +
> +	/* 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 = cpu_stall_detect->clock_freq *
> +		cpu_stall_detect->expiration_sec;
> +	vcpu_stall_detect_reg_write(cpu_stall_detect, REG_LOAD_CNT, ticks);
> +
> +	/* Enable the internal clock and start the stall detector */
> +	vcpu_stall_detect_reg_write(cpu_stall_detect, REG_STATUS, 1);
> +
> +	hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> +	hrtimer->function = vcpu_stall_detect_timer_fn;
> +	hrtimer_start(hrtimer, ms_to_ktime(cpu_stall_detect->ping_timeout_ms),
> +		      HRTIMER_MODE_REL_PINNED);
> +}
> +
> +static void vcpu_stall_detect_stop(void *arg)
> +{
> +	struct vm_stall_detect_s *cpu_stall_detect = arg;
> +	struct hrtimer *hrtimer = &cpu_stall_detect->per_cpu_hrtimer;
> +
> +	hrtimer_cancel(hrtimer);
> +
> +	/* Disable the stall detector */
> +	vcpu_stall_detect_reg_write(cpu_stall_detect, REG_STATUS, 0);
> +}
> +
> +static int start_stall_detector_on_cpu(unsigned int cpu)
> +{
> +	struct vm_stall_detect_s __percpu *vm_stall_detect;
> +
> +	vm_stall_detect = (struct vm_stall_detect_s __percpu *)
> +		platform_get_drvdata(virt_dev);

platform_get_drvdata() returns void *; typecast to it is unnecessary.


> +	vcpu_stall_detect_start(this_cpu_ptr(vm_stall_detect));
> +	return 0;
> +}
> +
> +static int stop_stall_detector_on_cpu(unsigned int cpu)
> +{
> +	struct vm_stall_detect_s __percpu *vm_stall_detect;
> +
> +	vm_stall_detect = (struct vm_stall_detect_s __percpu *)
> +		platform_get_drvdata(virt_dev);

Same as above.

> +	vcpu_stall_detect_stop(this_cpu_ptr(vm_stall_detect));
> +	return 0;
> +}
> +
> +static int vcpu_stall_detect_probe(struct platform_device *dev)
> +{
> +	int cpu, ret, err;
> +	void __iomem *membase;
> +	struct resource *r;
> +	struct vm_stall_detect_s __percpu *vm_stall_detect;
> +	u32 stall_detect_clock, stall_detect_timeout_sec = 0;
> +
> +	r = platform_get_resource(dev, IORESOURCE_MEM, 0);
> +	if (r == NULL)

	if (!r)

> +		return -ENOENT;

"No such file or directory" seems odd. Usually I see ENODEV, ENXIO,
or EINVAL here.

> +
> +	vm_stall_detect = alloc_percpu(typeof(struct vm_stall_detect_s));
> +	if (!vm_stall_detect)
> +		return -ENOMEM;
> +
> +	membase = ioremap(r->start, resource_size(r));
> +	if (!membase) {
> +		ret = -ENXIO;

The typical return value here is -ENOMEM.

> +		goto err_withmem;
> +	}
> +
> +	virt_dev = dev;
> +	platform_set_drvdata(dev, vm_stall_detect);
> +	if (of_property_read_u32(dev->dev.of_node, "clock-frequency",
> +				 &stall_detect_clock))
> +		stall_detect_clock = DEFAULT_CLOCK_HZ;
> +
> +	if (of_property_read_u32(dev->dev.of_node, "timeout-sec",
> +				 &stall_detect_timeout_sec))
> +		stall_detect_timeout_sec = DEFAULT_TIMEOT_SEC;
> +
> +	for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask) {
> +		struct vm_stall_detect_s *cpu_stall_detect;
> +
> +		cpu_stall_detect = per_cpu_ptr(vm_stall_detect, cpu);
> +		cpu_stall_detect->membase = membase + cpu * REG_LEN;
> +		cpu_stall_detect->clock_freq = stall_detect_clock;
> +		cpu_stall_detect->expiration_sec = stall_detect_timeout_sec;
> +		cpu_stall_detect->ping_timeout_ms = stall_detect_timeout_sec *
> +			MSEC_PER_SEC / 2;

Please add a comment to explain division by 2.

> +		smp_call_function_single(cpu, vcpu_stall_detect_start,
> +					 cpu_stall_detect, true);
> +	}
> +
> +	err = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
> +					"virt/vcpu_stall_detector:online",
> +					start_stall_detector_on_cpu,
> +					stop_stall_detector_on_cpu);
> +	if (err < 0) {
> +		dev_warn(&dev->dev, "failed to install cpu hotplug");

Why dev_warn() and not dev_err() ?

> +		ret = err;
> +		goto err_withmem;
> +	}
> +
> +	return 0;
> +
> +err_withmem:
> +	free_percpu(vm_stall_detect);
> +	return ret;
> +}
> +
> +static int vcpu_stall_detect_remove(struct platform_device *dev)
> +{
> +	int cpu;
> +	struct vm_stall_detect_s __percpu *vm_stall_detect;
> +
> +	vm_stall_detect = (struct vm_stall_detect_s __percpu *)
> +		platform_get_drvdata(dev);

Same as above - unnecessary typecast.

> +	for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask) {
> +		struct vm_stall_detect_s *cpu_stall_detect;
> +
> +		cpu_stall_detect = per_cpu_ptr(vm_stall_detect, cpu);
> +		smp_call_function_single(cpu, vcpu_stall_detect_stop,
> +					 cpu_stall_detect, true);
> +	}
> +
> +	free_percpu(vm_stall_detect);
> +	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,

Either use of_match_ptr() or add dependency on OF.

> +	},
> +};
> +
> +module_platform_driver(vcpu_stall_detect_driver);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Sebastian Ene <sebastianene@google.com>");
> +MODULE_DESCRIPTION("VCPU stall detector");

Re: [PATCH v8 2/2] misc: Add a mechanism to detect stalls on guest vCPUs

[Sebastian Ene]

On Tue, Jun 28, 2022 at 07:00:05AM -0700, Guenter Roeck wrote:
> On 6/28/22 02:54, Sebastian Ene wrote:
> [ ... ]
> > > > +static struct platform_device *virt_dev;
> > > > +

Hi,

> > > 
> > > virt_dev is only used to call platform_set_drvdata() and platform_get_drvdata()
> > > on it. Why not just have a static variable named vm_stall_detect ?
> > > 
> > 
> > I think this should also work. I wanted to make use of the provided APIs
> > like platform_set/platform_get.
> > 
> 
> That doesn't mean such APIs should be used just to get used, though.
> 

I will remove these calls and keep it static.

> > > > +
> > > > +	vm_stall_detect = (struct vm_stall_detect_s __percpu *)
> > > > +		platform_get_drvdata(virt_dev);
> > > 
> > > platform_get_drvdata() returns void *; typecast to it is unnecessary.
> > > 
> > > 
> > 
> > I needed this typecast because the variable is per-cpu and some
> > compilers(eg. gcc for ARCH=h8300) complain if we don't specify this
> > hint.
> > 
> Hmm, interesting. I didn't know that. We live and learn.
> Though h8300 is gone now :-)

I had some Intel robot complaining about this in my previous series(v5) and
I fixed the warnings by adding these compiler hints.

> 
> Did you reply in private on purpose ?
> 

I misused my CC list but I will fix this in my reply. 

> Thanks,
> Guenter

Thanks for the response,
Seb

Re: [PATCH v8 1/2] dt-bindings: vcpu_stall_detector: Add qemu,vcpu-stall-detector compatible

[Rob Herring]

On Mon, 27 Jun 2022 10:28:11 +0000, Sebastian Ene wrote:
> The VCPU stall detection mechanism allows to configure the expiration
> duration and the internal counter clock frequency measured in Hz.
> Add these properties in the schema.
> 
> While this is a memory mapped virtual device, it is expected to be loaded
> when the DT contains the compatible: "qemu,vcpu-stall-detector" node.
> In a protected VM we trust the generated DT nodes and we don't rely on
> the host to present the hardware peripherals.
> 
> Signed-off-by: Sebastian Ene <sebastianene@google.com>
> ---
>  .../misc/qemu,vcpu-stall-detector.yaml        | 51 +++++++++++++++++++
>  1 file changed, 51 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/misc/qemu,vcpu-stall-detector.yaml
> 

Reviewed-by: Rob Herring <robh@kernel.org>