A new virtio pci driver is added for listening to vcpus
inside guest. Each vcpu creates a corresponding thread to
periodically send data to qemu's back-end watchdog device.
If a vCPU is in the stall state, data cannot be sent to
back-end virtio device. As a result, the back-end device
can detect that the guest is in the stall state.

The driver is mainly used with the back-end watchdog device of qemu.

The qemu backend watchdog device is implemented as follow:
https://lore.kernel.org/qemu-devel/20230705081813.411526-1-zhanghao1@kylinos.cn/

Signed-off-by: zhanghao1 <zhanghao1@kylinos.cn>
---
 drivers/virtio/Kconfig                      |   9 +
 drivers/virtio/Makefile                     |   1 +
 drivers/virtio/virtio_vcpu_stall_detector.c | 299 ++++++++++++++++++++
 3 files changed, 309 insertions(+)
 create mode 100644 drivers/virtio/virtio_vcpu_stall_detector.c

diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index 0a53a61231c2..869323e345a1 100644
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -173,4 +173,13 @@ config VIRTIO_DMA_SHARED_BUFFER
 	 This option adds a flavor of dma buffers that are backed by
 	 virtio resources.
 
+config VIRTIO_VCPU_WATCHDOG
+	tristate "Virtio vcpu watchdog driver"
+	depends on VIRTIO_PCI
+	help
+	 When this driver is bound inside a KVM guest, it will
+	 periodically "pet" an PCI virtio watchdog device from each vCPU
+	 and allow the host to detect vCPU stalls.
+
+	 If you do not intend to run this kernel as a guest, say N.
 endif # VIRTIO_MENU
diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
index 8e98d24917cc..c7341f078a34 100644
--- a/drivers/virtio/Makefile
+++ b/drivers/virtio/Makefile
@@ -12,3 +12,4 @@ obj-$(CONFIG_VIRTIO_INPUT) += virtio_input.o
 obj-$(CONFIG_VIRTIO_VDPA) += virtio_vdpa.o
 obj-$(CONFIG_VIRTIO_MEM) += virtio_mem.o
 obj-$(CONFIG_VIRTIO_DMA_SHARED_BUFFER) += virtio_dma_buf.o
+obj-$(CONFIG_VIRTIO_VCPU_WATCHDOG) += virtio_vcpu_stall_detector.o
diff --git a/drivers/virtio/virtio_vcpu_stall_detector.c b/drivers/virtio/virtio_vcpu_stall_detector.c
new file mode 100644
index 000000000000..58344ca528be
--- /dev/null
+++ b/drivers/virtio/virtio_vcpu_stall_detector.c
@@ -0,0 +1,299 @@
+// SPDX-License-Identifier: GPL-2.0-only
+//
+// VCPU stall detector.
+// Copyright (C) Kylin Software, 2023
+
+#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 <uapi/linux/virtio_ids.h>
+#include <linux/virtio_config.h>
+#include <linux/param.h>
+#include <linux/percpu.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_REG_TIMEOUT_SEC	(0x14)
+
+#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;
+
+	enum cpuhp_state hp_online;
+};
+
+struct vcpu_stall_priv {
+	struct hrtimer vcpu_hrtimer;
+	struct virtio_device *vdev;
+	u32 cpu_id;
+};
+
+struct vcpu_stall {
+	struct vcpu_stall_priv *priv;
+	struct virtqueue *vq;
+	spinlock_t lock;
+	struct pet_event {
+		u32 cpu_id;
+		bool is_initialized;
+		u32 ticks;
+	} pet_event;
+};
+
+static const struct virtio_device_id vcpu_stall_id_table[] = {
+	{ VIRTIO_ID_WATCHDOG, VIRTIO_DEV_ANY_ID },
+	{ 0, },
+};
+
+/* The vcpu stall configuration structure which applies to all the CPUs */
+static struct vcpu_stall_detect_config vcpu_stall_config;
+static struct vcpu_stall *vcpu_stall;
+
+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;
+	struct scatterlist sg;
+	int unused, err = 0;
+
+	struct vcpu_stall_priv *vcpu_stall_detector =
+		this_cpu_ptr(vcpu_stall->priv);
+
+	/* 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;
+
+	spin_lock(&vcpu_stall->lock);
+	while (virtqueue_get_buf(vcpu_stall->vq, &unused))
+		;
+	vcpu_stall->pet_event.ticks = cpu_to_virtio32(vcpu_stall_detector->vdev, ticks);
+	vcpu_stall->pet_event.is_initialized = true;
+	vcpu_stall->pet_event.cpu_id = vcpu_stall_detector->cpu_id;
+
+	sg_init_one(&sg, &vcpu_stall->pet_event, sizeof(vcpu_stall->pet_event));
+	err = virtqueue_add_outbuf(vcpu_stall->vq, &sg, 1, vcpu_stall, GFP_ATOMIC);
+	if (!err)
+		virtqueue_kick(vcpu_stall->vq);
+	else
+		pr_err("cpu:%d failed to add outbuf, err:%d\n", vcpu_stall_detector->cpu_id, err);
+
+	spin_unlock(&vcpu_stall->lock);
+
+	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 scatterlist sg;
+	struct hrtimer *vcpu_hrtimer;
+	int err = 0;
+
+	struct vcpu_stall_priv *vcpu_stall_detector =
+		this_cpu_ptr(vcpu_stall->priv);
+
+	vcpu_stall_detector->cpu_id = cpu;
+
+	vcpu_hrtimer = &vcpu_stall_detector->vcpu_hrtimer;
+
+	/* 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->pet_event.ticks = cpu_to_virtio32(vcpu_stall_detector->vdev, ticks);
+
+	/* 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->pet_event.is_initialized = true;
+
+	spin_lock(&vcpu_stall->lock);
+	vcpu_stall->pet_event.cpu_id = cpu;
+	sg_init_one(&sg, &vcpu_stall->pet_event, sizeof(vcpu_stall->pet_event));
+	err = virtqueue_add_outbuf(vcpu_stall->vq, &sg, 1, vcpu_stall, GFP_ATOMIC);
+	if (!err)
+		virtqueue_kick(vcpu_stall->vq);
+
+	spin_unlock(&vcpu_stall->lock);
+
+	hrtimer_start(vcpu_hrtimer, ms_to_ktime(ping_timeout_ms),
+		      HRTIMER_MODE_REL_PINNED);
+	return err;
+}
+
+static int stop_stall_detector_cpu(unsigned int cpu)
+{
+	int err = 0;
+	struct scatterlist sg;
+
+	struct vcpu_stall_priv *vcpu_stall_detector =
+		per_cpu_ptr(vcpu_stall_detectors, cpu);
+
+	/* Disable the stall detector for the current CPU */
+	hrtimer_cancel(&vcpu_stall_detector->vcpu_hrtimer);
+	vcpu_stall->pet_event.is_initialized = false;
+	vcpu_stall->pet_event.cpu_id = cpu;
+
+	spin_lock(&vcpu_stall->lock);
+	sg_init_one(&sg, &vcpu_stall->pet_event, sizeof(vcpu_stall->pet_event));
+	err = virtqueue_add_outbuf(vcpu_stall->vq, &sg, 1, vcpu_stall, GFP_ATOMIC);
+	if (!err)
+		virtqueue_kick(vcpu_stall->vq);
+
+	spin_unlock(&vcpu_stall->lock);
+
+	return err;
+}
+
+static int vcpu_stall_detect_probe(struct virtio_device *vdev)
+{
+	int ret, cpu;
+	u32 clock_freq_hz = VCPU_STALL_DEFAULT_CLOCK_HZ;
+	u32 stall_timeout_sec = VCPU_STALL_DEFAULT_TIMEOUT_SEC;
+
+	vcpu_stall = kzalloc(sizeof(struct vcpu_stall), GFP_KERNEL);
+	if (!vcpu_stall) {
+		ret = -ENOMEM;
+		goto err;
+	}
+	vdev->priv = vcpu_stall;
+
+	vcpu_stall->priv = devm_alloc_percpu(&vdev->dev,
+					typeof(struct vcpu_stall_priv));
+	if (!vcpu_stall->priv) {
+		ret = -ENOMEM;
+		goto failed_priv;
+	}
+
+	for_each_possible_cpu(cpu) {
+		struct vcpu_stall_priv *priv;
+
+		priv = per_cpu_ptr(vcpu_stall->priv, cpu);
+		priv->vdev = vdev;
+	}
+
+	ret = virtio_cread_feature(vdev, VCPU_STALL_REG_CLOCK_FREQ_HZ,
+						struct vcpu_stall_detect_config, clock_freq_hz,
+						&clock_freq_hz);
+	if (ret || !clock_freq_hz) {
+		if (!(clock_freq_hz > 0 &&
+		      clock_freq_hz < VCPU_STALL_MAX_CLOCK_HZ)) {
+			dev_warn(&vdev->dev, "clk out of range\n");
+			clock_freq_hz = VCPU_STALL_DEFAULT_CLOCK_HZ;
+		}
+	}
+	ret = virtio_cread_feature(vdev, VCPU_STALL_REG_TIMEOUT_SEC,
+						struct vcpu_stall_detect_config, stall_timeout_sec,
+						&stall_timeout_sec);
+	if (ret || !stall_timeout_sec) {
+		if (!(stall_timeout_sec > 0 &&
+		      stall_timeout_sec < VCPU_STALL_MAX_TIMEOUT_SEC)) {
+			dev_warn(&vdev->dev, "stall timeout out of range\n");
+			stall_timeout_sec = VCPU_STALL_DEFAULT_TIMEOUT_SEC;
+		}
+	}
+
+	vcpu_stall_config = (struct vcpu_stall_detect_config) {
+		.clock_freq_hz		= clock_freq_hz,
+		.stall_timeout_sec	= stall_timeout_sec
+	};
+
+	/* find virtqueue for guest to send pet event to host */
+	vcpu_stall->vq = virtio_find_single_vq(vdev, NULL, "pet-event");
+	if (IS_ERR(vcpu_stall->vq)) {
+		dev_err(&vdev->dev, "failed to find vq\n");
+		goto failed_priv;
+	}
+
+	spin_lock_init(&vcpu_stall->lock);
+
+	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(&vdev->dev, "failed to install cpu hotplug\n");
+		goto failed_priv;
+	}
+
+	vcpu_stall_config.hp_online = ret;
+	return 0;
+
+
+failed_priv:
+	kfree(vcpu_stall);
+err:
+	return ret;
+}
+
+static void vcpu_stall_detect_remove(struct virtio_device *vdev)
+{
+	int cpu;
+
+	cpuhp_remove_state(vcpu_stall_config.hp_online);
+
+	for_each_possible_cpu(cpu)
+		stop_stall_detector_cpu(cpu);
+}
+
+static unsigned int features_legacy[] = {
+	VCPU_STALL_REG_STATUS, VCPU_STALL_REG_LOAD_CNT, VCPU_STALL_REG_CURRENT_CNT,
+	VCPU_STALL_REG_CLOCK_FREQ_HZ, VCPU_STALL_REG_LEN, VCPU_STALL_REG_TIMEOUT_SEC
+};
+
+
+static unsigned int features[] = {
+	VCPU_STALL_REG_STATUS, VCPU_STALL_REG_LOAD_CNT, VCPU_STALL_REG_CURRENT_CNT,
+	VCPU_STALL_REG_CLOCK_FREQ_HZ, VCPU_STALL_REG_LEN, VCPU_STALL_REG_TIMEOUT_SEC
+};
+
+static struct virtio_driver vcpu_stall_detect_driver = {
+	.feature_table	= features,
+	.feature_table_size = ARRAY_SIZE(features),
+	.feature_table_legacy	= features_legacy,
+	.feature_table_size_legacy	= ARRAY_SIZE(features_legacy),
+	.driver.name	= KBUILD_MODNAME,
+	.driver.owner	= THIS_MODULE,
+	.id_table =	vcpu_stall_id_table,
+	.probe  = vcpu_stall_detect_probe,
+	.remove = vcpu_stall_detect_remove,
+};
+
+module_virtio_driver(vcpu_stall_detect_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_DEVICE_TABLE(virtio, vcpu_stall_id_table);
+MODULE_AUTHOR("zhanghao1 <zhanghao1@kylinos.cn>");
+MODULE_DESCRIPTION("VCPU stall detector");
-- 
2.25.1


No virus found
		Checked by Hillstone Network AntiVirus

On Mon, Jul 31, 2023 at 09:25:12AM +0800, zhanghao1 wrote:
> A new virtio pci driver is added for listening to vcpus
> inside guest. Each vcpu creates a corresponding thread to
> periodically send data to qemu's back-end watchdog device.
> If a vCPU is in the stall state, data cannot be sent to
> back-end virtio device. As a result, the back-end device
> can detect that the guest is in the stall state.
> 
> The driver is mainly used with the back-end watchdog device of qemu.
> 
> The qemu backend watchdog device is implemented as follow:
> https://lore.kernel.org/qemu-devel/20230705081813.411526-1-zhanghao1@kylinos.cn/
> 
> Signed-off-by: zhanghao1 <zhanghao1@kylinos.cn>
> ---
>  drivers/virtio/Kconfig                      |   9 +
>  drivers/virtio/Makefile                     |   1 +
>  drivers/virtio/virtio_vcpu_stall_detector.c | 299 ++++++++++++++++++++
>  3 files changed, 309 insertions(+)
>  create mode 100644 drivers/virtio/virtio_vcpu_stall_detector.c
> 
> diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> index 0a53a61231c2..869323e345a1 100644
> --- a/drivers/virtio/Kconfig
> +++ b/drivers/virtio/Kconfig
> @@ -173,4 +173,13 @@ config VIRTIO_DMA_SHARED_BUFFER
>  	 This option adds a flavor of dma buffers that are backed by
>  	 virtio resources.
>  
> +config VIRTIO_VCPU_WATCHDOG
> +	tristate "Virtio vcpu watchdog driver"
> +	depends on VIRTIO_PCI
> +	help
> +	 When this driver is bound inside a KVM guest, it will
> +	 periodically "pet" an PCI virtio watchdog device from each vCPU
> +	 and allow the host to detect vCPU stalls.
> +
> +	 If you do not intend to run this kernel as a guest, say N.
>  endif # VIRTIO_MENU
> diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
> index 8e98d24917cc..c7341f078a34 100644
> --- a/drivers/virtio/Makefile
> +++ b/drivers/virtio/Makefile
> @@ -12,3 +12,4 @@ obj-$(CONFIG_VIRTIO_INPUT) += virtio_input.o
>  obj-$(CONFIG_VIRTIO_VDPA) += virtio_vdpa.o
>  obj-$(CONFIG_VIRTIO_MEM) += virtio_mem.o
>  obj-$(CONFIG_VIRTIO_DMA_SHARED_BUFFER) += virtio_dma_buf.o
> +obj-$(CONFIG_VIRTIO_VCPU_WATCHDOG) += virtio_vcpu_stall_detector.o
> diff --git a/drivers/virtio/virtio_vcpu_stall_detector.c b/drivers/virtio/virtio_vcpu_stall_detector.c
> new file mode 100644
> index 000000000000..58344ca528be
> --- /dev/null
> +++ b/drivers/virtio/virtio_vcpu_stall_detector.c
> @@ -0,0 +1,299 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +//
> +// VCPU stall detector.
> +// Copyright (C) Kylin Software, 2023
> +
> +#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 <uapi/linux/virtio_ids.h>
> +#include <linux/virtio_config.h>
> +#include <linux/param.h>
> +#include <linux/percpu.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_REG_TIMEOUT_SEC	(0x14)
> +
> +#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;
> +
> +	enum cpuhp_state hp_online;
> +};
> +
> +struct vcpu_stall_priv {
> +	struct hrtimer vcpu_hrtimer;
> +	struct virtio_device *vdev;
> +	u32 cpu_id;
> +};
> +
> +struct vcpu_stall {
> +	struct vcpu_stall_priv *priv;
> +	struct virtqueue *vq;
> +	spinlock_t lock;
> +	struct pet_event {
> +		u32 cpu_id;
> +		bool is_initialized;
> +		u32 ticks;
> +	} pet_event;


should all be LE. and formatting here is very compiler dependent.
also put this in a header under uapi/

> +};
> +
> +static const struct virtio_device_id vcpu_stall_id_table[] = {
> +	{ VIRTIO_ID_WATCHDOG, VIRTIO_DEV_ANY_ID },
> +	{ 0, },
> +};
> +
> +/* The vcpu stall configuration structure which applies to all the CPUs */
> +static struct vcpu_stall_detect_config vcpu_stall_config;
> +static struct vcpu_stall *vcpu_stall;
> +
> +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;
> +	struct scatterlist sg;
> +	int unused, err = 0;
> +
> +	struct vcpu_stall_priv *vcpu_stall_detector =
> +		this_cpu_ptr(vcpu_stall->priv);
> +
> +	/* 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;
> +
> +	spin_lock(&vcpu_stall->lock);
> +	while (virtqueue_get_buf(vcpu_stall->vq, &unused))
> +		;
> +	vcpu_stall->pet_event.ticks = cpu_to_virtio32(vcpu_stall_detector->vdev, ticks);
> +	vcpu_stall->pet_event.is_initialized = true;
> +	vcpu_stall->pet_event.cpu_id = vcpu_stall_detector->cpu_id;
> +
> +	sg_init_one(&sg, &vcpu_stall->pet_event, sizeof(vcpu_stall->pet_event));
> +	err = virtqueue_add_outbuf(vcpu_stall->vq, &sg, 1, vcpu_stall, GFP_ATOMIC);
> +	if (!err)
> +		virtqueue_kick(vcpu_stall->vq);
> +	else
> +		pr_err("cpu:%d failed to add outbuf, err:%d\n", vcpu_stall_detector->cpu_id, err);

this can happen if device is slow to use the buffers. and then what?
will missing the pet even mean host will reset the guest?
pr_err also might make guest crash, depending on config.

> +
> +	spin_unlock(&vcpu_stall->lock);
> +
> +	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 scatterlist sg;
> +	struct hrtimer *vcpu_hrtimer;
> +	int err = 0;
> +
> +	struct vcpu_stall_priv *vcpu_stall_detector =
> +		this_cpu_ptr(vcpu_stall->priv);
> +
> +	vcpu_stall_detector->cpu_id = cpu;
> +
> +	vcpu_hrtimer = &vcpu_stall_detector->vcpu_hrtimer;
> +
> +	/* 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->pet_event.ticks = cpu_to_virtio32(vcpu_stall_detector->vdev, ticks);
> +
> +	/* 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->pet_event.is_initialized = true;
> +
> +	spin_lock(&vcpu_stall->lock);
> +	vcpu_stall->pet_event.cpu_id = cpu;
> +	sg_init_one(&sg, &vcpu_stall->pet_event, sizeof(vcpu_stall->pet_event));
> +	err = virtqueue_add_outbuf(vcpu_stall->vq, &sg, 1, vcpu_stall, GFP_ATOMIC);
> +	if (!err)
> +		virtqueue_kick(vcpu_stall->vq);
> +
> +	spin_unlock(&vcpu_stall->lock);
> +
> +	hrtimer_start(vcpu_hrtimer, ms_to_ktime(ping_timeout_ms),
> +		      HRTIMER_MODE_REL_PINNED);
> +	return err;
> +}
> +
> +static int stop_stall_detector_cpu(unsigned int cpu)
> +{
> +	int err = 0;
> +	struct scatterlist sg;
> +
> +	struct vcpu_stall_priv *vcpu_stall_detector =
> +		per_cpu_ptr(vcpu_stall_detectors, cpu);
> +
> +	/* Disable the stall detector for the current CPU */
> +	hrtimer_cancel(&vcpu_stall_detector->vcpu_hrtimer);
> +	vcpu_stall->pet_event.is_initialized = false;
> +	vcpu_stall->pet_event.cpu_id = cpu;
> +
> +	spin_lock(&vcpu_stall->lock);
> +	sg_init_one(&sg, &vcpu_stall->pet_event, sizeof(vcpu_stall->pet_event));
> +	err = virtqueue_add_outbuf(vcpu_stall->vq, &sg, 1, vcpu_stall, GFP_ATOMIC);
> +	if (!err)
> +		virtqueue_kick(vcpu_stall->vq);
> +
> +	spin_unlock(&vcpu_stall->lock);
> +
> +	return err;
> +}
> +
> +static int vcpu_stall_detect_probe(struct virtio_device *vdev)
> +{
> +	int ret, cpu;
> +	u32 clock_freq_hz = VCPU_STALL_DEFAULT_CLOCK_HZ;
> +	u32 stall_timeout_sec = VCPU_STALL_DEFAULT_TIMEOUT_SEC;
> +
> +	vcpu_stall = kzalloc(sizeof(struct vcpu_stall), GFP_KERNEL);
> +	if (!vcpu_stall) {
> +		ret = -ENOMEM;
> +		goto err;
> +	}
> +	vdev->priv = vcpu_stall;
> +
> +	vcpu_stall->priv = devm_alloc_percpu(&vdev->dev,
> +					typeof(struct vcpu_stall_priv));
> +	if (!vcpu_stall->priv) {
> +		ret = -ENOMEM;
> +		goto failed_priv;
> +	}
> +
> +	for_each_possible_cpu(cpu) {
> +		struct vcpu_stall_priv *priv;
> +
> +		priv = per_cpu_ptr(vcpu_stall->priv, cpu);
> +		priv->vdev = vdev;
> +	}
> +
> +	ret = virtio_cread_feature(vdev, VCPU_STALL_REG_CLOCK_FREQ_HZ,
> +						struct vcpu_stall_detect_config, clock_freq_hz,
> +						&clock_freq_hz);
> +	if (ret || !clock_freq_hz) {
> +		if (!(clock_freq_hz > 0 &&
> +		      clock_freq_hz < VCPU_STALL_MAX_CLOCK_HZ)) {
> +			dev_warn(&vdev->dev, "clk out of range\n");
> +			clock_freq_hz = VCPU_STALL_DEFAULT_CLOCK_HZ;
> +		}
> +	}
> +	ret = virtio_cread_feature(vdev, VCPU_STALL_REG_TIMEOUT_SEC,
> +						struct vcpu_stall_detect_config, stall_timeout_sec,
> +						&stall_timeout_sec);
> +	if (ret || !stall_timeout_sec) {
> +		if (!(stall_timeout_sec > 0 &&
> +		      stall_timeout_sec < VCPU_STALL_MAX_TIMEOUT_SEC)) {
> +			dev_warn(&vdev->dev, "stall timeout out of range\n");
> +			stall_timeout_sec = VCPU_STALL_DEFAULT_TIMEOUT_SEC;

how does host know what is the range?

> +		}
> +	}
> +
> +	vcpu_stall_config = (struct vcpu_stall_detect_config) {
> +		.clock_freq_hz		= clock_freq_hz,
> +		.stall_timeout_sec	= stall_timeout_sec
> +	};
> +
> +	/* find virtqueue for guest to send pet event to host */
> +	vcpu_stall->vq = virtio_find_single_vq(vdev, NULL, "pet-event");
> +	if (IS_ERR(vcpu_stall->vq)) {
> +		dev_err(&vdev->dev, "failed to find vq\n");
> +		goto failed_priv;
> +	}
> +
> +	spin_lock_init(&vcpu_stall->lock);
> +
> +	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(&vdev->dev, "failed to install cpu hotplug\n");
> +		goto failed_priv;
> +	}
> +
> +	vcpu_stall_config.hp_online = ret;
> +	return 0;
> +
> +
> +failed_priv:
> +	kfree(vcpu_stall);
> +err:
> +	return ret;
> +}
> +
> +static void vcpu_stall_detect_remove(struct virtio_device *vdev)
> +{
> +	int cpu;
> +
> +	cpuhp_remove_state(vcpu_stall_config.hp_online);
> +
> +	for_each_possible_cpu(cpu)
> +		stop_stall_detector_cpu(cpu);


you are sending a bunch of messages ok but never even
wait for them to be processed. normally there's
need to reset device, destroy vqs ... not necessary here? why?

> +}
> +
> +static unsigned int features_legacy[] = {
> +	VCPU_STALL_REG_STATUS, VCPU_STALL_REG_LOAD_CNT, VCPU_STALL_REG_CURRENT_CNT,
> +	VCPU_STALL_REG_CLOCK_FREQ_HZ, VCPU_STALL_REG_LEN, VCPU_STALL_REG_TIMEOUT_SEC
> +};
> +


this should be a modern only device, no way this needs legacy support.


> +
> +static unsigned int features[] = {
> +	VCPU_STALL_REG_STATUS, VCPU_STALL_REG_LOAD_CNT, VCPU_STALL_REG_CURRENT_CNT,
> +	VCPU_STALL_REG_CLOCK_FREQ_HZ, VCPU_STALL_REG_LEN, VCPU_STALL_REG_TIMEOUT_SEC
> +};
> +
> +static struct virtio_driver vcpu_stall_detect_driver = {
> +	.feature_table	= features,
> +	.feature_table_size = ARRAY_SIZE(features),
> +	.feature_table_legacy	= features_legacy,
> +	.feature_table_size_legacy	= ARRAY_SIZE(features_legacy),
> +	.driver.name	= KBUILD_MODNAME,
> +	.driver.owner	= THIS_MODULE,
> +	.id_table =	vcpu_stall_id_table,
> +	.probe  = vcpu_stall_detect_probe,
> +	.remove = vcpu_stall_detect_remove,
> +};
> +
> +module_virtio_driver(vcpu_stall_detect_driver);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_DEVICE_TABLE(virtio, vcpu_stall_id_table);
> +MODULE_AUTHOR("zhanghao1 <zhanghao1@kylinos.cn>");
> +MODULE_DESCRIPTION("VCPU stall detector");
> -- 
> 2.25.1
> 
> 
> No virus found
> 		Checked by Hillstone Network AntiVirus

On Mon, 31 Jul 2023 09:25:12 +0800, "zhanghao1" <zhanghao1@kylinos.cn> wrote:
> A new virtio pci driver is added for listening to vcpus
> inside guest. Each vcpu creates a corresponding thread to
> periodically send data to qemu's back-end watchdog device.
> If a vCPU is in the stall state, data cannot be sent to
> back-end virtio device. As a result, the back-end device
> can detect that the guest is in the stall state.
>
> The driver is mainly used with the back-end watchdog device of qemu.
>
> The qemu backend watchdog device is implemented as follow:
> https://lore.kernel.org/qemu-devel/20230705081813.411526-1-zhanghao1@kylinos.cn/


I think we need to introduce this new device to the virtio spec firstly.

Thanks.


>
> Signed-off-by: zhanghao1 <zhanghao1@kylinos.cn>
> ---
>  drivers/virtio/Kconfig                      |   9 +
>  drivers/virtio/Makefile                     |   1 +
>  drivers/virtio/virtio_vcpu_stall_detector.c | 299 ++++++++++++++++++++
>  3 files changed, 309 insertions(+)
>  create mode 100644 drivers/virtio/virtio_vcpu_stall_detector.c
>
> diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> index 0a53a61231c2..869323e345a1 100644
> --- a/drivers/virtio/Kconfig
> +++ b/drivers/virtio/Kconfig
> @@ -173,4 +173,13 @@ config VIRTIO_DMA_SHARED_BUFFER
>  	 This option adds a flavor of dma buffers that are backed by
>  	 virtio resources.
>
> +config VIRTIO_VCPU_WATCHDOG
> +	tristate "Virtio vcpu watchdog driver"
> +	depends on VIRTIO_PCI
> +	help
> +	 When this driver is bound inside a KVM guest, it will
> +	 periodically "pet" an PCI virtio watchdog device from each vCPU
> +	 and allow the host to detect vCPU stalls.
> +
> +	 If you do not intend to run this kernel as a guest, say N.
>  endif # VIRTIO_MENU
> diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
> index 8e98d24917cc..c7341f078a34 100644
> --- a/drivers/virtio/Makefile
> +++ b/drivers/virtio/Makefile
> @@ -12,3 +12,4 @@ obj-$(CONFIG_VIRTIO_INPUT) += virtio_input.o
>  obj-$(CONFIG_VIRTIO_VDPA) += virtio_vdpa.o
>  obj-$(CONFIG_VIRTIO_MEM) += virtio_mem.o
>  obj-$(CONFIG_VIRTIO_DMA_SHARED_BUFFER) += virtio_dma_buf.o
> +obj-$(CONFIG_VIRTIO_VCPU_WATCHDOG) += virtio_vcpu_stall_detector.o
> diff --git a/drivers/virtio/virtio_vcpu_stall_detector.c b/drivers/virtio/virtio_vcpu_stall_detector.c
> new file mode 100644
> index 000000000000..58344ca528be
> --- /dev/null
> +++ b/drivers/virtio/virtio_vcpu_stall_detector.c
> @@ -0,0 +1,299 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +//
> +// VCPU stall detector.
> +// Copyright (C) Kylin Software, 2023
> +
> +#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 <uapi/linux/virtio_ids.h>
> +#include <linux/virtio_config.h>
> +#include <linux/param.h>
> +#include <linux/percpu.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_REG_TIMEOUT_SEC	(0x14)
> +
> +#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;
> +
> +	enum cpuhp_state hp_online;
> +};
> +
> +struct vcpu_stall_priv {
> +	struct hrtimer vcpu_hrtimer;
> +	struct virtio_device *vdev;
> +	u32 cpu_id;
> +};
> +
> +struct vcpu_stall {
> +	struct vcpu_stall_priv *priv;
> +	struct virtqueue *vq;
> +	spinlock_t lock;
> +	struct pet_event {
> +		u32 cpu_id;
> +		bool is_initialized;
> +		u32 ticks;
> +	} pet_event;
> +};
> +
> +static const struct virtio_device_id vcpu_stall_id_table[] = {
> +	{ VIRTIO_ID_WATCHDOG, VIRTIO_DEV_ANY_ID },
> +	{ 0, },
> +};
> +
> +/* The vcpu stall configuration structure which applies to all the CPUs */
> +static struct vcpu_stall_detect_config vcpu_stall_config;
> +static struct vcpu_stall *vcpu_stall;
> +
> +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;
> +	struct scatterlist sg;
> +	int unused, err = 0;
> +
> +	struct vcpu_stall_priv *vcpu_stall_detector =
> +		this_cpu_ptr(vcpu_stall->priv);
> +
> +	/* 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;
> +
> +	spin_lock(&vcpu_stall->lock);
> +	while (virtqueue_get_buf(vcpu_stall->vq, &unused))
> +		;
> +	vcpu_stall->pet_event.ticks = cpu_to_virtio32(vcpu_stall_detector->vdev, ticks);
> +	vcpu_stall->pet_event.is_initialized = true;
> +	vcpu_stall->pet_event.cpu_id = vcpu_stall_detector->cpu_id;
> +
> +	sg_init_one(&sg, &vcpu_stall->pet_event, sizeof(vcpu_stall->pet_event));
> +	err = virtqueue_add_outbuf(vcpu_stall->vq, &sg, 1, vcpu_stall, GFP_ATOMIC);
> +	if (!err)
> +		virtqueue_kick(vcpu_stall->vq);
> +	else
> +		pr_err("cpu:%d failed to add outbuf, err:%d\n", vcpu_stall_detector->cpu_id, err);
> +
> +	spin_unlock(&vcpu_stall->lock);
> +
> +	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 scatterlist sg;
> +	struct hrtimer *vcpu_hrtimer;
> +	int err = 0;
> +
> +	struct vcpu_stall_priv *vcpu_stall_detector =
> +		this_cpu_ptr(vcpu_stall->priv);
> +
> +	vcpu_stall_detector->cpu_id = cpu;
> +
> +	vcpu_hrtimer = &vcpu_stall_detector->vcpu_hrtimer;
> +
> +	/* 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->pet_event.ticks = cpu_to_virtio32(vcpu_stall_detector->vdev, ticks);
> +
> +	/* 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->pet_event.is_initialized = true;
> +
> +	spin_lock(&vcpu_stall->lock);
> +	vcpu_stall->pet_event.cpu_id = cpu;
> +	sg_init_one(&sg, &vcpu_stall->pet_event, sizeof(vcpu_stall->pet_event));
> +	err = virtqueue_add_outbuf(vcpu_stall->vq, &sg, 1, vcpu_stall, GFP_ATOMIC);
> +	if (!err)
> +		virtqueue_kick(vcpu_stall->vq);
> +
> +	spin_unlock(&vcpu_stall->lock);
> +
> +	hrtimer_start(vcpu_hrtimer, ms_to_ktime(ping_timeout_ms),
> +		      HRTIMER_MODE_REL_PINNED);
> +	return err;
> +}
> +
> +static int stop_stall_detector_cpu(unsigned int cpu)
> +{
> +	int err = 0;
> +	struct scatterlist sg;
> +
> +	struct vcpu_stall_priv *vcpu_stall_detector =
> +		per_cpu_ptr(vcpu_stall_detectors, cpu);
> +
> +	/* Disable the stall detector for the current CPU */
> +	hrtimer_cancel(&vcpu_stall_detector->vcpu_hrtimer);
> +	vcpu_stall->pet_event.is_initialized = false;
> +	vcpu_stall->pet_event.cpu_id = cpu;
> +
> +	spin_lock(&vcpu_stall->lock);
> +	sg_init_one(&sg, &vcpu_stall->pet_event, sizeof(vcpu_stall->pet_event));
> +	err = virtqueue_add_outbuf(vcpu_stall->vq, &sg, 1, vcpu_stall, GFP_ATOMIC);
> +	if (!err)
> +		virtqueue_kick(vcpu_stall->vq);
> +
> +	spin_unlock(&vcpu_stall->lock);
> +
> +	return err;
> +}
> +
> +static int vcpu_stall_detect_probe(struct virtio_device *vdev)
> +{
> +	int ret, cpu;
> +	u32 clock_freq_hz = VCPU_STALL_DEFAULT_CLOCK_HZ;
> +	u32 stall_timeout_sec = VCPU_STALL_DEFAULT_TIMEOUT_SEC;
> +
> +	vcpu_stall = kzalloc(sizeof(struct vcpu_stall), GFP_KERNEL);
> +	if (!vcpu_stall) {
> +		ret = -ENOMEM;
> +		goto err;
> +	}
> +	vdev->priv = vcpu_stall;
> +
> +	vcpu_stall->priv = devm_alloc_percpu(&vdev->dev,
> +					typeof(struct vcpu_stall_priv));
> +	if (!vcpu_stall->priv) {
> +		ret = -ENOMEM;
> +		goto failed_priv;
> +	}
> +
> +	for_each_possible_cpu(cpu) {
> +		struct vcpu_stall_priv *priv;
> +
> +		priv = per_cpu_ptr(vcpu_stall->priv, cpu);
> +		priv->vdev = vdev;
> +	}
> +
> +	ret = virtio_cread_feature(vdev, VCPU_STALL_REG_CLOCK_FREQ_HZ,
> +						struct vcpu_stall_detect_config, clock_freq_hz,
> +						&clock_freq_hz);
> +	if (ret || !clock_freq_hz) {
> +		if (!(clock_freq_hz > 0 &&
> +		      clock_freq_hz < VCPU_STALL_MAX_CLOCK_HZ)) {
> +			dev_warn(&vdev->dev, "clk out of range\n");
> +			clock_freq_hz = VCPU_STALL_DEFAULT_CLOCK_HZ;
> +		}
> +	}
> +	ret = virtio_cread_feature(vdev, VCPU_STALL_REG_TIMEOUT_SEC,
> +						struct vcpu_stall_detect_config, stall_timeout_sec,
> +						&stall_timeout_sec);
> +	if (ret || !stall_timeout_sec) {
> +		if (!(stall_timeout_sec > 0 &&
> +		      stall_timeout_sec < VCPU_STALL_MAX_TIMEOUT_SEC)) {
> +			dev_warn(&vdev->dev, "stall timeout out of range\n");
> +			stall_timeout_sec = VCPU_STALL_DEFAULT_TIMEOUT_SEC;
> +		}
> +	}
> +
> +	vcpu_stall_config = (struct vcpu_stall_detect_config) {
> +		.clock_freq_hz		= clock_freq_hz,
> +		.stall_timeout_sec	= stall_timeout_sec
> +	};
> +
> +	/* find virtqueue for guest to send pet event to host */
> +	vcpu_stall->vq = virtio_find_single_vq(vdev, NULL, "pet-event");
> +	if (IS_ERR(vcpu_stall->vq)) {
> +		dev_err(&vdev->dev, "failed to find vq\n");
> +		goto failed_priv;
> +	}
> +
> +	spin_lock_init(&vcpu_stall->lock);
> +
> +	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(&vdev->dev, "failed to install cpu hotplug\n");
> +		goto failed_priv;
> +	}
> +
> +	vcpu_stall_config.hp_online = ret;
> +	return 0;
> +
> +
> +failed_priv:
> +	kfree(vcpu_stall);
> +err:
> +	return ret;
> +}
> +
> +static void vcpu_stall_detect_remove(struct virtio_device *vdev)
> +{
> +	int cpu;
> +
> +	cpuhp_remove_state(vcpu_stall_config.hp_online);
> +
> +	for_each_possible_cpu(cpu)
> +		stop_stall_detector_cpu(cpu);
> +}
> +
> +static unsigned int features_legacy[] = {
> +	VCPU_STALL_REG_STATUS, VCPU_STALL_REG_LOAD_CNT, VCPU_STALL_REG_CURRENT_CNT,
> +	VCPU_STALL_REG_CLOCK_FREQ_HZ, VCPU_STALL_REG_LEN, VCPU_STALL_REG_TIMEOUT_SEC
> +};
> +
> +
> +static unsigned int features[] = {
> +	VCPU_STALL_REG_STATUS, VCPU_STALL_REG_LOAD_CNT, VCPU_STALL_REG_CURRENT_CNT,
> +	VCPU_STALL_REG_CLOCK_FREQ_HZ, VCPU_STALL_REG_LEN, VCPU_STALL_REG_TIMEOUT_SEC
> +};
> +
> +static struct virtio_driver vcpu_stall_detect_driver = {
> +	.feature_table	= features,
> +	.feature_table_size = ARRAY_SIZE(features),
> +	.feature_table_legacy	= features_legacy,
> +	.feature_table_size_legacy	= ARRAY_SIZE(features_legacy),
> +	.driver.name	= KBUILD_MODNAME,
> +	.driver.owner	= THIS_MODULE,
> +	.id_table =	vcpu_stall_id_table,
> +	.probe  = vcpu_stall_detect_probe,
> +	.remove = vcpu_stall_detect_remove,
> +};
> +
> +module_virtio_driver(vcpu_stall_detect_driver);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_DEVICE_TABLE(virtio, vcpu_stall_id_table);
> +MODULE_AUTHOR("zhanghao1 <zhanghao1@kylinos.cn>");
> +MODULE_DESCRIPTION("VCPU stall detector");
> --
> 2.25.1
>
>
> No virus found
> 		Checked by Hillstone Network AntiVirus

Hi--

On 7/30/23 18:25, zhanghao1 wrote:
> A new virtio pci driver is added for listening to vcpus
> inside guest. Each vcpu creates a corresponding thread to
> periodically send data to qemu's back-end watchdog device.
> If a vCPU is in the stall state, data cannot be sent to
> back-end virtio device. As a result, the back-end device
> can detect that the guest is in the stall state.
> 
> The driver is mainly used with the back-end watchdog device of qemu.
> 
> The qemu backend watchdog device is implemented as follow:
> https://lore.kernel.org/qemu-devel/20230705081813.411526-1-zhanghao1@kylinos.cn/
> 
> Signed-off-by: zhanghao1 <zhanghao1@kylinos.cn>
> ---
>  drivers/virtio/Kconfig                      |   9 +
>  drivers/virtio/Makefile                     |   1 +
>  drivers/virtio/virtio_vcpu_stall_detector.c | 299 ++++++++++++++++++++
>  3 files changed, 309 insertions(+)
>  create mode 100644 drivers/virtio/virtio_vcpu_stall_detector.c
> 
> diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> index 0a53a61231c2..869323e345a1 100644
> --- a/drivers/virtio/Kconfig
> +++ b/drivers/virtio/Kconfig
> @@ -173,4 +173,13 @@ config VIRTIO_DMA_SHARED_BUFFER
>  	 This option adds a flavor of dma buffers that are backed by
>  	 virtio resources.
>  
> +config VIRTIO_VCPU_WATCHDOG
> +	tristate "Virtio vcpu watchdog driver"
> +	depends on VIRTIO_PCI
> +	help
> +	 When this driver is bound inside a KVM guest, it will
> +	 periodically "pet" an PCI virtio watchdog device from each vCPU

	                    a PCI

> +	 and allow the host to detect vCPU stalls.
> +
> +	 If you do not intend to run this kernel as a guest, say N.

Kconfig help text should be indented with one tab + 2 spaces
according to coding-style.rst.

>  endif # VIRTIO_MENU
> diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
> index 8e98d24917cc..c7341f078a34 100644
> --- a/drivers/virtio/Makefile
> +++ b/drivers/virtio/Makefile
> @@ -12,3 +12,4 @@ obj-$(CONFIG_VIRTIO_INPUT) += virtio_input.o
>  obj-$(CONFIG_VIRTIO_VDPA) += virtio_vdpa.o
>  obj-$(CONFIG_VIRTIO_MEM) += virtio_mem.o
>  obj-$(CONFIG_VIRTIO_DMA_SHARED_BUFFER) += virtio_dma_buf.o
> +obj-$(CONFIG_VIRTIO_VCPU_WATCHDOG) += virtio_vcpu_stall_detector.o
> diff --git a/drivers/virtio/virtio_vcpu_stall_detector.c b/drivers/virtio/virtio_vcpu_stall_detector.c
> new file mode 100644
> index 000000000000..58344ca528be
> --- /dev/null
> +++ b/drivers/virtio/virtio_vcpu_stall_detector.c
> @@ -0,0 +1,299 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +//
> +// VCPU stall detector.
> +// Copyright (C) Kylin Software, 2023
> +
> +#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 <uapi/linux/virtio_ids.h>
> +#include <linux/virtio_config.h>
> +#include <linux/param.h>
> +#include <linux/percpu.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_REG_TIMEOUT_SEC	(0x14)
> +
> +#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;
> +
> +	enum cpuhp_state hp_online;
> +};
> +
> +struct vcpu_stall_priv {
> +	struct hrtimer vcpu_hrtimer;
> +	struct virtio_device *vdev;
> +	u32 cpu_id;
> +};
> +
> +struct vcpu_stall {
> +	struct vcpu_stall_priv *priv;
> +	struct virtqueue *vq;
> +	spinlock_t lock;
> +	struct pet_event {
> +		u32 cpu_id;
> +		bool is_initialized;
> +		u32 ticks;
> +	} pet_event;
> +};
> +
> +static const struct virtio_device_id vcpu_stall_id_table[] = {
> +	{ VIRTIO_ID_WATCHDOG, VIRTIO_DEV_ANY_ID },
> +	{ 0, },
> +};
> +
> +/* The vcpu stall configuration structure which applies to all the CPUs */
> +static struct vcpu_stall_detect_config vcpu_stall_config;
> +static struct vcpu_stall *vcpu_stall;
> +
> +static struct vcpu_stall_priv __percpu *vcpu_stall_detectors;
> +
> +static enum hrtimer_restart
> +vcpu_stall_detect_timer_fn(struct hrtimer *hrtimer)

One line instead of the 2 lines above.

> +{

-- 
~Randy