Message-Id: <20230731012512.235085-1-zhanghao1@kylinos.cn>
Date:   Mon, 31 Jul 2023 09:25:12 +0800
From:   zhanghao1 <zhanghao1@...inos.cn>
To:     virtualization@...ts.linux-foundation.org
Cc:     mst@...hat.com, jasowang@...hat.com, xuanzhuo@...ux.alibaba.com,
        linux-kernel@...r.kernel.org, zhanghao1 <zhanghao1@...inos.cn>
Subject: [PATCH] virtio: a new vcpu watchdog driver

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@...inos.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@...inos.cn>");
+MODULE_DESCRIPTION("VCPU stall detector");
-- 
2.25.1


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