[PATCH 2/2] vfio/mtty: Enable migration support

[Alex Williamson]

The mtty driver exposes a PCI serial device to userspace and therefore
makes an easy target for a sample device supporting migration.  The device
does not make use of DMA, therefore we can easily claim support for the
migration P2P states, as well as dirty logging.  This implementation also
makes use of PRE_COPY support in order to provide migration stream
compatibility testing, which should generally be considered good practice.

Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
---

Much of this should look familiar to vfio-pci variant driver developers
;)

 samples/vfio-mdev/mtty.c | 582 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 582 insertions(+)

diff --git a/samples/vfio-mdev/mtty.c b/samples/vfio-mdev/mtty.c
index 0a2760818e46..572f51342fbd 100644
--- a/samples/vfio-mdev/mtty.c
+++ b/samples/vfio-mdev/mtty.c
@@ -29,6 +29,8 @@
 #include <linux/serial.h>
 #include <uapi/linux/serial_reg.h>
 #include <linux/eventfd.h>
+#include <linux/anon_inodes.h>
+
 /*
  * #defines
  */
@@ -124,6 +126,29 @@ struct serial_port {
 	u8 intr_trigger_level;  /* interrupt trigger level */
 };
 
+struct mtty_data {
+	u64 magic;
+#define MTTY_MAGIC 0x7e9d09898c3e2c4e /* Nothing clever, just random */
+	u32 major_ver;
+#define MTTY_MAJOR_VER 1
+	u32 minor_ver;
+#define MTTY_MINOR_VER 0
+	u32 nr_ports;
+	u32 flags;
+	struct serial_port ports[2];
+};
+
+struct mdev_state;
+
+struct mtty_migration_file {
+	struct file *filp;
+	struct mutex lock;
+	struct mdev_state *mdev_state;
+	struct mtty_data data;
+	ssize_t filled_size;
+	u8 disabled:1;
+};
+
 /* State of each mdev device */
 struct mdev_state {
 	struct vfio_device vdev;
@@ -140,6 +165,12 @@ struct mdev_state {
 	struct mutex rxtx_lock;
 	struct vfio_device_info dev_info;
 	int nr_ports;
+	struct mutex state_mutex;
+	enum vfio_device_mig_state state;
+	struct mutex reset_mutex;
+	struct mtty_migration_file *saving_migf;
+	struct mtty_migration_file *resuming_migf;
+	u8 deferred_reset:1;
 };
 
 static struct mtty_type {
@@ -716,6 +747,534 @@ static ssize_t mdev_access(struct mdev_state *mdev_state, u8 *buf, size_t count,
 	return ret;
 }
 
+static void mtty_disable_file(struct mtty_migration_file *migf)
+{
+	mutex_lock(&migf->lock);
+	migf->disabled = true;
+	migf->filled_size = 0;
+	migf->filp->f_pos = 0;
+	mutex_unlock(&migf->lock);
+}
+
+static void mtty_disable_files(struct mdev_state *mdev_state)
+{
+	if (mdev_state->saving_migf) {
+		mtty_disable_file(mdev_state->saving_migf);
+		fput(mdev_state->saving_migf->filp);
+		mdev_state->saving_migf = NULL;
+	}
+
+	if (mdev_state->resuming_migf) {
+		mtty_disable_file(mdev_state->resuming_migf);
+		fput(mdev_state->resuming_migf->filp);
+		mdev_state->resuming_migf = NULL;
+	}
+}
+
+static void mtty_state_mutex_unlock(struct mdev_state *mdev_state)
+{
+again:
+	mutex_lock(&mdev_state->reset_mutex);
+	if (mdev_state->deferred_reset) {
+		mdev_state->deferred_reset = false;
+		mutex_unlock(&mdev_state->reset_mutex);
+		mdev_state->state = VFIO_DEVICE_STATE_RUNNING;
+		mtty_disable_files(mdev_state);
+		goto again;
+	}
+	mutex_unlock(&mdev_state->state_mutex);
+	mutex_unlock(&mdev_state->reset_mutex);
+}
+
+static int mtty_release_migf(struct inode *inode, struct file *filp)
+{
+	struct mtty_migration_file *migf = filp->private_data;
+
+	mtty_disable_file(migf);
+	mutex_destroy(&migf->lock);
+	kfree(migf);
+
+	return 0;
+}
+
+static long mtty_precopy_ioctl(struct file *filp, unsigned int cmd,
+			       unsigned long arg)
+{
+	struct mtty_migration_file *migf = filp->private_data;
+	struct mdev_state *mdev_state = migf->mdev_state;
+	loff_t *pos = &filp->f_pos;
+	struct vfio_precopy_info info = {};
+	unsigned long minsz;
+	int ret;
+
+	if (cmd != VFIO_MIG_GET_PRECOPY_INFO)
+		return -ENOTTY;
+
+	minsz = offsetofend(struct vfio_precopy_info, dirty_bytes);
+
+	if (copy_from_user(&info, (void __user *)arg, minsz))
+		return -EFAULT;
+	if (info.argsz < minsz)
+		return -EINVAL;
+
+	mutex_lock(&mdev_state->state_mutex);
+	if (mdev_state->state != VFIO_DEVICE_STATE_PRE_COPY &&
+	    mdev_state->state != VFIO_DEVICE_STATE_PRE_COPY_P2P) {
+		ret = -EINVAL;
+		goto unlock;
+	}
+
+	mutex_lock(&migf->lock);
+
+	if (migf->disabled) {
+		mutex_unlock(&migf->lock);
+		ret = -ENODEV;
+		goto unlock;
+	}
+
+	if (*pos > migf->filled_size) {
+		mutex_unlock(&migf->lock);
+		ret = -EINVAL;
+		goto unlock;
+	}
+
+	info.dirty_bytes = 0;
+	info.initial_bytes = migf->filled_size - *pos;
+	mutex_unlock(&migf->lock);
+
+	ret = copy_to_user((void __user *)arg, &info, minsz) ? -EFAULT : 0;
+unlock:
+	mtty_state_mutex_unlock(mdev_state);
+	return ret;
+}
+
+static ssize_t mtty_save_read(struct file *filp, char __user *buf,
+			      size_t len, loff_t *pos)
+{
+	struct mtty_migration_file *migf = filp->private_data;
+	ssize_t ret = 0;
+
+	if (pos)
+		return -ESPIPE;
+
+	pos = &filp->f_pos;
+
+	mutex_lock(&migf->lock);
+
+	dev_dbg(migf->mdev_state->vdev.dev, "%s ask %zu\n", __func__, len);
+
+	if (migf->disabled) {
+		ret = -ENODEV;
+		goto out_unlock;
+	}
+
+	if (*pos > migf->filled_size) {
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
+	len = min_t(size_t, migf->filled_size - *pos, len);
+	if (len) {
+		if (copy_to_user(buf, (void *)&migf->data + *pos, len)) {
+			ret = -EFAULT;
+			goto out_unlock;
+		}
+		*pos += len;
+		ret = len;
+	}
+out_unlock:
+	dev_dbg(migf->mdev_state->vdev.dev, "%s read %zu\n", __func__, ret);
+	mutex_unlock(&migf->lock);
+	return ret;
+}
+
+static const struct file_operations mtty_save_fops = {
+	.owner = THIS_MODULE,
+	.read = mtty_save_read,
+	.unlocked_ioctl = mtty_precopy_ioctl,
+	.compat_ioctl = compat_ptr_ioctl,
+	.release = mtty_release_migf,
+	.llseek = no_llseek,
+};
+
+static struct mtty_migration_file *
+mtty_save_device_data(struct mdev_state *mdev_state,
+		      enum vfio_device_mig_state state)
+{
+	struct mtty_migration_file *migf = mdev_state->saving_migf;
+	struct mtty_migration_file *ret = NULL;
+
+	if (migf) {
+		if (state == VFIO_DEVICE_STATE_STOP_COPY)
+			goto fill_data;
+		return ret;
+	}
+
+	migf = kzalloc(sizeof(*migf), GFP_KERNEL_ACCOUNT);
+	if (!migf)
+		return ERR_PTR(-ENOMEM);
+
+	migf->filp = anon_inode_getfile("mtty_mig", &mtty_save_fops,
+					migf, O_RDONLY);
+	if (IS_ERR(migf->filp)) {
+		int rc = PTR_ERR(migf->filp);
+
+		kfree(migf);
+		return ERR_PTR(rc);
+	}
+
+	stream_open(migf->filp->f_inode, migf->filp);
+	mutex_init(&migf->lock);
+	migf->mdev_state = mdev_state;
+
+	migf->data.magic = MTTY_MAGIC;
+	migf->data.major_ver = MTTY_MAJOR_VER;
+	migf->data.minor_ver = MTTY_MINOR_VER;
+	migf->data.nr_ports = mdev_state->nr_ports;
+
+	migf->filled_size = offsetof(struct mtty_data, ports);
+
+	dev_dbg(mdev_state->vdev.dev, "%s filled header to %zu\n",
+		__func__, migf->filled_size);
+
+	ret = mdev_state->saving_migf = migf;
+
+fill_data:
+	if (state == VFIO_DEVICE_STATE_STOP_COPY) {
+		int i;
+
+		mutex_lock(&migf->lock);
+		for (i = 0; i < mdev_state->nr_ports; i++) {
+			memcpy(&migf->data.ports[i],
+			       &mdev_state->s[i], sizeof(struct serial_port));
+			migf->filled_size += sizeof(struct serial_port);
+		}
+		dev_dbg(mdev_state->vdev.dev, "%s filled to %zu\n",
+			__func__, migf->filled_size);
+		mutex_unlock(&migf->lock);
+	}
+
+	return ret;
+}
+
+static ssize_t mtty_resume_write(struct file *filp, const char __user *buf,
+				 size_t len, loff_t *pos)
+{
+	struct mtty_migration_file *migf = filp->private_data;
+	loff_t requested_length;
+	ssize_t ret = 0;
+
+	if (pos)
+		return -ESPIPE;
+
+	pos = &filp->f_pos;
+
+	if (*pos < 0 ||
+	    check_add_overflow((loff_t)len, *pos, &requested_length))
+		return -EINVAL;
+
+	if (requested_length > sizeof(struct mtty_data))
+		return -ENOMEM;
+
+	mutex_lock(&migf->lock);
+
+	if (migf->disabled) {
+		ret = -ENODEV;
+		goto out_unlock;
+	}
+
+	if (copy_from_user((void *)&migf->data + *pos, buf, len)) {
+		ret = -EFAULT;
+		goto out_unlock;
+	}
+
+	*pos += len;
+	ret = len;
+	migf->filled_size += len;
+
+	dev_dbg(migf->mdev_state->vdev.dev, "%s received %zu, total %zu\n",
+		__func__, len, migf->filled_size);
+
+	if (migf->filled_size >= offsetof(struct mtty_data, ports)) {
+		struct mdev_state *mdev_state = migf->mdev_state;
+
+		if (migf->data.magic != MTTY_MAGIC || migf->data.flags ||
+		    migf->data.major_ver != MTTY_MAJOR_VER ||
+		    migf->data.minor_ver != MTTY_MINOR_VER ||
+		    migf->data.nr_ports != mdev_state->nr_ports) {
+			dev_dbg(migf->mdev_state->vdev.dev,
+				"%s failed validation\n", __func__);
+			ret = -EFAULT;
+		} else {
+			dev_dbg(migf->mdev_state->vdev.dev,
+				"%s header validated\n", __func__);
+		}
+	}
+
+out_unlock:
+	mutex_unlock(&migf->lock);
+	return ret;
+}
+
+static const struct file_operations mtty_resume_fops = {
+	.owner = THIS_MODULE,
+	.write = mtty_resume_write,
+	.release = mtty_release_migf,
+	.llseek = no_llseek,
+};
+
+static struct mtty_migration_file *
+mtty_resume_device_data(struct mdev_state *mdev_state)
+{
+	struct mtty_migration_file *migf;
+	int ret;
+
+	migf = kzalloc(sizeof(*migf), GFP_KERNEL_ACCOUNT);
+	if (!migf)
+		return ERR_PTR(-ENOMEM);
+
+	migf->filp = anon_inode_getfile("mtty_mig", &mtty_resume_fops,
+					migf, O_WRONLY);
+	if (IS_ERR(migf->filp)) {
+		ret = PTR_ERR(migf->filp);
+		kfree(migf);
+		return ERR_PTR(ret);
+	}
+
+	stream_open(migf->filp->f_inode, migf->filp);
+	mutex_init(&migf->lock);
+	migf->mdev_state = mdev_state;
+
+	mdev_state->resuming_migf = migf;
+
+	return migf;
+}
+
+static int mtty_load_state(struct mdev_state *mdev_state)
+{
+	struct mtty_migration_file *migf = mdev_state->resuming_migf;
+	int i;
+
+	mutex_lock(&migf->lock);
+	/* magic and version already tested by resume write fn */
+	if (migf->filled_size < offsetof(struct mtty_data, ports) +
+			(mdev_state->nr_ports * sizeof(struct serial_port))) {
+		dev_dbg(mdev_state->vdev.dev, "%s expected %zu, got %zu\n",
+			__func__, offsetof(struct mtty_data, ports) +
+			(mdev_state->nr_ports * sizeof(struct serial_port)),
+			migf->filled_size);
+		mutex_unlock(&migf->lock);
+		return -EINVAL;
+	}
+
+	for (i = 0; i < mdev_state->nr_ports; i++)
+		memcpy(&mdev_state->s[i],
+		       &migf->data.ports[i], sizeof(struct serial_port));
+
+	mutex_unlock(&migf->lock);
+	return 0;
+}
+
+static struct file *mtty_step_state(struct mdev_state *mdev_state,
+				     enum vfio_device_mig_state new)
+{
+	enum vfio_device_mig_state cur = mdev_state->state;
+
+	dev_dbg(mdev_state->vdev.dev, "%s: %d -> %d\n", __func__, cur, new);
+
+	/*
+	 * The following state transitions are no-op considering
+	 * mtty does not do DMA nor require any explicit start/stop.
+	 *
+	 *         RUNNING -> RUNNING_P2P
+	 *         RUNNING_P2P -> RUNNING
+	 *         RUNNING_P2P -> STOP
+	 *         PRE_COPY -> PRE_COPY_P2P
+	 *         PRE_COPY_P2P -> PRE_COPY
+	 *         STOP -> RUNNING_P2P
+	 */
+	if ((cur == VFIO_DEVICE_STATE_RUNNING &&
+	     new == VFIO_DEVICE_STATE_RUNNING_P2P) ||
+	    (cur == VFIO_DEVICE_STATE_RUNNING_P2P &&
+	     (new == VFIO_DEVICE_STATE_RUNNING ||
+	      new == VFIO_DEVICE_STATE_STOP)) ||
+	    (cur == VFIO_DEVICE_STATE_PRE_COPY &&
+	     new == VFIO_DEVICE_STATE_PRE_COPY_P2P) ||
+	    (cur == VFIO_DEVICE_STATE_PRE_COPY_P2P &&
+	     new == VFIO_DEVICE_STATE_PRE_COPY) ||
+	    (cur == VFIO_DEVICE_STATE_STOP &&
+	     new == VFIO_DEVICE_STATE_RUNNING_P2P))
+		return NULL;
+
+	/*
+	 * The following state transitions simply close migration files,
+	 * with the exception of RESUMING -> STOP, which needs to load
+	 * the state first.
+	 *
+	 *         RESUMING -> STOP
+	 *         PRE_COPY -> RUNNING
+	 *         PRE_COPY_P2P -> RUNNING_P2P
+	 *         STOP_COPY -> STOP
+	 */
+	if (cur == VFIO_DEVICE_STATE_RESUMING &&
+	    new == VFIO_DEVICE_STATE_STOP) {
+		int ret;
+
+		ret = mtty_load_state(mdev_state);
+		if (ret)
+			return ERR_PTR(ret);
+		mtty_disable_files(mdev_state);
+		return NULL;
+	}
+
+	if ((cur == VFIO_DEVICE_STATE_PRE_COPY &&
+	     new == VFIO_DEVICE_STATE_RUNNING) ||
+	    (cur == VFIO_DEVICE_STATE_PRE_COPY_P2P &&
+	     new == VFIO_DEVICE_STATE_RUNNING_P2P) ||
+	    (cur == VFIO_DEVICE_STATE_STOP_COPY &&
+	     new == VFIO_DEVICE_STATE_STOP)) {
+		mtty_disable_files(mdev_state);
+		return NULL;
+	}
+
+	/*
+	 * The following state transitions return migration files.
+	 *
+	 *         RUNNING -> PRE_COPY
+	 *         RUNNING_P2P -> PRE_COPY_P2P
+	 *         STOP -> STOP_COPY
+	 *         STOP -> RESUMING
+	 *         PRE_COPY_P2P -> STOP_COPY
+	 */
+	if ((cur == VFIO_DEVICE_STATE_RUNNING &&
+	     new == VFIO_DEVICE_STATE_PRE_COPY) ||
+	    (cur == VFIO_DEVICE_STATE_RUNNING_P2P &&
+	     new == VFIO_DEVICE_STATE_PRE_COPY_P2P) ||
+	    (cur == VFIO_DEVICE_STATE_STOP &&
+	     new == VFIO_DEVICE_STATE_STOP_COPY) ||
+	    (cur == VFIO_DEVICE_STATE_PRE_COPY_P2P &&
+	     new == VFIO_DEVICE_STATE_STOP_COPY)) {
+		struct mtty_migration_file *migf;
+
+		migf = mtty_save_device_data(mdev_state, new);
+		if (IS_ERR(migf))
+			return ERR_CAST(migf);
+
+		if (migf) {
+			get_file(migf->filp);
+
+			return migf->filp;
+		}
+		return NULL;
+	}
+
+	if (cur == VFIO_DEVICE_STATE_STOP &&
+	    new == VFIO_DEVICE_STATE_RESUMING) {
+		struct mtty_migration_file *migf;
+
+		migf = mtty_resume_device_data(mdev_state);
+		if (IS_ERR(migf))
+			return ERR_CAST(migf);
+
+		get_file(migf->filp);
+
+		return migf->filp;
+	}
+
+	/* vfio_mig_get_next_state() does not use arcs other than the above */
+	WARN_ON(true);
+	return ERR_PTR(-EINVAL);
+}
+
+static struct file *mtty_set_state(struct vfio_device *vdev,
+				   enum vfio_device_mig_state new_state)
+{
+	struct mdev_state *mdev_state =
+		container_of(vdev, struct mdev_state, vdev);
+	struct file *ret = NULL;
+
+	dev_dbg(vdev->dev, "%s -> %d\n", __func__, new_state);
+
+	mutex_lock(&mdev_state->state_mutex);
+	while (mdev_state->state != new_state) {
+		enum vfio_device_mig_state next_state;
+		int rc = vfio_mig_get_next_state(vdev, mdev_state->state,
+						 new_state, &next_state);
+		if (rc) {
+			ret = ERR_PTR(rc);
+			break;
+		}
+
+		ret = mtty_step_state(mdev_state, next_state);
+		if (IS_ERR(ret))
+			break;
+
+		mdev_state->state = next_state;
+
+		if (WARN_ON(ret && new_state != next_state)) {
+			fput(ret);
+			ret = ERR_PTR(-EINVAL);
+			break;
+		}
+	}
+	mtty_state_mutex_unlock(mdev_state);
+	return ret;
+}
+
+static int mtty_get_state(struct vfio_device *vdev,
+			  enum vfio_device_mig_state *current_state)
+{
+	struct mdev_state *mdev_state =
+		container_of(vdev, struct mdev_state, vdev);
+
+	mutex_lock(&mdev_state->state_mutex);
+	*current_state = mdev_state->state;
+	mtty_state_mutex_unlock(mdev_state);
+	return 0;
+}
+
+static int mtty_get_data_size(struct vfio_device *vdev,
+			      unsigned long *stop_copy_length)
+{
+	struct mdev_state *mdev_state =
+		container_of(vdev, struct mdev_state, vdev);
+
+	*stop_copy_length = offsetof(struct mtty_data, ports) +
+			(mdev_state->nr_ports * sizeof(struct serial_port));
+	return 0;
+}
+
+static const struct vfio_migration_ops mtty_migration_ops = {
+	.migration_set_state = mtty_set_state,
+	.migration_get_state = mtty_get_state,
+	.migration_get_data_size = mtty_get_data_size,
+};
+
+static int mtty_log_start(struct vfio_device *vdev,
+			  struct rb_root_cached *ranges,
+			  u32 nnodes, u64 *page_size)
+{
+	return 0;
+}
+
+static int mtty_log_stop(struct vfio_device *vdev)
+{
+	return 0;
+}
+
+static int mtty_log_read_and_clear(struct vfio_device *vdev,
+				   unsigned long iova, unsigned long length,
+				   struct iova_bitmap *dirty)
+{
+	return 0;
+}
+
+static const struct vfio_log_ops mtty_log_ops = {
+	.log_start = mtty_log_start,
+	.log_stop = mtty_log_stop,
+	.log_read_and_clear = mtty_log_read_and_clear,
+};
+
 static int mtty_init_dev(struct vfio_device *vdev)
 {
 	struct mdev_state *mdev_state =
@@ -748,6 +1307,16 @@ static int mtty_init_dev(struct vfio_device *vdev)
 	mutex_init(&mdev_state->ops_lock);
 	mdev_state->mdev = mdev;
 	mtty_create_config_space(mdev_state);
+
+	mutex_init(&mdev_state->state_mutex);
+	mutex_init(&mdev_state->reset_mutex);
+	vdev->migration_flags = VFIO_MIGRATION_STOP_COPY |
+				VFIO_MIGRATION_P2P |
+				VFIO_MIGRATION_PRE_COPY;
+	vdev->mig_ops = &mtty_migration_ops;
+	vdev->log_ops = &mtty_log_ops;
+	mdev_state->state = VFIO_DEVICE_STATE_RUNNING;
+
 	return 0;
 
 err_nr_ports:
@@ -781,6 +1350,8 @@ static void mtty_release_dev(struct vfio_device *vdev)
 	struct mdev_state *mdev_state =
 		container_of(vdev, struct mdev_state, vdev);
 
+	mutex_destroy(&mdev_state->reset_mutex);
+	mutex_destroy(&mdev_state->state_mutex);
 	atomic_add(mdev_state->nr_ports, &mdev_avail_ports);
 	kfree(mdev_state->vconfig);
 }
@@ -797,6 +1368,15 @@ static int mtty_reset(struct mdev_state *mdev_state)
 {
 	pr_info("%s: called\n", __func__);
 
+	mutex_lock(&mdev_state->reset_mutex);
+	mdev_state->deferred_reset = true;
+	if (!mutex_trylock(&mdev_state->state_mutex)) {
+		mutex_unlock(&mdev_state->reset_mutex);
+		return 0;
+	}
+	mutex_unlock(&mdev_state->reset_mutex);
+	mtty_state_mutex_unlock(mdev_state);
+
 	return 0;
 }
 
@@ -1268,6 +1848,8 @@ static void mtty_close(struct vfio_device *vdev)
 	struct mdev_state *mdev_state =
 		container_of(vdev, struct mdev_state, vdev);
 
+	mtty_disable_files(mdev_state);
+
 	if (mdev_state->intx_evtfd) {
 		eventfd_ctx_put(mdev_state->intx_evtfd);
 		mdev_state->intx_evtfd = NULL;
-- 
2.40.1