lkml.org 
[lkml]   [2023]   [Oct]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH 2/2] vfio/mtty: Enable migration support
From
On 10/13/23 21:56, Alex Williamson wrote:
> 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@redhat.com>
> ---
>
> Much of this should look familiar to vfio-pci variant driver developers
> ;)


LGTM, though, I would isolate the part doing the get/set of the device
state in their own routine to avoid extra noise in mtty_save_device_data()
and mtty_resume_write(). The size of the state could also be dynamic and
computed like done in .migration_get_data_size() handler. This is only
a sample, so it might be worth the extra effort.

That said, this driver could be a summary of the best practice to follow
when implementing support for VFIO migration.

Thanks,

C.

>
> 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;

\
 
 \ /
  Last update: 2023-10-16 16:31    [W:0.074 / U:0.056 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site