Re: [PATCH v7 05/15] s390/vfio-ap: Callback to get/set vfio device mig state during guest migration
From: Anthony Krowiak
Date: Mon Oct 05 2026 - 16:43:01 EST
On 8/12/26 12:04 PM, Jason J. Herne wrote:
On 8/7/26 6:18 PM, Anthony Krowiak wrote:
Implements two callbacks related to the current state of a vfio-ap device:
* The callback that sets a new migration state of a vfio-ap device during
live migration of guests with pass-through access to AP devices. This
callback is mandatory for VFIO_DEVICE_FEATURE_MIGRATION support.
The function pointer for this callback is specified via the
'migration_set_state' field of the 'vfio_migration_ops' structure
which is stored with the VFIO device when the 'vfio_device'
structure representing the mediated device is initialized.
* The callback that returns the current vfio device migration state during
live migration of guests with pass-through access to AP devices.
The function pointer for this callback is specified via the
'migration_get_state' field of the 'vfio_migration_ops' structure
which is stored with the VFIO device when the 'vfio_device'
structure representing the mediated device is initialized.
Signed-off-by: Anthony Krowiak <akrowiak@xxxxxxxxxxxxx>
---
drivers/s390/crypto/vfio_ap_migration.c | 130 +++++++++++++++++++++++-
1 file changed, 128 insertions(+), 2 deletions(-)
diff --git a/drivers/s390/crypto/vfio_ap_migration.c b/drivers/s390/crypto/vfio_ap_migration.c
index 1613813124b6..af740b177c97 100644
--- a/drivers/s390/crypto/vfio_ap_migration.c
+++ b/drivers/s390/crypto/vfio_ap_migration.c
@@ -128,16 +128,141 @@ static void vfio_ap_release_resuming_file(struct vfio_ap_migration_data *mig_dat
*/
}
+static struct file *
+vfio_ap_transition_to_state(struct ap_matrix_mdev *matrix_mdev,
+ enum vfio_device_mig_state new_state)
+{
+ struct vfio_ap_migration_data *mig_data;
+ enum vfio_device_mig_state cur_state;
+
+ lockdep_assert_held(&matrix_dev->mdevs_lock);
+ mig_data = matrix_mdev->mig_data;
+ cur_state = mig_data->mig_state;
+ dev_dbg(matrix_mdev->vdev.dev, "%s: %d -> %d\n", __func__, cur_state,
+ new_state);
+
+ if (cur_state == VFIO_DEVICE_STATE_STOP &&
+ new_state == VFIO_DEVICE_STATE_STOP_COPY) {
+ /* TODO */
+ return ERR_PTR(-EOPNOTSUPP);
+ }
+
+ if (cur_state == VFIO_DEVICE_STATE_STOP &&
+ new_state == VFIO_DEVICE_STATE_RESUMING) {
+ /* TODO */
+ return ERR_PTR(-EOPNOTSUPP);
+ }
+
+ if ((cur_state == VFIO_DEVICE_STATE_RESUMING &&
+ new_state == VFIO_DEVICE_STATE_STOP) ||
+ (cur_state == VFIO_DEVICE_STATE_STOP_COPY &&
+ new_state == VFIO_DEVICE_STATE_STOP)) {
+ /* TODO */
+ return ERR_PTR(-EOPNOTSUPP);
+ }
+
+ if ((cur_state == VFIO_DEVICE_STATE_STOP &&
+ new_state == VFIO_DEVICE_STATE_RUNNING) ||
+ (cur_state == VFIO_DEVICE_STATE_RUNNING &&
+ new_state == VFIO_DEVICE_STATE_STOP)) {
+ /* TODO */
+ return ERR_PTR(-EOPNOTSUPP);
+ }
+
+ /* vfio_mig_get_next_state() does not use arcs other than the above */
+ WARN_ON(true);
+
+ return ERR_PTR(-EINVAL);
+}
+
static struct file *vfio_ap_set_state(struct vfio_device *vdev,
enum vfio_device_mig_state new_state)
{
- return NULL;
+ int ret;
+ struct file *filp = NULL;
+ struct ap_matrix_mdev *matrix_mdev;
+ enum vfio_device_mig_state next_state;
+ struct vfio_ap_migration_data *mig_data;
+
+ matrix_mdev = container_of(vdev, struct ap_matrix_mdev, vdev);
The container_of() pointer swizzle is done under lock in vfio_ap_get_state, but not here. Why? They should probably be handled consistently.
The vdev pointer is stable. It is passed in as a function parameter from the
VFIO core and is guaranteed valid for the callback duration. On the other
hand, in the interest of consistency - as you explained - I'll move it after
taking the mdevs_lock.
+
+ mutex_lock(&matrix_dev->mdevs_lock);
+ if (ap_is_se_guest()) {
+ dev_err_once(matrix_mdev->vdev.dev,
+ "Migration not allowed from or to a Secure Execution guest\n");
+ mutex_unlock(&matrix_dev->mdevs_lock);
+ return ERR_PTR(-EPERM);
+ }
+
+ mig_data = matrix_mdev->mig_data;
+
+ /*
+ * The mig_data pointer is set in the vfio_ap_init_migration_data
+ * function which is called when the vfio-ap device fd is opened.
+ * Since the implicit pre-open state is RUNNING, a request to set
+ * RUNNING is a no-op. Any other state transition is invalid before
+ * open_device.
+ */
+ if (!mig_data) {
+ mutex_unlock(&matrix_dev->mdevs_lock);
+ if (new_state == VFIO_DEVICE_STATE_RUNNING)
+ return NULL;
+ return ERR_PTR(-ENODEV);
+ }
+
+ dev_dbg(vdev->dev, "%s -> %d\n", __func__, new_state);
+
+ while (mig_data->mig_state != VFIO_DEVICE_STATE_ERROR &&
+ mig_data->mig_state != new_state) {
+ ret = vfio_mig_get_next_state(vdev, mig_data->mig_state,
+ new_state, &next_state);
+ if (ret) {
+ filp = ERR_PTR(ret);
+ break;
+ }
+
+ filp = vfio_ap_transition_to_state(matrix_mdev, next_state);
+ if (IS_ERR(filp))
+ break;
+
+ mig_data->mig_state = next_state;
+
+ if (WARN_ON(filp && new_state != next_state)) {
+ fput(filp);
+ filp = ERR_PTR(-EINVAL);
+ break;
+ }
+ }
+
+ mutex_unlock(&matrix_dev->mdevs_lock);
+
+ return filp;
}
static int vfio_ap_get_state(struct vfio_device *vdev,
enum vfio_device_mig_state *current_state)
{
- return -EOPNOTSUPP;
+ struct ap_matrix_mdev *matrix_mdev;
+ struct vfio_ap_migration_data *mig_data;
+
+ mutex_lock(&matrix_dev->mdevs_lock);
+
+ matrix_mdev = container_of(vdev, struct ap_matrix_mdev, vdev);
+ mig_data = matrix_mdev->mig_data;
Why bother with temp variable? You could just access matrix_mdev->mig_data directly.
No other reason than for readability and shortening lines of code that access it multiple
times. I see no good reason to remove it.
+
+ /*
+ * The mig_data pointer is set in the vfio_ap_init_migration_data
+ * function which is called when the vfio-ap device fd is opened.
+ * If mig_data is NULL, report RUNNING as the implicit pre-open state
+ * so userspace doesn't need to perform any state transition before the
+ * device becomes active.
+ */
+ *current_state = (mig_data) ? mig_data->mig_state :
+ VFIO_DEVICE_STATE_RUNNING;
+
+ mutex_unlock(&matrix_dev->mdevs_lock);
+
+ return 0;
}
static int vfio_ap_get_data_size(struct vfio_device *vdev,
@@ -159,6 +284,7 @@ static const struct vfio_migration_ops vfio_ap_migration_ops = {
*/
void vfio_ap_init_migration_capabilities(struct ap_matrix_mdev *matrix_mdev)
{
+ /* Live guest migration is not supported for SE guests */
if (ap_is_se_guest())
return;
Comment is unrelated to the rest of the patch.
This belongs in patch 03/15. I'll move it.