Re: [PATCH v7 02/15] s390/vfio-ap: Data structures for facilitating vfio device migration

[Jason J. Herne]

On 8/7/26 6:18 PM, Anthony Krowiak wrote:
> Creates the data structures used to facilitate state transitions during
> vfio device migration.
>
> Signed-off-by: Anthony Krowiak <akrowiak@xxxxxxxxxxxxx>
> ---
>   drivers/s390/crypto/Makefile            |   2 +-
>   drivers/s390/crypto/vfio_ap_migration.c | 113 ++++++++++++++++++++++++
>   drivers/s390/crypto/vfio_ap_private.h   |   5 ++
>   3 files changed, 119 insertions(+), 1 deletion(-)
>   create mode 100644 drivers/s390/crypto/vfio_ap_migration.c
>
> diff --git a/drivers/s390/crypto/Makefile b/drivers/s390/crypto/Makefile
> index e83c6603c858..20f29184825a 100644
> --- a/drivers/s390/crypto/Makefile
> +++ b/drivers/s390/crypto/Makefile
> @@ -34,5 +34,5 @@ pkey-uv-objs := pkey_uv.o
>   obj-$(CONFIG_PKEY_UV) += pkey-uv.o
>   
>   # adjunct processor matrix
> -vfio_ap-objs := vfio_ap_drv.o vfio_ap_ops.o
> +vfio_ap-objs := vfio_ap_drv.o vfio_ap_ops.o vfio_ap_migration.o
>   obj-$(CONFIG_VFIO_AP) += vfio_ap.o
> diff --git a/drivers/s390/crypto/vfio_ap_migration.c b/drivers/s390/crypto/vfio_ap_migration.c
> new file mode 100644
> index 000000000000..374d3a67cb21
> --- /dev/null
> +++ b/drivers/s390/crypto/vfio_ap_migration.c
> @@ -0,0 +1,113 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Drives vfio_ap mdev migration.
> + *
> + * Copyright IBM Corp. 2025
> + */
> +#include "vfio_ap_private.h"
> +
> +/* Magic number and version for the vfio_ap_config migration blob */
> +#define VFIO_AP_MIG_MAGIC			0x76666170U  /* "vfap" */
> +#define VFIO_AP_MIG_VERSION			1U
> +
> +/**
> + * struct vfio_ap_migration_file
> + *
> + * This object is used for chunk processing of multiple reads and writes of
> + * AP configuration information.
> + *
> + * @filp:	file stream used to read or write AP configuration data
> + * @ap_config:	object used to store AP configuration data between read or write
> + *		calls
> + * @config_sz:	the size (in bytes) of @ap_config
> + */
> +struct vfio_ap_migration_file {
> +	struct file		*filp;
> +	struct vfio_ap_config	*ap_config;
> +	unsigned long		config_sz;
> +};
> +
> +/**
> + * struct vfio_ap_migration_data:
> + *
> + * Manages the migration state for the VFIO device that maintains the AP
> + * configuration of the guest being migrated.
> + *
> + * @mig_state:		the current migration state
> + * @resuming_mig_file:	the object used to restore the state of the vfio-ap
> + *			device on the destination host.
> + * @stop_copy_mig_file:	the object used to store the AP configuration of the
> + *			source guest for transfer to the destination host.
> + */
> +struct vfio_ap_migration_data {
> +	enum vfio_device_mig_state	mig_state;
> +	struct vfio_ap_migration_file	resuming_mig_file;
> +	struct vfio_ap_migration_file	stop_copy_mig_file;
> +};
> +
> +/**
> + * struct vfio_ap_queue_info - the information for an AP queue
> + *
> + * @data: contains the queue information returned in GR2 from the PQAP(TAPQ)
> + *	  command
> + * @apqn: the APQN of the queue
> + * @reserved: padding to ensure consistent structure size across platforms
> + */
> +struct vfio_ap_queue_info {
> +	u64 data;
> +	u16 apqn;
> +	u8  reserved[6];
> +};
> +
> +/**
> + * struct vfio_ap_config:
> + *
> + * Stores the state of a guest's AP configuration.
> + *
> + * VFIO device migration state transition from STOP to STOP_COPY:
> + * -------------------------------------------------------------
> + * When the migration state transitions from STOP to STOP_COPY, the vfio_ap device
> + * driver will open a file stream in read-only mode and return the fd to userspace.
> + * This fd is used during the STOP_COPY phase to read the current state of the
> + * vfio-ap device on the source host. In response, the driver will store the
> + * source guest's AP configuration data in a vfio_ap_config object and copy it to
> + * userspace.
> + *
> + * VFIO device migration state transition from STOP to RESUMING:
> + * ------------------------------------------------------------
> + * When the VFIO migration state transitions from STOP to RESUMING,
> + * the vfio_ap device driver will open a file stream in write-only mode and
> + * return the fd to userspace. This fd is used during the RESUMING phase to
> + * write the source guest's vfio_ap_config data that was read in during the
> + * STOP_COPY phase to the vfio_ap device driver on the destination host. In
> + * response, the device driver will copy the data sent from userspace to a
> + * vfio_ap_config instance which is then used to update the destination guest's
> + * AP configuration.
> + *
> + * Since the source and destination hosts may be running different versions of
> + * the linux kernel, the vfio_ap_config object provides two fields (@magic and
> + * @version) which must be set by the source device driver and verified by the
> + * destination device driver to ensure the migration ABI of the source and
> + * destination hosts are compatible.
> + *
> + * Note: Since a guest's AP configuration could be comprise of a large number of

Typo. I think you wanted 'comprised' here.

Reviewed-by: Jason J. Herne <jjherne@xxxxxxxxxxxxx>