[PATCH v12 Kernel 1/7] vfio: KABI for migration interface for device state

Kirti Wankhede
2020-02-07T20:16:27Z

- Defined MIGRATION region type and sub-type.

- Defined vfio_device_migration_info structure which will be placed at 0th
offset of migration region to get/set VFIO device related information.
Defined members of structure and usage on read/write access.

- Defined device states and state transition details.

- Defined sequence to be followed while saving and resuming VFIO device.

Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
Reviewed-by: Neo Jia <cjia@nvidia.com>
---
include/uapi/linux/vfio.h | 208 ++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 208 insertions(+)

diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 9e843a147ead..572242620ce9 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -305,6 +305,7 @@ struct vfio_region_info_cap_type {
#define VFIO_REGION_TYPE_PCI_VENDOR_MASK (0xffff)
#define VFIO_REGION_TYPE_GFX (1)
#define VFIO_REGION_TYPE_CCW (2)
+#define VFIO_REGION_TYPE_MIGRATION (3)

/* sub-types for VFIO_REGION_TYPE_PCI_* */

@@ -379,6 +380,213 @@ struct vfio_region_gfx_edid {
/* sub-types for VFIO_REGION_TYPE_CCW */
#define VFIO_REGION_SUBTYPE_CCW_ASYNC_CMD (1)

+/* sub-types for VFIO_REGION_TYPE_MIGRATION */
+#define VFIO_REGION_SUBTYPE_MIGRATION (1)
+
+/*
+ * Structure vfio_device_migration_info is placed at 0th offset of
+ * VFIO_REGION_SUBTYPE_MIGRATION region to get/set VFIO device related migration
+ * information. Field accesses from this structure are only supported at their
+ * native width and alignment, otherwise the result is undefined and vendor
+ * drivers should return an error.
+ *
+ * device_state: (read/write)
+ * - User application writes this field to inform vendor driver about the
+ * device state to be transitioned to.
+ * - Vendor driver should take necessary actions to change device state.
+ * On successful transition to given state, vendor driver should return
+ * success on write(device_state, state) system call. If device state
+ * transition fails, vendor driver should return error, -EFAULT.
+ * - On user application side, if device state transition fails, i.e. if
+ * write(device_state, state) returns error, read device_state again to
+ * determine the current state of the device from vendor driver.
+ * - Vendor driver should return previous state of the device unless vendor
+ * driver has encountered an internal error, in which case vendor driver
+ * may report the device_state VFIO_DEVICE_STATE_ERROR.
+ * - User application must use the device reset ioctl in order to recover
+ * the device from VFIO_DEVICE_STATE_ERROR state. If the device is
+ * indicated in a valid device state via reading device_state, the user
+ * application may decide attempt to transition the device to any valid
+ * state reachable from the current state or terminate itself.
+ *
+ * device_state consists of 3 bits:
+ * - If bit 0 set, indicates _RUNNING state. When it's clear, that
+ * indicates _STOP state. When device is changed to _STOP, driver should
+ * stop device before write() returns.
+ * - If bit 1 set, indicates _SAVING state. When set, that indicates driver
+ * should start gathering device state information which will be provided
+ * to VFIO user application to save device's state.
+ * - If bit 2 set, indicates _RESUMING state. When set, that indicates
+ * prepare to resume device, data provided through migration region
+ * should be used to resume device.
+ * Bits 3 - 31 are reserved for future use. In order to preserve them,
+ * user application should perform read-modify-write operation on this
+ * field when modifying the specified bits.
+ *
+ * +------- _RESUMING
+ * |+------ _SAVING
+ * ||+----- _RUNNING
+ * |||
+ * 000b => Device Stopped, not saving or resuming
+ * 001b => Device running state, default state
+ * 010b => Stop Device & save device state, stop-and-copy state
+ * 011b => Device running and save device state, pre-copy state
+ * 100b => Device stopped and device state is resuming
+ * 101b => Invalid state
+ * 110b => Error state
+ * 111b => Invalid state
+ *
+ * State transitions:
+ *
+ * _RESUMING _RUNNING Pre-copy Stop-and-copy _STOP
+ * (100b) (001b) (011b) (010b) (000b)
+ * 0. Running or Default state
+ * |
+ *
+ * 1. Normal Shutdown (optional)
+ * |------------------------------------->|
+ *
+ * 2. Save state or Suspend
+ * |------------------------->|---------->|
+ *
+ * 3. Save state during live migration
+ * |----------->|------------>|---------->|
+ *
+ * 4. Resuming
+ * |<---------|
+ *
+ * 5. Resumed
+ * |--------->|
+ *
+ * 0. Default state of VFIO device is _RUNNNG when user application starts.
+ * 1. During normal user application shutdown, vfio device state changes
+ * from _RUNNING to _STOP. This is optional, user application may or may not
+ * perform this state transition and vendor driver may not need.
+ * 2. When user application save state or suspend application, device state
+ * transitions from _RUNNING to stop-and-copy state and then to _STOP.
+ * On state transition from _RUNNING to stop-and-copy, driver must
+ * stop device, save device state and send it to application through
+ * migration region. Sequence to be followed for such transition is given
+ * below.
+ * 3. In user application live migration, state transitions from _RUNNING
+ * to pre-copy to stop-and-copy to _STOP.
+ * On state transition from _RUNNING to pre-copy, driver should start
+ * gathering device state while application is still running and send device
+ * state data to application through migration region.
+ * On state transition from pre-copy to stop-and-copy, driver must stop
+ * device, save device state and send it to user application through
+ * migration region.
+ * Sequence to be followed for above two transitions is given below.
+ * 4. To start resuming phase, device state should be transitioned from
+ * _RUNNING to _RESUMING state.
+ * In _RESUMING state, driver should use received device state data through
+ * migration region to resume device.
+ * 5. On providing saved device data to driver, application should change state
+ * from _RESUMING to _RUNNING.
+ *
+ * pending bytes: (read only)
+ * Number of pending bytes yet to be migrated from vendor driver
+ *
+ * data_offset: (read only)
+ * User application should read data_offset in migration region from where
+ * user application should read device data during _SAVING state or write
+ * device data during _RESUMING state. See below for detail of sequence to
+ * be followed.
+ *
+ * data_size: (read/write)
+ * User application should read data_size to get size of data copied in
+ * bytes in migration region during _SAVING state and write size of data
+ * copied in bytes in migration region during _RESUMING state.
+ *
+ * Migration region looks like:
+ * ------------------------------------------------------------------
+ * |vfio_device_migration_info| data section |
+ * | | /////////////////////////////// |
+ * ------------------------------------------------------------------
+ * ^ ^
+ * offset 0-trapped part data_offset
+ *
+ * Structure vfio_device_migration_info is always followed by data section in
+ * the region, so data_offset will always be non-0. Offset from where data is
+ * copied is decided by kernel driver, data section can be trapped or mapped
+ * or partitioned, depending on how kernel driver defines data section.
+ * Data section partition can be defined as mapped by sparse mmap capability.
+ * If mmapped, then data_offset should be page aligned, where as initial section
+ * which contain vfio_device_migration_info structure might not end at offset
+ * which is page aligned. The user is not required to access via mmap regardless
+ * of the region mmap capabilities.
+ * Vendor driver should decide whether to partition data section and how to
+ * partition the data section. Vendor driver should return data_offset
+ * accordingly.
+ *
+ * Sequence to be followed for _SAVING|_RUNNING device state or pre-copy phase
+ * and for _SAVING device state or stop-and-copy phase:
+ * a. read pending_bytes, indicates start of new iteration to get device data.
+ * Repeatative read on pending_bytes at this stage should have no side
+ * effect.
+ * If pending_bytes == 0, user application should not iterate to get data
+ * for that device.
+ * If pending_bytes > 0, go through below steps.
+ * b. read data_offset, indicates vendor driver to make data available through
+ * data section. Vendor driver should return this read operation only after
+ * data is available from (region + data_offset) to (region + data_offset +
+ * data_size).
+ * c. read data_size, amount of data in bytes available through migration
+ * region.
+ * Read on data_offset and data_size should return offset and size of current
+ * buffer if user application reads those more than once here.
+ * d. read data of data_size bytes from (region + data_offset) from migration
+ * region.
+ * e. process data.
+ * f. read pending_bytes, this read operation indicates data from previous
+ * iteration had read. If pending_bytes > 0, goto step b.
+ *
+ * If there is any error during the above sequence, vendor driver can return
+ * error code for next read()/write() operation, that will terminate the loop
+ * and user should take next necessary action, for example, fail migration or
+ * terminate user application.
+ *
+ * User application can transition from _SAVING|_RUNNING (pre-copy state) to
+ * _SAVING (stop-and-copy) state regardless of pending bytes.
+ * User application should iterate in _SAVING (stop-and-copy) until
+ * pending_bytes is 0.
+ *
+ * Sequence to be followed while _RESUMING device state:
+ * While data for this device is available, repeat below steps:
+ * a. read data_offset from where user application should write data.
+ * b. write data of data_size to migration region from data_offset. Data size
+ * should be data packet size at source during _SAVING.
+ * c. write data_size which indicates vendor driver that data is written in
+ * migration region. Vendor driver should read this data from migration
+ * region and resume device's state.
+ *
+ * For user application, data is opaque. User application should write data in
+ * the same order as received and should of same transaction size at source.
+ */
+
+struct vfio_device_migration_info {
+ __u32 device_state; /* VFIO device state */
+#define VFIO_DEVICE_STATE_STOP (0)
+#define VFIO_DEVICE_STATE_RUNNING (1 << 0)
+#define VFIO_DEVICE_STATE_SAVING (1 << 1)
+#define VFIO_DEVICE_STATE_RESUMING (1 << 2)
+#define VFIO_DEVICE_STATE_MASK (VFIO_DEVICE_STATE_RUNNING | \
+ VFIO_DEVICE_STATE_SAVING | \
+ VFIO_DEVICE_STATE_RESUMING)
+
+#define VFIO_DEVICE_STATE_VALID(state) \
+ (state & VFIO_DEVICE_STATE_RESUMING ? \
+ (state & VFIO_DEVICE_STATE_MASK) == VFIO_DEVICE_STATE_RESUMING : 1)
+
+#define VFIO_DEVICE_STATE_ERROR \
+ (VFIO_DEVICE_STATE_SAVING | VFIO_DEVICE_STATE_RESUMING)
+
+ __u32 reserved;
+ __u64 pending_bytes;
+ __u64 data_offset;
+ __u64 data_size;
+} __attribute__((packed));
+
/*
* The MSIX mappable capability informs that MSIX data of a BAR can be mmapped
* which allows direct access to non-MSIX registers which happened to be within
--
2.7.0