[PATCH v10 Kernel 1/5] vfio: KABI for migration interface for device state

Kirti Wankhede
2019-12-16T20:50:38Z

- 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 added state transition details in the comment.

- Added sequence to be followed while saving and resuming VFIO device state

Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
Reviewed-by: Neo Jia <cjia@nvidia.com>
---
include/uapi/linux/vfio.h | 180 ++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 180 insertions(+)

diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 9e843a147ead..a0817ba267c1 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 +380,185 @@ 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)
+ * To indicate vendor driver the state VFIO device should be transitioned
+ * to. If device state transition fails, write on this field return error.
+ * It consists of 3 bits:
+ * - If bit 0 set, indicates _RUNNING state. When its 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 space 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. User should perform
+ * read-modify-write operation on this field.
+ *
+ * +------- _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 => Invalid 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
+ * |------------------------------------->|
+ *
+ * 2. Save state or Suspend
+ * |------------------------->|---------->|
+ *
+ * 3. Save state during live migration
+ * |----------->|------------>|---------->|
+ *
+ * 4. Resuming
+ * |<---------|
+ *
+ * 5. Resumed
+ * |--------->|
+ *
+ * 0. Default state of VFIO device is _RUNNNG when VFIO application starts.
+ * 1. During normal VFIO application shutdown, vfio device state changes
+ * from _RUNNING to _STOP.
+ * 2. When VFIO application save state or suspend application, VFIO device
+ * state transition is 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.
+ * On _RUNNING to stop-and-copy state transition failure, application should
+ * set VFIO device state to _RUNNING.
+ * 3. In VFIO application live migration, state transition is 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 application through migration
+ * region.
+ * On any failure during any of these state transition, VFIO device state
+ * should be set to _RUNNING.
+ * 4. To start resuming phase, VFIO 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.
+ * On failure during this state transition, application should set _RUNNING
+ * state.
+ * 5. On providing saved device data to driver, appliation should change state
+ * from _RESUMING to _RUNNING.
+ * On failure to transition to _RUNNING state, VFIO application should reset
+ * the device and set _RUNNING state so that device doesn't remain in unknown
+ * or bad state. On reset, driver must reset device and device should be
+ * available in default usable state.
+ *
+ * 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.
+ * If there was previous iteration, then this read operation indicates
+ * previous iteration is done. If pending_bytes > 0, go through below steps.
+ * b. read data_offset, indicates kernel driver to make data available through
+ * data section. Kernel 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.
+ * d. read data of data_size bytes from (region + data_offset) from migration
+ * region.
+ * e. process data.
+ * f. Loop through a to e.
+ *
+ * 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.
+ * c. write data_size which indicates vendor driver that data is written in
+ * staging buffer. Vendor driver should read this data from migration
+ * region and resume device's state.
+ *
+ * For user application, data is opaque. User should write data in the same
+ * order as received.
+ */
+
+struct vfio_device_migration_info {
+ __u32 device_state; /* VFIO device state */
+#define VFIO_DEVICE_STATE_STOP (1 << 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_INVALID_CASE1 (VFIO_DEVICE_STATE_SAVING | \
+ VFIO_DEVICE_STATE_RESUMING)
+
+#define VFIO_DEVICE_STATE_INVALID_CASE2 (VFIO_DEVICE_STATE_RUNNING | \
+ 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