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Mon, 5 Dec 2022 06:49:11 -0800 Received: from rnnvmail205.nvidia.com (10.129.68.10) by rnnvmail205.nvidia.com (10.129.68.10) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.986.36; Mon, 5 Dec 2022 06:49:10 -0800 Received: from vdi.nvidia.com (10.127.8.10) by mail.nvidia.com (10.129.68.10) with Microsoft SMTP Server id 15.2.986.36 via Frontend Transport; Mon, 5 Dec 2022 06:49:07 -0800 From: Yishai Hadas To: , CC: , , , , , , , , , Subject: [PATCH V3 vfio 02/14] vfio: Extend the device migration protocol with PRE_COPY Date: Mon, 5 Dec 2022 16:48:26 +0200 Message-ID: <20221205144838.245287-3-yishaih@nvidia.com> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20221205144838.245287-1-yishaih@nvidia.com> References: <20221205144838.245287-1-yishaih@nvidia.com> MIME-Version: 1.0 X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CO1NAM11FT017:EE_|CH0PR12MB5265:EE_ X-MS-Office365-Filtering-Correlation-Id: d930197f-f187-416c-84b7-08dad6cfe3df X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 05 Dec 2022 14:49:19.5059 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: d930197f-f187-416c-84b7-08dad6cfe3df X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.160];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CO1NAM11FT017.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH0PR12MB5265 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org From: Jason Gunthorpe The optional PRE_COPY states open the saving data transfer FD before reaching STOP_COPY and allows the device to dirty track internal state changes with the general idea to reduce the volume of data transferred in the STOP_COPY stage. While in PRE_COPY the device remains RUNNING, but the saving FD is open. Only if the device also supports RUNNING_P2P can it support PRE_COPY_P2P, which halts P2P transfers while continuing the saving FD. PRE_COPY, with P2P support, requires the driver to implement 7 new arcs and exists as an optional FSM branch between RUNNING and STOP_COPY: RUNNING -> PRE_COPY -> PRE_COPY_P2P -> STOP_COPY A new ioctl VFIO_MIG_GET_PRECOPY_INFO is provided to allow userspace to query the progress of the precopy operation in the driver with the idea it will judge to move to STOP_COPY at least once the initial data set is transferred, and possibly after the dirty size has shrunk appropriately. This ioctl is valid only in PRE_COPY states and kernel driver should return -EINVAL from any other migration state. Compared to the v1 clarification, STOP_COPY -> PRE_COPY is blocked and to be defined in future. We also split the pending_bytes report into the initial and sustaining values, e.g.: initial_bytes and dirty_bytes. initial_bytes: Amount of initial precopy data. dirty_bytes: Device state changes relative to data previously retrieved. These fields are not required to have any bearing to STOP_COPY phase. It is recommended to leave PRE_COPY for STOP_COPY only after the initial_bytes field reaches zero. Leaving PRE_COPY earlier might make things slower. Signed-off-by: Jason Gunthorpe Signed-off-by: Shay Drory Reviewed-by: Kevin Tian Reviewed-by: Shameer Kolothum Signed-off-by: Yishai Hadas --- drivers/vfio/vfio_main.c | 74 ++++++++++++++++++++++- include/uapi/linux/vfio.h | 123 ++++++++++++++++++++++++++++++++++++-- 2 files changed, 191 insertions(+), 6 deletions(-) diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c index 662e267a3e13..9c4a752dad4e 100644 --- a/drivers/vfio/vfio_main.c +++ b/drivers/vfio/vfio_main.c @@ -1042,7 +1042,7 @@ int vfio_mig_get_next_state(struct vfio_device *device, enum vfio_device_mig_state new_fsm, enum vfio_device_mig_state *next_fsm) { - enum { VFIO_DEVICE_NUM_STATES = VFIO_DEVICE_STATE_RUNNING_P2P + 1 }; + enum { VFIO_DEVICE_NUM_STATES = VFIO_DEVICE_STATE_PRE_COPY_P2P + 1 }; /* * The coding in this table requires the driver to implement the * following FSM arcs: @@ -1057,30 +1057,65 @@ int vfio_mig_get_next_state(struct vfio_device *device, * RUNNING_P2P -> RUNNING * RUNNING_P2P -> STOP * STOP -> RUNNING_P2P - * Without P2P the driver must implement: + * + * If precopy is supported then the driver must support these additional + * FSM arcs: + * RUNNING -> PRE_COPY + * PRE_COPY -> RUNNING + * PRE_COPY -> STOP_COPY + * However, if precopy and P2P are supported together then the driver + * must support these additional arcs beyond the P2P arcs above: + * PRE_COPY -> RUNNING + * PRE_COPY -> PRE_COPY_P2P + * PRE_COPY_P2P -> PRE_COPY + * PRE_COPY_P2P -> RUNNING_P2P + * PRE_COPY_P2P -> STOP_COPY + * RUNNING -> PRE_COPY + * RUNNING_P2P -> PRE_COPY_P2P + * + * Without P2P and precopy the driver must implement: * RUNNING -> STOP * STOP -> RUNNING * * The coding will step through multiple states for some combination * transitions; if all optional features are supported, this means the * following ones: + * PRE_COPY -> PRE_COPY_P2P -> STOP_COPY + * PRE_COPY -> RUNNING -> RUNNING_P2P + * PRE_COPY -> RUNNING -> RUNNING_P2P -> STOP + * PRE_COPY -> RUNNING -> RUNNING_P2P -> STOP -> RESUMING + * PRE_COPY_P2P -> RUNNING_P2P -> RUNNING + * PRE_COPY_P2P -> RUNNING_P2P -> STOP + * PRE_COPY_P2P -> RUNNING_P2P -> STOP -> RESUMING * RESUMING -> STOP -> RUNNING_P2P + * RESUMING -> STOP -> RUNNING_P2P -> PRE_COPY_P2P * RESUMING -> STOP -> RUNNING_P2P -> RUNNING + * RESUMING -> STOP -> RUNNING_P2P -> RUNNING -> PRE_COPY * RESUMING -> STOP -> STOP_COPY + * RUNNING -> RUNNING_P2P -> PRE_COPY_P2P * RUNNING -> RUNNING_P2P -> STOP * RUNNING -> RUNNING_P2P -> STOP -> RESUMING * RUNNING -> RUNNING_P2P -> STOP -> STOP_COPY + * RUNNING_P2P -> RUNNING -> PRE_COPY * RUNNING_P2P -> STOP -> RESUMING * RUNNING_P2P -> STOP -> STOP_COPY + * STOP -> RUNNING_P2P -> PRE_COPY_P2P * STOP -> RUNNING_P2P -> RUNNING + * STOP -> RUNNING_P2P -> RUNNING -> PRE_COPY * STOP_COPY -> STOP -> RESUMING * STOP_COPY -> STOP -> RUNNING_P2P * STOP_COPY -> STOP -> RUNNING_P2P -> RUNNING + * + * The following transitions are blocked: + * STOP_COPY -> PRE_COPY + * STOP_COPY -> PRE_COPY_P2P */ static const u8 vfio_from_fsm_table[VFIO_DEVICE_NUM_STATES][VFIO_DEVICE_NUM_STATES] = { [VFIO_DEVICE_STATE_STOP] = { [VFIO_DEVICE_STATE_STOP] = VFIO_DEVICE_STATE_STOP, [VFIO_DEVICE_STATE_RUNNING] = VFIO_DEVICE_STATE_RUNNING_P2P, + [VFIO_DEVICE_STATE_PRE_COPY] = VFIO_DEVICE_STATE_RUNNING_P2P, + [VFIO_DEVICE_STATE_PRE_COPY_P2P] = VFIO_DEVICE_STATE_RUNNING_P2P, [VFIO_DEVICE_STATE_STOP_COPY] = VFIO_DEVICE_STATE_STOP_COPY, [VFIO_DEVICE_STATE_RESUMING] = VFIO_DEVICE_STATE_RESUMING, [VFIO_DEVICE_STATE_RUNNING_P2P] = VFIO_DEVICE_STATE_RUNNING_P2P, @@ -1089,14 +1124,38 @@ int vfio_mig_get_next_state(struct vfio_device *device, [VFIO_DEVICE_STATE_RUNNING] = { [VFIO_DEVICE_STATE_STOP] = VFIO_DEVICE_STATE_RUNNING_P2P, [VFIO_DEVICE_STATE_RUNNING] = VFIO_DEVICE_STATE_RUNNING, + [VFIO_DEVICE_STATE_PRE_COPY] = VFIO_DEVICE_STATE_PRE_COPY, + [VFIO_DEVICE_STATE_PRE_COPY_P2P] = VFIO_DEVICE_STATE_RUNNING_P2P, [VFIO_DEVICE_STATE_STOP_COPY] = VFIO_DEVICE_STATE_RUNNING_P2P, [VFIO_DEVICE_STATE_RESUMING] = VFIO_DEVICE_STATE_RUNNING_P2P, [VFIO_DEVICE_STATE_RUNNING_P2P] = VFIO_DEVICE_STATE_RUNNING_P2P, [VFIO_DEVICE_STATE_ERROR] = VFIO_DEVICE_STATE_ERROR, }, + [VFIO_DEVICE_STATE_PRE_COPY] = { + [VFIO_DEVICE_STATE_STOP] = VFIO_DEVICE_STATE_RUNNING, + [VFIO_DEVICE_STATE_RUNNING] = VFIO_DEVICE_STATE_RUNNING, + [VFIO_DEVICE_STATE_PRE_COPY] = VFIO_DEVICE_STATE_PRE_COPY, + [VFIO_DEVICE_STATE_PRE_COPY_P2P] = VFIO_DEVICE_STATE_PRE_COPY_P2P, + [VFIO_DEVICE_STATE_STOP_COPY] = VFIO_DEVICE_STATE_PRE_COPY_P2P, + [VFIO_DEVICE_STATE_RESUMING] = VFIO_DEVICE_STATE_RUNNING, + [VFIO_DEVICE_STATE_RUNNING_P2P] = VFIO_DEVICE_STATE_RUNNING, + [VFIO_DEVICE_STATE_ERROR] = VFIO_DEVICE_STATE_ERROR, + }, + [VFIO_DEVICE_STATE_PRE_COPY_P2P] = { + [VFIO_DEVICE_STATE_STOP] = VFIO_DEVICE_STATE_RUNNING_P2P, + [VFIO_DEVICE_STATE_RUNNING] = VFIO_DEVICE_STATE_RUNNING_P2P, + [VFIO_DEVICE_STATE_PRE_COPY] = VFIO_DEVICE_STATE_PRE_COPY, + [VFIO_DEVICE_STATE_PRE_COPY_P2P] = VFIO_DEVICE_STATE_PRE_COPY_P2P, + [VFIO_DEVICE_STATE_STOP_COPY] = VFIO_DEVICE_STATE_STOP_COPY, + [VFIO_DEVICE_STATE_RESUMING] = VFIO_DEVICE_STATE_RUNNING_P2P, + [VFIO_DEVICE_STATE_RUNNING_P2P] = VFIO_DEVICE_STATE_RUNNING_P2P, + [VFIO_DEVICE_STATE_ERROR] = VFIO_DEVICE_STATE_ERROR, + }, [VFIO_DEVICE_STATE_STOP_COPY] = { [VFIO_DEVICE_STATE_STOP] = VFIO_DEVICE_STATE_STOP, [VFIO_DEVICE_STATE_RUNNING] = VFIO_DEVICE_STATE_STOP, + [VFIO_DEVICE_STATE_PRE_COPY] = VFIO_DEVICE_STATE_ERROR, + [VFIO_DEVICE_STATE_PRE_COPY_P2P] = VFIO_DEVICE_STATE_ERROR, [VFIO_DEVICE_STATE_STOP_COPY] = VFIO_DEVICE_STATE_STOP_COPY, [VFIO_DEVICE_STATE_RESUMING] = VFIO_DEVICE_STATE_STOP, [VFIO_DEVICE_STATE_RUNNING_P2P] = VFIO_DEVICE_STATE_STOP, @@ -1105,6 +1164,8 @@ int vfio_mig_get_next_state(struct vfio_device *device, [VFIO_DEVICE_STATE_RESUMING] = { [VFIO_DEVICE_STATE_STOP] = VFIO_DEVICE_STATE_STOP, [VFIO_DEVICE_STATE_RUNNING] = VFIO_DEVICE_STATE_STOP, + [VFIO_DEVICE_STATE_PRE_COPY] = VFIO_DEVICE_STATE_STOP, + [VFIO_DEVICE_STATE_PRE_COPY_P2P] = VFIO_DEVICE_STATE_STOP, [VFIO_DEVICE_STATE_STOP_COPY] = VFIO_DEVICE_STATE_STOP, [VFIO_DEVICE_STATE_RESUMING] = VFIO_DEVICE_STATE_RESUMING, [VFIO_DEVICE_STATE_RUNNING_P2P] = VFIO_DEVICE_STATE_STOP, @@ -1113,6 +1174,8 @@ int vfio_mig_get_next_state(struct vfio_device *device, [VFIO_DEVICE_STATE_RUNNING_P2P] = { [VFIO_DEVICE_STATE_STOP] = VFIO_DEVICE_STATE_STOP, [VFIO_DEVICE_STATE_RUNNING] = VFIO_DEVICE_STATE_RUNNING, + [VFIO_DEVICE_STATE_PRE_COPY] = VFIO_DEVICE_STATE_RUNNING, + [VFIO_DEVICE_STATE_PRE_COPY_P2P] = VFIO_DEVICE_STATE_PRE_COPY_P2P, [VFIO_DEVICE_STATE_STOP_COPY] = VFIO_DEVICE_STATE_STOP, [VFIO_DEVICE_STATE_RESUMING] = VFIO_DEVICE_STATE_STOP, [VFIO_DEVICE_STATE_RUNNING_P2P] = VFIO_DEVICE_STATE_RUNNING_P2P, @@ -1121,6 +1184,8 @@ int vfio_mig_get_next_state(struct vfio_device *device, [VFIO_DEVICE_STATE_ERROR] = { [VFIO_DEVICE_STATE_STOP] = VFIO_DEVICE_STATE_ERROR, [VFIO_DEVICE_STATE_RUNNING] = VFIO_DEVICE_STATE_ERROR, + [VFIO_DEVICE_STATE_PRE_COPY] = VFIO_DEVICE_STATE_ERROR, + [VFIO_DEVICE_STATE_PRE_COPY_P2P] = VFIO_DEVICE_STATE_ERROR, [VFIO_DEVICE_STATE_STOP_COPY] = VFIO_DEVICE_STATE_ERROR, [VFIO_DEVICE_STATE_RESUMING] = VFIO_DEVICE_STATE_ERROR, [VFIO_DEVICE_STATE_RUNNING_P2P] = VFIO_DEVICE_STATE_ERROR, @@ -1131,6 +1196,11 @@ int vfio_mig_get_next_state(struct vfio_device *device, static const unsigned int state_flags_table[VFIO_DEVICE_NUM_STATES] = { [VFIO_DEVICE_STATE_STOP] = VFIO_MIGRATION_STOP_COPY, [VFIO_DEVICE_STATE_RUNNING] = VFIO_MIGRATION_STOP_COPY, + [VFIO_DEVICE_STATE_PRE_COPY] = + VFIO_MIGRATION_STOP_COPY | VFIO_MIGRATION_PRE_COPY, + [VFIO_DEVICE_STATE_PRE_COPY_P2P] = VFIO_MIGRATION_STOP_COPY | + VFIO_MIGRATION_P2P | + VFIO_MIGRATION_PRE_COPY, [VFIO_DEVICE_STATE_STOP_COPY] = VFIO_MIGRATION_STOP_COPY, [VFIO_DEVICE_STATE_RESUMING] = VFIO_MIGRATION_STOP_COPY, [VFIO_DEVICE_STATE_RUNNING_P2P] = diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h index 3e45dbaf190e..23105eb036fa 100644 --- a/include/uapi/linux/vfio.h +++ b/include/uapi/linux/vfio.h @@ -819,12 +819,20 @@ struct vfio_device_feature { * VFIO_MIGRATION_STOP_COPY | VFIO_MIGRATION_P2P means that RUNNING_P2P * is supported in addition to the STOP_COPY states. * + * VFIO_MIGRATION_STOP_COPY | VFIO_MIGRATION_PRE_COPY means that + * PRE_COPY is supported in addition to the STOP_COPY states. + * + * VFIO_MIGRATION_STOP_COPY | VFIO_MIGRATION_P2P | VFIO_MIGRATION_PRE_COPY + * means that RUNNING_P2P, PRE_COPY and PRE_COPY_P2P are supported + * in addition to the STOP_COPY states. + * * Other combinations of flags have behavior to be defined in the future. */ struct vfio_device_feature_migration { __aligned_u64 flags; #define VFIO_MIGRATION_STOP_COPY (1 << 0) #define VFIO_MIGRATION_P2P (1 << 1) +#define VFIO_MIGRATION_PRE_COPY (1 << 2) }; #define VFIO_DEVICE_FEATURE_MIGRATION 1 @@ -875,8 +883,13 @@ struct vfio_device_feature_mig_state { * RESUMING - The device is stopped and is loading a new internal state * ERROR - The device has failed and must be reset * - * And 1 optional state to support VFIO_MIGRATION_P2P: + * And optional states to support VFIO_MIGRATION_P2P: * RUNNING_P2P - RUNNING, except the device cannot do peer to peer DMA + * And VFIO_MIGRATION_PRE_COPY: + * PRE_COPY - The device is running normally but tracking internal state + * changes + * And VFIO_MIGRATION_P2P | VFIO_MIGRATION_PRE_COPY: + * PRE_COPY_P2P - PRE_COPY, except the device cannot do peer to peer DMA * * The FSM takes actions on the arcs between FSM states. The driver implements * the following behavior for the FSM arcs: @@ -908,20 +921,48 @@ struct vfio_device_feature_mig_state { * * To abort a RESUMING session the device must be reset. * + * PRE_COPY -> RUNNING * RUNNING_P2P -> RUNNING * While in RUNNING the device is fully operational, the device may generate * interrupts, DMA, respond to MMIO, all vfio device regions are functional, * and the device may advance its internal state. * + * The PRE_COPY arc will terminate a data transfer session. + * + * PRE_COPY_P2P -> RUNNING_P2P * RUNNING -> RUNNING_P2P * STOP -> RUNNING_P2P * While in RUNNING_P2P the device is partially running in the P2P quiescent * state defined below. * + * The PRE_COPY_P2P arc will terminate a data transfer session. + * + * RUNNING -> PRE_COPY + * RUNNING_P2P -> PRE_COPY_P2P * STOP -> STOP_COPY - * This arc begin the process of saving the device state and will return a - * new data_fd. + * PRE_COPY, PRE_COPY_P2P and STOP_COPY form the "saving group" of states + * which share a data transfer session. Moving between these states alters + * what is streamed in session, but does not terminate or otherwise affect + * the associated fd. + * + * These arcs begin the process of saving the device state and will return a + * new data_fd. The migration driver may perform actions such as enabling + * dirty logging of device state when entering PRE_COPY or PER_COPY_P2P. * + * Each arc does not change the device operation, the device remains + * RUNNING, P2P quiesced or in STOP. The STOP_COPY state is described below + * in PRE_COPY_P2P -> STOP_COPY. + * + * PRE_COPY -> PRE_COPY_P2P + * Entering PRE_COPY_P2P continues all the behaviors of PRE_COPY above. + * However, while in the PRE_COPY_P2P state, the device is partially running + * in the P2P quiescent state defined below, like RUNNING_P2P. + * + * PRE_COPY_P2P -> PRE_COPY + * This arc allows returning the device to a full RUNNING behavior while + * continuing all the behaviors of PRE_COPY. + * + * PRE_COPY_P2P -> STOP_COPY * While in the STOP_COPY state the device has the same behavior as STOP * with the addition that the data transfers session continues to stream the * migration state. End of stream on the FD indicates the entire device @@ -939,6 +980,13 @@ struct vfio_device_feature_mig_state { * device state for this arc if required to prepare the device to receive the * migration data. * + * STOP_COPY -> PRE_COPY + * STOP_COPY -> PRE_COPY_P2P + * These arcs are not permitted and return error if requested. Future + * revisions of this API may define behaviors for these arcs, in this case + * support will be discoverable by a new flag in + * VFIO_DEVICE_FEATURE_MIGRATION. + * * any -> ERROR * ERROR cannot be specified as a device state, however any transition request * can be failed with an errno return and may then move the device_state into @@ -950,7 +998,7 @@ struct vfio_device_feature_mig_state { * The optional peer to peer (P2P) quiescent state is intended to be a quiescent * state for the device for the purposes of managing multiple devices within a * user context where peer-to-peer DMA between devices may be active. The - * RUNNING_P2P states must prevent the device from initiating + * RUNNING_P2P and PRE_COPY_P2P states must prevent the device from initiating * any new P2P DMA transactions. If the device can identify P2P transactions * then it can stop only P2P DMA, otherwise it must stop all DMA. The migration * driver must complete any such outstanding operations prior to completing the @@ -963,6 +1011,8 @@ struct vfio_device_feature_mig_state { * above FSM arcs. As there are multiple paths through the FSM arcs the path * should be selected based on the following rules: * - Select the shortest path. + * - The path cannot have saving group states as interior arcs, only + * starting/end states. * Refer to vfio_mig_get_next_state() for the result of the algorithm. * * The automatic transit through the FSM arcs that make up the combination @@ -976,6 +1026,9 @@ struct vfio_device_feature_mig_state { * support them. The user can discover if these states are supported by using * VFIO_DEVICE_FEATURE_MIGRATION. By using combination transitions the user can * avoid knowing about these optional states if the kernel driver supports them. + * + * Arcs touching PRE_COPY and PRE_COPY_P2P are removed if support for PRE_COPY + * is not present. */ enum vfio_device_mig_state { VFIO_DEVICE_STATE_ERROR = 0, @@ -984,8 +1037,70 @@ enum vfio_device_mig_state { VFIO_DEVICE_STATE_STOP_COPY = 3, VFIO_DEVICE_STATE_RESUMING = 4, VFIO_DEVICE_STATE_RUNNING_P2P = 5, + VFIO_DEVICE_STATE_PRE_COPY = 6, + VFIO_DEVICE_STATE_PRE_COPY_P2P = 7, +}; + +/** + * VFIO_MIG_GET_PRECOPY_INFO - _IO(VFIO_TYPE, VFIO_BASE + 21) + * + * This ioctl is used on the migration data FD in the precopy phase of the + * migration data transfer. It returns an estimate of the current data sizes + * remaining to be transferred. It allows the user to judge when it is + * appropriate to leave PRE_COPY for STOP_COPY. + * + * This ioctl is valid only in PRE_COPY states and kernel driver should + * return -EINVAL from any other migration state. + * + * The vfio_precopy_info data structure returned by this ioctl provides + * estimates of data available from the device during the PRE_COPY states. + * This estimate is split into two categories, initial_bytes and + * dirty_bytes. + * + * The initial_bytes field indicates the amount of initial precopy + * data available from the device. This field should have a non-zero initial + * value and decrease as migration data is read from the device. + * It is recommended to leave PRE_COPY for STOP_COPY only after this field + * reaches zero. Leaving PRE_COPY earlier might make things slower. + * + * The dirty_bytes field tracks device state changes relative to data + * previously retrieved. This field starts at zero and may increase as + * the internal device state is modified or decrease as that modified + * state is read from the device. + * + * Userspace may use the combination of these fields to estimate the + * potential data size available during the PRE_COPY phases, as well as + * trends relative to the rate the device is dirtying its internal + * state, but these fields are not required to have any bearing relative + * to the data size available during the STOP_COPY phase. + * + * Drivers have a lot of flexibility in when and what they transfer during the + * PRE_COPY phase, and how they report this from VFIO_MIG_GET_PRECOPY_INFO. + * + * During pre-copy the migration data FD has a temporary "end of stream" that is + * reached when both initial_bytes and dirty_byte are zero. For instance, this + * may indicate that the device is idle and not currently dirtying any internal + * state. When read() is done on this temporary end of stream the kernel driver + * should return ENOMSG from read(). Userspace can wait for more data (which may + * never come) by using poll. + * + * Once in STOP_COPY the migration data FD has a permanent end of stream + * signaled in the usual way by read() always returning 0 and poll always + * returning readable. ENOMSG may not be returned in STOP_COPY. + * Support for this ioctl is mandatory if a driver claims to support + * VFIO_MIGRATION_PRE_COPY. + * + * Return: 0 on success, -1 and errno set on failure. + */ +struct vfio_precopy_info { + __u32 argsz; + __u32 flags; + __aligned_u64 initial_bytes; + __aligned_u64 dirty_bytes; }; +#define VFIO_MIG_GET_PRECOPY_INFO _IO(VFIO_TYPE, VFIO_BASE + 21) + /* * Upon VFIO_DEVICE_FEATURE_SET, allow the device to be moved into a low power * state with the platform-based power management. Device use of lower power