vfio/migration: Add VFIO migration pre-copy support
Pre-copy support allows the VFIO device data to be transferred while the
VM is running. This helps to accommodate VFIO devices that have a large
amount of data that needs to be transferred, and it can reduce migration
downtime.
Pre-copy support is optional in VFIO migration protocol v2.
Implement pre-copy of VFIO migration protocol v2 and use it for devices
that support it. Full description of it can be found in the following
Linux commit: 4db52602a607 ("vfio: Extend the device migration protocol
with PRE_COPY").
Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Tested-by: YangHang Liu <yanghliu@redhat.com>
Acked-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>
This commit is contained in:
Avihai Horon
Cédric Le Goater
parent
6cd1fe1159
commit
eda7362af9
@ -7,12 +7,14 @@ the guest is running on source host and restoring this saved state on the
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destination host. This document details how saving and restoring of VFIO
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devices is done in QEMU.
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Migration of VFIO devices currently consists of a single stop-and-copy phase.
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During the stop-and-copy phase the guest is stopped and the entire VFIO device
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data is transferred to the destination.
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The pre-copy phase of migration is currently not supported for VFIO devices.
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Support for VFIO pre-copy will be added later on.
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Migration of VFIO devices consists of two phases: the optional pre-copy phase,
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and the stop-and-copy phase. The pre-copy phase is iterative and allows to
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accommodate VFIO devices that have a large amount of data that needs to be
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transferred. The iterative pre-copy phase of migration allows for the guest to
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continue whilst the VFIO device state is transferred to the destination, this
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helps to reduce the total downtime of the VM. VFIO devices opt-in to pre-copy
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support by reporting the VFIO_MIGRATION_PRE_COPY flag in the
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VFIO_DEVICE_FEATURE_MIGRATION ioctl.
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Note that currently VFIO migration is supported only for a single device. This
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is due to VFIO migration's lack of P2P support. However, P2P support is planned
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@ -29,10 +31,20 @@ VFIO implements the device hooks for the iterative approach as follows:
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* A ``load_setup`` function that sets the VFIO device on the destination in
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_RESUMING state.
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* A ``state_pending_estimate`` function that reports an estimate of the
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remaining pre-copy data that the vendor driver has yet to save for the VFIO
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device.
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* A ``state_pending_exact`` function that reads pending_bytes from the vendor
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driver, which indicates the amount of data that the vendor driver has yet to
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save for the VFIO device.
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* An ``is_active_iterate`` function that indicates ``save_live_iterate`` is
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active only when the VFIO device is in pre-copy states.
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* A ``save_live_iterate`` function that reads the VFIO device's data from the
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vendor driver during iterative pre-copy phase.
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* A ``save_state`` function to save the device config space if it is present.
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* A ``save_live_complete_precopy`` function that sets the VFIO device in
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@ -111,8 +123,10 @@ Flow of state changes during Live migration
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===========================================
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Below is the flow of state change during live migration.
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The values in the brackets represent the VM state, the migration state, and
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The values in the parentheses represent the VM state, the migration state, and
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the VFIO device state, respectively.
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The text in the square brackets represents the flow if the VFIO device supports
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pre-copy.
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Live migration save path
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------------------------
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@ -124,11 +138,12 @@ Live migration save path
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migrate_init spawns migration_thread
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Migration thread then calls each device's .save_setup()
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(RUNNING, _SETUP, _RUNNING)
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(RUNNING, _SETUP, _RUNNING [_PRE_COPY])
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(RUNNING, _ACTIVE, _RUNNING)
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If device is active, get pending_bytes by .state_pending_exact()
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(RUNNING, _ACTIVE, _RUNNING [_PRE_COPY])
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If device is active, get pending_bytes by .state_pending_{estimate,exact}()
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If total pending_bytes >= threshold_size, call .save_live_iterate()
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[Data of VFIO device for pre-copy phase is copied]
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Iterate till total pending bytes converge and are less than threshold
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On migration completion, vCPU stops and calls .save_live_complete_precopy for
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@ -492,7 +492,8 @@ static bool vfio_devices_all_dirty_tracking(VFIOContainer *container)
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}
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if (vbasedev->pre_copy_dirty_page_tracking == ON_OFF_AUTO_OFF &&
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migration->device_state == VFIO_DEVICE_STATE_RUNNING) {
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(migration->device_state == VFIO_DEVICE_STATE_RUNNING ||
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migration->device_state == VFIO_DEVICE_STATE_PRE_COPY)) {
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return false;
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}
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}
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@ -537,7 +538,8 @@ static bool vfio_devices_all_running_and_mig_active(VFIOContainer *container)
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return false;
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}
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if (migration->device_state == VFIO_DEVICE_STATE_RUNNING) {
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if (migration->device_state == VFIO_DEVICE_STATE_RUNNING ||
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migration->device_state == VFIO_DEVICE_STATE_PRE_COPY) {
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continue;
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} else {
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return false;
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@ -68,6 +68,8 @@ static const char *mig_state_to_str(enum vfio_device_mig_state state)
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return "STOP_COPY";
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case VFIO_DEVICE_STATE_RESUMING:
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return "RESUMING";
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case VFIO_DEVICE_STATE_PRE_COPY:
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return "PRE_COPY";
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default:
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return "UNKNOWN STATE";
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}
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@ -241,6 +243,25 @@ static int vfio_query_stop_copy_size(VFIODevice *vbasedev,
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return 0;
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}
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static int vfio_query_precopy_size(VFIOMigration *migration)
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{
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struct vfio_precopy_info precopy = {
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.argsz = sizeof(precopy),
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};
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migration->precopy_init_size = 0;
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migration->precopy_dirty_size = 0;
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if (ioctl(migration->data_fd, VFIO_MIG_GET_PRECOPY_INFO, &precopy)) {
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return -errno;
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}
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migration->precopy_init_size = precopy.initial_bytes;
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migration->precopy_dirty_size = precopy.dirty_bytes;
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return 0;
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}
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/* Returns the size of saved data on success and -errno on error */
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static ssize_t vfio_save_block(QEMUFile *f, VFIOMigration *migration)
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{
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@ -249,6 +270,14 @@ static ssize_t vfio_save_block(QEMUFile *f, VFIOMigration *migration)
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data_size = read(migration->data_fd, migration->data_buffer,
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migration->data_buffer_size);
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if (data_size < 0) {
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/*
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* Pre-copy emptied all the device state for now. For more information,
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* please refer to the Linux kernel VFIO uAPI.
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*/
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if (errno == ENOMSG) {
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return 0;
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}
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return -errno;
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}
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if (data_size == 0) {
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@ -265,6 +294,38 @@ static ssize_t vfio_save_block(QEMUFile *f, VFIOMigration *migration)
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return qemu_file_get_error(f) ?: data_size;
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}
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static void vfio_update_estimated_pending_data(VFIOMigration *migration,
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uint64_t data_size)
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{
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if (!data_size) {
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/*
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* Pre-copy emptied all the device state for now, update estimated sizes
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* accordingly.
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*/
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migration->precopy_init_size = 0;
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migration->precopy_dirty_size = 0;
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return;
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}
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if (migration->precopy_init_size) {
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uint64_t init_size = MIN(migration->precopy_init_size, data_size);
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migration->precopy_init_size -= init_size;
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data_size -= init_size;
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}
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migration->precopy_dirty_size -= MIN(migration->precopy_dirty_size,
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data_size);
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}
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static bool vfio_precopy_supported(VFIODevice *vbasedev)
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{
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VFIOMigration *migration = vbasedev->migration;
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return migration->mig_flags & VFIO_MIGRATION_PRE_COPY;
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}
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/* ---------------------------------------------------------------------- */
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static int vfio_save_setup(QEMUFile *f, void *opaque)
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@ -285,6 +346,28 @@ static int vfio_save_setup(QEMUFile *f, void *opaque)
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return -ENOMEM;
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}
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if (vfio_precopy_supported(vbasedev)) {
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int ret;
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switch (migration->device_state) {
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case VFIO_DEVICE_STATE_RUNNING:
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ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_PRE_COPY,
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VFIO_DEVICE_STATE_RUNNING);
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if (ret) {
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return ret;
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}
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vfio_query_precopy_size(migration);
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break;
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case VFIO_DEVICE_STATE_STOP:
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/* vfio_save_complete_precopy() will go to STOP_COPY */
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break;
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default:
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return -EINVAL;
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}
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}
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trace_vfio_save_setup(vbasedev->name, migration->data_buffer_size);
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qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
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@ -299,26 +382,42 @@ static void vfio_save_cleanup(void *opaque)
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g_free(migration->data_buffer);
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migration->data_buffer = NULL;
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migration->precopy_init_size = 0;
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migration->precopy_dirty_size = 0;
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vfio_migration_cleanup(vbasedev);
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trace_vfio_save_cleanup(vbasedev->name);
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}
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static void vfio_state_pending_estimate(void *opaque, uint64_t *must_precopy,
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uint64_t *can_postcopy)
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{
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VFIODevice *vbasedev = opaque;
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VFIOMigration *migration = vbasedev->migration;
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if (migration->device_state != VFIO_DEVICE_STATE_PRE_COPY) {
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return;
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}
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*must_precopy +=
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migration->precopy_init_size + migration->precopy_dirty_size;
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trace_vfio_state_pending_estimate(vbasedev->name, *must_precopy,
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*can_postcopy,
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migration->precopy_init_size,
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migration->precopy_dirty_size);
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}
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/*
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* Migration size of VFIO devices can be as little as a few KBs or as big as
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* many GBs. This value should be big enough to cover the worst case.
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*/
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#define VFIO_MIG_STOP_COPY_SIZE (100 * GiB)
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/*
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* Only exact function is implemented and not estimate function. The reason is
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* that during pre-copy phase of migration the estimate function is called
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* repeatedly while pending RAM size is over the threshold, thus migration
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* can't converge and querying the VFIO device pending data size is useless.
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*/
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static void vfio_state_pending_exact(void *opaque, uint64_t *must_precopy,
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uint64_t *can_postcopy)
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{
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VFIODevice *vbasedev = opaque;
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VFIOMigration *migration = vbasedev->migration;
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uint64_t stop_copy_size = VFIO_MIG_STOP_COPY_SIZE;
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/*
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@ -328,8 +427,48 @@ static void vfio_state_pending_exact(void *opaque, uint64_t *must_precopy,
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vfio_query_stop_copy_size(vbasedev, &stop_copy_size);
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*must_precopy += stop_copy_size;
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if (migration->device_state == VFIO_DEVICE_STATE_PRE_COPY) {
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vfio_query_precopy_size(migration);
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*must_precopy +=
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migration->precopy_init_size + migration->precopy_dirty_size;
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}
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trace_vfio_state_pending_exact(vbasedev->name, *must_precopy, *can_postcopy,
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stop_copy_size);
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stop_copy_size, migration->precopy_init_size,
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migration->precopy_dirty_size);
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}
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static bool vfio_is_active_iterate(void *opaque)
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{
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VFIODevice *vbasedev = opaque;
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VFIOMigration *migration = vbasedev->migration;
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return migration->device_state == VFIO_DEVICE_STATE_PRE_COPY;
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}
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static int vfio_save_iterate(QEMUFile *f, void *opaque)
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{
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VFIODevice *vbasedev = opaque;
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VFIOMigration *migration = vbasedev->migration;
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ssize_t data_size;
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data_size = vfio_save_block(f, migration);
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if (data_size < 0) {
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return data_size;
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}
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qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
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vfio_update_estimated_pending_data(migration, data_size);
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trace_vfio_save_iterate(vbasedev->name, migration->precopy_init_size,
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migration->precopy_dirty_size);
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/*
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* A VFIO device's pre-copy dirty_bytes is not guaranteed to reach zero.
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* Return 1 so following handlers will not be potentially blocked.
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*/
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return 1;
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}
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static int vfio_save_complete_precopy(QEMUFile *f, void *opaque)
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@ -338,7 +477,7 @@ static int vfio_save_complete_precopy(QEMUFile *f, void *opaque)
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ssize_t data_size;
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int ret;
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/* We reach here with device state STOP only */
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/* We reach here with device state STOP or STOP_COPY only */
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ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_STOP_COPY,
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VFIO_DEVICE_STATE_STOP);
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if (ret) {
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@ -457,7 +596,10 @@ static int vfio_load_state(QEMUFile *f, void *opaque, int version_id)
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static const SaveVMHandlers savevm_vfio_handlers = {
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.save_setup = vfio_save_setup,
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.save_cleanup = vfio_save_cleanup,
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.state_pending_estimate = vfio_state_pending_estimate,
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.state_pending_exact = vfio_state_pending_exact,
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.is_active_iterate = vfio_is_active_iterate,
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.save_live_iterate = vfio_save_iterate,
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.save_live_complete_precopy = vfio_save_complete_precopy,
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.save_state = vfio_save_state,
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.load_setup = vfio_load_setup,
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@ -470,13 +612,18 @@ static const SaveVMHandlers savevm_vfio_handlers = {
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static void vfio_vmstate_change(void *opaque, bool running, RunState state)
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{
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VFIODevice *vbasedev = opaque;
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VFIOMigration *migration = vbasedev->migration;
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enum vfio_device_mig_state new_state;
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int ret;
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if (running) {
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new_state = VFIO_DEVICE_STATE_RUNNING;
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} else {
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new_state = VFIO_DEVICE_STATE_STOP;
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new_state =
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(migration->device_state == VFIO_DEVICE_STATE_PRE_COPY &&
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(state == RUN_STATE_FINISH_MIGRATE || state == RUN_STATE_PAUSED)) ?
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VFIO_DEVICE_STATE_STOP_COPY :
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VFIO_DEVICE_STATE_STOP;
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}
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/*
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@ -162,6 +162,8 @@ vfio_save_block(const char *name, int data_size) " (%s) data_size %d"
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vfio_save_cleanup(const char *name) " (%s)"
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vfio_save_complete_precopy(const char *name, int ret) " (%s) ret %d"
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vfio_save_device_config_state(const char *name) " (%s)"
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vfio_save_iterate(const char *name, uint64_t precopy_init_size, uint64_t precopy_dirty_size) " (%s) precopy initial size 0x%"PRIx64" precopy dirty size 0x%"PRIx64
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vfio_save_setup(const char *name, uint64_t data_buffer_size) " (%s) data buffer size 0x%"PRIx64
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vfio_state_pending_exact(const char *name, uint64_t precopy, uint64_t postcopy, uint64_t stopcopy_size) " (%s) precopy 0x%"PRIx64" postcopy 0x%"PRIx64" stopcopy size 0x%"PRIx64
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vfio_state_pending_estimate(const char *name, uint64_t precopy, uint64_t postcopy, uint64_t precopy_init_size, uint64_t precopy_dirty_size) " (%s) precopy 0x%"PRIx64" postcopy 0x%"PRIx64" precopy initial size 0x%"PRIx64" precopy dirty size 0x%"PRIx64
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vfio_state_pending_exact(const char *name, uint64_t precopy, uint64_t postcopy, uint64_t stopcopy_size, uint64_t precopy_init_size, uint64_t precopy_dirty_size) " (%s) precopy 0x%"PRIx64" postcopy 0x%"PRIx64" stopcopy size 0x%"PRIx64" precopy initial size 0x%"PRIx64" precopy dirty size 0x%"PRIx64
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vfio_vmstate_change(const char *name, int running, const char *reason, const char *dev_state) " (%s) running %d reason %s device state %s"
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@ -67,6 +67,8 @@ typedef struct VFIOMigration {
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void *data_buffer;
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size_t data_buffer_size;
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uint64_t mig_flags;
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uint64_t precopy_init_size;
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uint64_t precopy_dirty_size;
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} VFIOMigration;
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typedef struct VFIOAddressSpace {
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