From 169dc1bb051b3aebc571936d956b49ba0621ae43 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?C=C3=A9dric=20Le=20Goater?= Date: Wed, 12 Jul 2023 17:46:57 +0200 Subject: [PATCH 16/37] vfio/migration: Add support for switchover ack capability MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit RH-Author: Cédric Le Goater RH-MergeRequest: 179: vfio: live migration support RH-Bugzilla: 2192818 RH-Acked-by: Eric Auger RH-Acked-by: Miroslav Rezanina RH-Commit: [14/28] b3bd2eb2d0ca49ff05a0a82ae5bb956a354aed47 (clegoate/qemu-kvm-c9s) Bugzilla: https://bugzilla.redhat.com/2192818 commit 745c42912a04 Author: Avihai Horon Date: Wed Jun 21 14:12:01 2023 +0300 vfio/migration: Add support for switchover ack capability Loading of a VFIO device's data can take a substantial amount of time as the device may need to allocate resources, prepare internal data structures, etc. This can increase migration downtime, especially for VFIO devices with a lot of resources. To solve this, VFIO migration uAPI defines "initial bytes" as part of its precopy data stream. Initial bytes can be used in various ways to improve VFIO migration performance. For example, it can be used to transfer device metadata to pre-allocate resources in the destination. However, for this to work we need to make sure that all initial bytes are sent and loaded in the destination before the source VM is stopped. Use migration switchover ack capability to make sure a VFIO device's initial bytes are sent and loaded in the destination before the source stops the VM and attempts to complete the migration. This can significantly reduce migration downtime for some devices. Signed-off-by: Avihai Horon Reviewed-by: Cédric Le Goater Tested-by: YangHang Liu Acked-by: Alex Williamson Signed-off-by: Cédric Le Goater Signed-off-by: Cédric Le Goater --- docs/devel/vfio-migration.rst | 10 +++++++++ hw/vfio/migration.c | 39 ++++++++++++++++++++++++++++++++++- include/hw/vfio/vfio-common.h | 1 + 3 files changed, 49 insertions(+), 1 deletion(-) diff --git a/docs/devel/vfio-migration.rst b/docs/devel/vfio-migration.rst index e896b2a673..b433cb5bb2 100644 --- a/docs/devel/vfio-migration.rst +++ b/docs/devel/vfio-migration.rst @@ -16,6 +16,13 @@ helps to reduce the total downtime of the VM. VFIO devices opt-in to pre-copy support by reporting the VFIO_MIGRATION_PRE_COPY flag in the VFIO_DEVICE_FEATURE_MIGRATION ioctl. +When pre-copy is supported, it's possible to further reduce downtime by +enabling "switchover-ack" migration capability. +VFIO migration uAPI defines "initial bytes" as part of its pre-copy data stream +and recommends that the initial bytes are sent and loaded in the destination +before stopping the source VM. Enabling this migration capability will +guarantee that and thus, can potentially reduce downtime even further. + Note that currently VFIO migration is supported only for a single device. This is due to VFIO migration's lack of P2P support. However, P2P support is planned to be added later on. @@ -45,6 +52,9 @@ VFIO implements the device hooks for the iterative approach as follows: * A ``save_live_iterate`` function that reads the VFIO device's data from the vendor driver during iterative pre-copy phase. +* A ``switchover_ack_needed`` function that checks if the VFIO device uses + "switchover-ack" migration capability when this capability is enabled. + * A ``save_state`` function to save the device config space if it is present. * A ``save_live_complete_precopy`` function that sets the VFIO device in diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c index d8f6a22ae1..acbf0bb7ab 100644 --- a/hw/vfio/migration.c +++ b/hw/vfio/migration.c @@ -18,6 +18,8 @@ #include "sysemu/runstate.h" #include "hw/vfio/vfio-common.h" #include "migration/migration.h" +#include "migration/options.h" +#include "migration/savevm.h" #include "migration/vmstate.h" #include "migration/qemu-file.h" #include "migration/register.h" @@ -45,6 +47,7 @@ #define VFIO_MIG_FLAG_DEV_CONFIG_STATE (0xffffffffef100002ULL) #define VFIO_MIG_FLAG_DEV_SETUP_STATE (0xffffffffef100003ULL) #define VFIO_MIG_FLAG_DEV_DATA_STATE (0xffffffffef100004ULL) +#define VFIO_MIG_FLAG_DEV_INIT_DATA_SENT (0xffffffffef100005ULL) /* * This is an arbitrary size based on migration of mlx5 devices, where typically @@ -384,6 +387,7 @@ static void vfio_save_cleanup(void *opaque) migration->data_buffer = NULL; migration->precopy_init_size = 0; migration->precopy_dirty_size = 0; + migration->initial_data_sent = false; vfio_migration_cleanup(vbasedev); trace_vfio_save_cleanup(vbasedev->name); } @@ -457,10 +461,17 @@ static int vfio_save_iterate(QEMUFile *f, void *opaque) if (data_size < 0) { return data_size; } - qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE); vfio_update_estimated_pending_data(migration, data_size); + if (migrate_switchover_ack() && !migration->precopy_init_size && + !migration->initial_data_sent) { + qemu_put_be64(f, VFIO_MIG_FLAG_DEV_INIT_DATA_SENT); + migration->initial_data_sent = true; + } else { + qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE); + } + trace_vfio_save_iterate(vbasedev->name, migration->precopy_init_size, migration->precopy_dirty_size); @@ -579,6 +590,24 @@ static int vfio_load_state(QEMUFile *f, void *opaque, int version_id) } break; } + case VFIO_MIG_FLAG_DEV_INIT_DATA_SENT: + { + if (!vfio_precopy_supported(vbasedev) || + !migrate_switchover_ack()) { + error_report("%s: Received INIT_DATA_SENT but switchover ack " + "is not used", vbasedev->name); + return -EINVAL; + } + + ret = qemu_loadvm_approve_switchover(); + if (ret) { + error_report( + "%s: qemu_loadvm_approve_switchover failed, err=%d (%s)", + vbasedev->name, ret, strerror(-ret)); + } + + return ret; + } default: error_report("%s: Unknown tag 0x%"PRIx64, vbasedev->name, data); return -EINVAL; @@ -593,6 +622,13 @@ static int vfio_load_state(QEMUFile *f, void *opaque, int version_id) return ret; } +static bool vfio_switchover_ack_needed(void *opaque) +{ + VFIODevice *vbasedev = opaque; + + return vfio_precopy_supported(vbasedev); +} + static const SaveVMHandlers savevm_vfio_handlers = { .save_setup = vfio_save_setup, .save_cleanup = vfio_save_cleanup, @@ -605,6 +641,7 @@ static const SaveVMHandlers savevm_vfio_handlers = { .load_setup = vfio_load_setup, .load_cleanup = vfio_load_cleanup, .load_state = vfio_load_state, + .switchover_ack_needed = vfio_switchover_ack_needed, }; /* ---------------------------------------------------------------------- */ diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h index 1db901c194..3dc5f2104c 100644 --- a/include/hw/vfio/vfio-common.h +++ b/include/hw/vfio/vfio-common.h @@ -69,6 +69,7 @@ typedef struct VFIOMigration { uint64_t mig_flags; uint64_t precopy_init_size; uint64_t precopy_dirty_size; + bool initial_data_sent; } VFIOMigration; typedef struct VFIOAddressSpace { -- 2.39.3