[PATCH v4 0/9] migration: Add switchover ack capability and VFIO precopy support

[PATCH v4 0/9] migration: Add switchover ack capability and VFIO precopy support

[Avihai Horon]

Hello everyone,

This is v4 of the switchover ack series.

Changes from v3 [5]:
* Rebased on latest master branch.
* Simplified switchover ack logic (call switchover_ack_needed only in
  destination). (Peter)
* Moved caching of VFIO migration flags to a separate patch. (Cedric)
* Moved adding of x-allow-pre-copy property to a separate patch. (Cedric)
* Reset VFIOMigration->precopy_{init,dirty}_size in vfio_query_precopy_size()
  and in vfio_save_cleanup(). (Cedric)
* Added a reference to VFIO uAPI in vfio_save_block() ENOMSG comment. (Cedric)
* Added VFIOMigration->precopy_{init,dirty}_size to trace_vfio_save_iterate(). (Cedric)
* Adapted VFIO migration to switchover ack logic simplification:
  - Checked migrate_switchover_ack() in vfio_{save,load}_setup() and set
    VFIOMigration->switchover_ack_needed accordingly.
  - vfio_switchover_ack_needed() doesn't set VFIOMigration->switchover_ack_needed
    and only returns its value.
* Move VFIOMigration->switchover_ack_needed = false to vfio_migration_cleanup()
  so it will be set to false both in src and dest.
* Fixed a few typos/coding style. (Peter/Cedric)
* Added R-b/A-b (didn't add Cedric's R-b on patch #7 as switchover ack
  changes in patch #2 introduced some changes to patch #7 as well).

Changes from v2 [4]:
* Rebased on latest master branch.
* Changed the capability name to "switchover-ack" and the related
  code/docs accordingly. (Peter)
* Added a counter for the number of switchover ack users in the source
  and used it to skip switchover ack if there are no users (instead of
  setting the switchover acked flag to true). (Peter)
* Added R-bs.

Changes from v1 [3]:
* Rebased on latest master branch.
* Updated to latest QAPI doc comment conventions and refined
  QAPI docs and capability error message. (Markus)
* Followed Peter/Juan suggestion and removed the handshake between
  source and destination.
  Now the capability must be set on both source and destination.
  Compatibility of this feature between different QEMU versions or
  different host capabilities (i.e., kernel) is achieved in the regular
  way of device properties and hw_comapt_x_y.
* Replaced is_initial_data_active() and initial_data_loaded()
  SaveVMHandlers handlers with a notification mechanism. (Peter)
* Set the capability also in destination in the migration test.
* Added VFIO device property x-allow-pre-copy to be able to preserve
  compatibility between different QEMU versions or different host
  capabilities (i.e., kernel).
* Changed VFIO precopy initial data implementation according to the
  above changes.
* Documented VFIO precopy initial data support in VFIO migration
  documentation.
* Added R-bs.

===

This series adds a new migration capability called "switchover ack". The
purpose of this capability is to reduce migration downtime in cases
where loading of migration data in the destination can take a lot of
time, such as with VFIO migration data.

The series then moves to add precopy support and switchover ack support
for VFIO migration.

Switchover ack is used by VFIO migration, but other migrated devices can
add support for it and use it as well.

=== Background ===

Migration downtime estimation is calculated based on bandwidth and
remaining migration data. This assumes that loading of migration data in
the destination takes a negligible amount of time and that downtime
depends only on network speed.

While this may be true for RAM, it's not necessarily true for other
migrated devices. For example, loading the data of a VFIO device in the
destination might require from the device to allocate resources and
prepare internal data structures which can take a significant amount of
time to do.

This poses a problem, as the source may think that the remaining
migration data is small enough to meet the downtime limit, so it will
stop the VM and complete the migration, but in fact sending and loading
the data in the destination may take longer than the downtime limit.

To solve this, VFIO migration uAPI defines "initial bytes" as part of
its precopy stream [1]. 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.

The new switchover ack migration capability helps us achieve this.
It prevents the source from stopping the VM and completing the migration
until an ACK is received from the destination that it's OK to do so.
Thus, a VFIO device can make sure that its initial bytes were sent
and loaded in the destination before the source VM is stopped.

Note that this relies on the return path capability to communicate from
the destination back to the source.

=== Flow of operation ===

To use switchover ack, the capability must be enabled in both the source
and the destination.

During migration setup, migration code in the destination calls the
switchover_ack_needed() SaveVMHandlers handler of the migrated devices
to check if switchover ack is used by them.
A "switchover_ack_pending_num" counter is increased for each migrated
device that supports this feature. It will be used later to mark when an
ACK should be sent to the source.

Migration is active and the source starts to send precopy data as usual.
In the destination, when a migrated device thinks it's OK to do
switchover, it notifies the migration code about it and the
"switchover_ack_pending_num" counter is decreased. For example, for a
VFIO device it's when the device receives and loads its initial bytes.

When the "switchover_ack_pending_num" counter reaches zero, it means
that all devices agree to do switchover and an ACK is sent to the
source, which will now be able to complete the migration when
appropriate.

=== Test results ===

The below table shows the downtime of two identical migrations. In the
first migration swithcover ack is disabled and in the second it is
enabled. The migrated VM is assigned with a mlx5 VFIO device which has
300MB of device data to be migrated.

+----------------------+-----------------------+----------+
|    Switchover ack    | VFIO device data size | Downtime |
+----------------------+-----------------------+----------+
|       Disabled       |         300MB         |  1900ms  |
|       Enabled        |         300MB         |  420ms   |
+----------------------+-----------------------+----------+

Switchover ack gives a roughly 4.5 times improvement in downtime.
The 1480ms difference is time that is used for resource allocation for
the VFIO device in the destination. Without switchover ack, this time is
spent when the source VM is stopped and thus the downtime is much
higher. With switchover ack, the time is spent when the source VM is
still running.

=== Patch breakdown ===

- Patches 1-4 add the switchover ack capability.
- Patches 5-8 add VFIO migration precopy support. Similar version of
  them was previously sent here [2].
- Patch 9 adds switchover ack support for VFIO migration.

Thanks for reviewing!

[1]
https://elixir.bootlin.com/linux/latest/source/include/uapi/linux/vfio.h#L1048

[2]
https://lore.kernel.org/qemu-devel/20230222174915.5647-3-avihaih@nvidia.com/

[3]
https://lore.kernel.org/qemu-devel/20230501140141.11743-1-avihaih@nvidia.com/

[4]
https://lore.kernel.org/qemu-devel/20230517155219.10691-1-avihaih@nvidia.com/

[5]
https://lore.kernel.org/qemu-devel/20230521151808.24804-1-avihaih@nvidia.com/

Avihai Horon (9):
  migration: Add switchover ack capability
  migration: Implement switchover ack logic
  migration: Enable switchover ack capability
  tests: Add migration switchover ack capability test
  vfio/migration: Refactor vfio_save_block() to return saved data size
  vfio/migration: Store VFIO migration flags in VFIOMigration
  vfio/migration: Add VFIO migration pre-copy support
  vfio/migration: Add x-allow-pre-copy VFIO device property
  vfio/migration: Add support for switchover ack capability

 docs/devel/vfio-migration.rst |  45 +++++--
 qapi/migration.json           |  12 +-
 include/hw/vfio/vfio-common.h |   6 +
 include/migration/register.h  |   2 +
 migration/migration.h         |  14 +++
 migration/options.h           |   1 +
 migration/savevm.h            |   1 +
 hw/core/machine.c             |   1 +
 hw/vfio/common.c              |   6 +-
 hw/vfio/migration.c           | 230 +++++++++++++++++++++++++++++++---
 hw/vfio/pci.c                 |   2 +
 migration/migration.c         |  32 ++++-
 migration/options.c           |  17 +++
 migration/savevm.c            |  54 ++++++++
 tests/qtest/migration-test.c  |  26 ++++
 hw/vfio/trace-events          |   4 +-
 migration/trace-events        |   3 +
 17 files changed, 423 insertions(+), 33 deletions(-)

-- 
2.26.3

[PATCH v4 1/9] migration: Add switchover ack capability

[Avihai Horon]

Migration downtime estimation is calculated based on bandwidth and
remaining migration data. This assumes that loading of migration data in
the destination takes a negligible amount of time and that downtime
depends only on network speed.

While this may be true for RAM, it's not necessarily true for other
migrated devices. For example, loading the data of a VFIO device in the
destination might require from the device to allocate resources, prepare
internal data structures and so on. These operations can take a
significant amount of time which can increase migration downtime.

This patch adds a new capability "switchover ack" that prevents the
source from stopping the VM and completing the migration until an ACK
is received from the destination that it's OK to do so.

This can be used by migrated devices in various ways to reduce downtime.
For example, a device can send initial precopy metadata to pre-allocate
resources in the destination and use this capability to make sure that
the pre-allocation is completed before the source VM is stopped, so it
will have full effect.

This new capability relies on the return path capability to communicate
from the destination back to the source.

The actual implementation of the capability will be added in the
following patches.

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
---
 qapi/migration.json | 12 +++++++++++-
 migration/options.h |  1 +
 migration/options.c | 21 +++++++++++++++++++++
 3 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/qapi/migration.json b/qapi/migration.json
index 179af0c4d8..061ea512e0 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -487,6 +487,16 @@
 #     and should not affect the correctness of postcopy migration.
 #     (since 7.1)
 #
+# @switchover-ack: If enabled, migration will not stop the source VM
+#     and complete the migration until an ACK is received from the
+#     destination that it's OK to do so.  Exactly when this ACK is
+#     sent depends on the migrated devices that use this feature.
+#     For example, a device can use it to make sure some of its data
+#     is sent and loaded in the destination before doing switchover.
+#     This can reduce downtime if devices that support this capability
+#     are present.  'return-path' capability must be enabled to use
+#     it.  (since 8.1)
+#
 # Features:
 #
 # @unstable: Members @x-colo and @x-ignore-shared are experimental.
@@ -502,7 +512,7 @@
            'dirty-bitmaps', 'postcopy-blocktime', 'late-block-activate',
            { 'name': 'x-ignore-shared', 'features': [ 'unstable' ] },
            'validate-uuid', 'background-snapshot',
-           'zero-copy-send', 'postcopy-preempt'] }
+           'zero-copy-send', 'postcopy-preempt', 'switchover-ack'] }
 
 ##
 # @MigrationCapabilityStatus:
diff --git a/migration/options.h b/migration/options.h
index 45991af3c2..9aaf363322 100644
--- a/migration/options.h
+++ b/migration/options.h
@@ -40,6 +40,7 @@ bool migrate_postcopy_ram(void);
 bool migrate_rdma_pin_all(void);
 bool migrate_release_ram(void);
 bool migrate_return_path(void);
+bool migrate_switchover_ack(void);
 bool migrate_validate_uuid(void);
 bool migrate_xbzrle(void);
 bool migrate_zero_blocks(void);
diff --git a/migration/options.c b/migration/options.c
index b62ab30cd5..16007afca6 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -185,6 +185,8 @@ Property migration_properties[] = {
     DEFINE_PROP_MIG_CAP("x-zero-copy-send",
             MIGRATION_CAPABILITY_ZERO_COPY_SEND),
 #endif
+    DEFINE_PROP_MIG_CAP("x-switchover-ack",
+                        MIGRATION_CAPABILITY_SWITCHOVER_ACK),
 
     DEFINE_PROP_END_OF_LIST(),
 };
@@ -308,6 +310,13 @@ bool migrate_return_path(void)
     return s->capabilities[MIGRATION_CAPABILITY_RETURN_PATH];
 }
 
+bool migrate_switchover_ack(void)
+{
+    MigrationState *s = migrate_get_current();
+
+    return s->capabilities[MIGRATION_CAPABILITY_SWITCHOVER_ACK];
+}
+
 bool migrate_validate_uuid(void)
 {
     MigrationState *s = migrate_get_current();
@@ -547,6 +556,18 @@ bool migrate_caps_check(bool *old_caps, bool *new_caps, Error **errp)
         }
     }
 
+    if (new_caps[MIGRATION_CAPABILITY_SWITCHOVER_ACK]) {
+        if (!new_caps[MIGRATION_CAPABILITY_RETURN_PATH]) {
+            error_setg(errp, "Capability 'switchover-ack' requires capability "
+                             "'return-path'");
+            return false;
+        }
+
+        /* Disable this capability until it's implemented */
+        error_setg(errp, "'switchover-ack' is not implemented yet");
+        return false;
+    }
+
     return true;
 }
 
-- 
2.26.3

[PATCH v4 2/9] migration: Implement switchover ack logic

[Avihai Horon]

Implement switchover ack logic. This prevents the source from stopping
the VM and completing the migration until an ACK is received from the
destination that it's OK to do so.

To achieve this, a new SaveVMHandlers handler switchover_ack_needed()
and a new return path message MIG_RP_MSG_SWITCHOVER_ACK are added.

The switchover_ack_needed() handler is called during migration setup in
the destination to check if switchover ack is used by the migrated
device.

When switchover is approved by all migrated devices in the destination
that support this capability, the MIG_RP_MSG_SWITCHOVER_ACK return path
message is sent to the source to notify it that it's OK to do
switchover.

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
---
 include/migration/register.h |  2 ++
 migration/migration.h        | 14 ++++++++++
 migration/savevm.h           |  1 +
 migration/migration.c        | 32 +++++++++++++++++++--
 migration/savevm.c           | 54 ++++++++++++++++++++++++++++++++++++
 migration/trace-events       |  3 ++
 6 files changed, 104 insertions(+), 2 deletions(-)

diff --git a/include/migration/register.h b/include/migration/register.h
index a8dfd8fefd..90914f32f5 100644
--- a/include/migration/register.h
+++ b/include/migration/register.h
@@ -71,6 +71,8 @@ typedef struct SaveVMHandlers {
     int (*load_cleanup)(void *opaque);
     /* Called when postcopy migration wants to resume from failure */
     int (*resume_prepare)(MigrationState *s, void *opaque);
+    /* Checks if switchover ack should be used. Called only in dest */
+    bool (*switchover_ack_needed)(void *opaque);
 } SaveVMHandlers;
 
 int register_savevm_live(const char *idstr,
diff --git a/migration/migration.h b/migration/migration.h
index 48a46123a0..1e92ba7b1d 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -209,6 +209,13 @@ struct MigrationIncomingState {
      * contains valid information.
      */
     QemuMutex page_request_mutex;
+
+    /*
+     * Number of devices that have yet to approve switchover. When this reaches
+     * zero an ACK that it's OK to do switchover is sent to the source. No lock
+     * is needed as this field is updated serially.
+     */
+    unsigned int switchover_ack_pending_num;
 };
 
 MigrationIncomingState *migration_incoming_get_current(void);
@@ -437,6 +444,12 @@ struct MigrationState {
 
     /* QEMU_VM_VMDESCRIPTION content filled for all non-iterable devices. */
     JSONWriter *vmdesc;
+
+    /*
+     * Indicates whether an ACK from the destination that it's OK to do
+     * switchover has been received.
+     */
+    bool switchover_acked;
 };
 
 void migrate_set_state(int *state, int old_state, int new_state);
@@ -477,6 +490,7 @@ int migrate_send_rp_message_req_pages(MigrationIncomingState *mis,
 void migrate_send_rp_recv_bitmap(MigrationIncomingState *mis,
                                  char *block_name);
 void migrate_send_rp_resume_ack(MigrationIncomingState *mis, uint32_t value);
+int migrate_send_rp_switchover_ack(MigrationIncomingState *mis);
 
 void dirty_bitmap_mig_before_vm_start(void);
 void dirty_bitmap_mig_cancel_outgoing(void);
diff --git a/migration/savevm.h b/migration/savevm.h
index fb636735f0..e894bbc143 100644
--- a/migration/savevm.h
+++ b/migration/savevm.h
@@ -65,6 +65,7 @@ int qemu_loadvm_state(QEMUFile *f);
 void qemu_loadvm_state_cleanup(void);
 int qemu_loadvm_state_main(QEMUFile *f, MigrationIncomingState *mis);
 int qemu_load_device_state(QEMUFile *f);
+int qemu_loadvm_approve_switchover(void);
 int qemu_savevm_state_complete_precopy_non_iterable(QEMUFile *f,
         bool in_postcopy, bool inactivate_disks);
 
diff --git a/migration/migration.c b/migration/migration.c
index 5de7f734b9..c73261118c 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -78,6 +78,7 @@ enum mig_rp_message_type {
     MIG_RP_MSG_REQ_PAGES,    /* data (start: be64, len: be32) */
     MIG_RP_MSG_RECV_BITMAP,  /* send recved_bitmap back to source */
     MIG_RP_MSG_RESUME_ACK,   /* tell source that we are ready to resume */
+    MIG_RP_MSG_SWITCHOVER_ACK, /* Tell source it's OK to do switchover */
 
     MIG_RP_MSG_MAX
 };
@@ -760,6 +761,11 @@ bool migration_has_all_channels(void)
     return true;
 }
 
+int migrate_send_rp_switchover_ack(MigrationIncomingState *mis)
+{
+    return migrate_send_rp_message(mis, MIG_RP_MSG_SWITCHOVER_ACK, 0, NULL);
+}
+
 /*
  * Send a 'SHUT' message on the return channel with the given value
  * to indicate that we've finished with the RP.  Non-0 value indicates
@@ -1405,6 +1411,7 @@ void migrate_init(MigrationState *s)
     s->vm_was_running = false;
     s->iteration_initial_bytes = 0;
     s->threshold_size = 0;
+    s->switchover_acked = false;
 }
 
 int migrate_add_blocker_internal(Error *reason, Error **errp)
@@ -1721,6 +1728,7 @@ static struct rp_cmd_args {
     [MIG_RP_MSG_REQ_PAGES_ID]   = { .len = -1, .name = "REQ_PAGES_ID" },
     [MIG_RP_MSG_RECV_BITMAP]    = { .len = -1, .name = "RECV_BITMAP" },
     [MIG_RP_MSG_RESUME_ACK]     = { .len =  4, .name = "RESUME_ACK" },
+    [MIG_RP_MSG_SWITCHOVER_ACK] = { .len =  0, .name = "SWITCHOVER_ACK" },
     [MIG_RP_MSG_MAX]            = { .len = -1, .name = "MAX" },
 };
 
@@ -1959,6 +1967,11 @@ retry:
             }
             break;
 
+        case MIG_RP_MSG_SWITCHOVER_ACK:
+            ms->switchover_acked = true;
+            trace_source_return_path_thread_switchover_acked();
+            break;
+
         default:
             break;
         }
@@ -2700,6 +2713,20 @@ static void migration_update_counters(MigrationState *s,
                               bandwidth, s->threshold_size);
 }
 
+static bool migration_can_switchover(MigrationState *s)
+{
+    if (!migrate_switchover_ack()) {
+        return true;
+    }
+
+    /* No reason to wait for switchover ACK if VM is stopped */
+    if (!runstate_is_running()) {
+        return true;
+    }
+
+    return s->switchover_acked;
+}
+
 /* Migration thread iteration status */
 typedef enum {
     MIG_ITERATE_RESUME,         /* Resume current iteration */
@@ -2715,6 +2742,7 @@ static MigIterateState migration_iteration_run(MigrationState *s)
 {
     uint64_t must_precopy, can_postcopy;
     bool in_postcopy = s->state == MIGRATION_STATUS_POSTCOPY_ACTIVE;
+    bool can_switchover = migration_can_switchover(s);
 
     qemu_savevm_state_pending_estimate(&must_precopy, &can_postcopy);
     uint64_t pending_size = must_precopy + can_postcopy;
@@ -2727,14 +2755,14 @@ static MigIterateState migration_iteration_run(MigrationState *s)
         trace_migrate_pending_exact(pending_size, must_precopy, can_postcopy);
     }
 
-    if (!pending_size || pending_size < s->threshold_size) {
+    if ((!pending_size || pending_size < s->threshold_size) && can_switchover) {
         trace_migration_thread_low_pending(pending_size);
         migration_completion(s);
         return MIG_ITERATE_BREAK;
     }
 
     /* Still a significant amount to transfer */
-    if (!in_postcopy && must_precopy <= s->threshold_size &&
+    if (!in_postcopy && must_precopy <= s->threshold_size && can_switchover &&
         qatomic_read(&s->start_postcopy)) {
         if (postcopy_start(s)) {
             error_report("%s: postcopy failed to start", __func__);
diff --git a/migration/savevm.c b/migration/savevm.c
index 03795ce8dc..285b814726 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2360,6 +2360,21 @@ static int loadvm_process_command(QEMUFile *f)
             error_report("CMD_OPEN_RETURN_PATH failed");
             return -1;
         }
+
+        /*
+         * Switchover ack is enabled but no device uses it, so send an ACK to
+         * source that it's OK to switchover. Do it here, after return path has
+         * been created.
+         */
+        if (migrate_switchover_ack() && !mis->switchover_ack_pending_num) {
+            int ret = migrate_send_rp_switchover_ack(mis);
+            if (ret) {
+                error_report(
+                    "Could not send switchover ack RP MSG, err %d (%s)", ret,
+                    strerror(-ret));
+                return ret;
+            }
+        }
         break;
 
     case MIG_CMD_PING:
@@ -2586,6 +2601,23 @@ static int qemu_loadvm_state_header(QEMUFile *f)
     return 0;
 }
 
+static void qemu_loadvm_state_switchover_ack_needed(MigrationIncomingState *mis)
+{
+    SaveStateEntry *se;
+
+    QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
+        if (!se->ops || !se->ops->switchover_ack_needed) {
+            continue;
+        }
+
+        if (se->ops->switchover_ack_needed(se->opaque)) {
+            mis->switchover_ack_pending_num++;
+        }
+    }
+
+    trace_loadvm_state_switchover_ack_needed(mis->switchover_ack_pending_num);
+}
+
 static int qemu_loadvm_state_setup(QEMUFile *f)
 {
     SaveStateEntry *se;
@@ -2789,6 +2821,10 @@ int qemu_loadvm_state(QEMUFile *f)
         return -EINVAL;
     }
 
+    if (migrate_switchover_ack()) {
+        qemu_loadvm_state_switchover_ack_needed(mis);
+    }
+
     cpu_synchronize_all_pre_loadvm();
 
     ret = qemu_loadvm_state_main(f, mis);
@@ -2862,6 +2898,24 @@ int qemu_load_device_state(QEMUFile *f)
     return 0;
 }
 
+int qemu_loadvm_approve_switchover(void)
+{
+    MigrationIncomingState *mis = migration_incoming_get_current();
+
+    if (!mis->switchover_ack_pending_num) {
+        return -EINVAL;
+    }
+
+    mis->switchover_ack_pending_num--;
+    trace_loadvm_approve_switchover(mis->switchover_ack_pending_num);
+
+    if (mis->switchover_ack_pending_num) {
+        return 0;
+    }
+
+    return migrate_send_rp_switchover_ack(mis);
+}
+
 bool save_snapshot(const char *name, bool overwrite, const char *vmstate,
                   bool has_devices, strList *devices, Error **errp)
 {
diff --git a/migration/trace-events b/migration/trace-events
index cdaef7a1ea..5259c1044b 100644
--- a/migration/trace-events
+++ b/migration/trace-events
@@ -7,6 +7,7 @@ qemu_loadvm_state_section_partend(uint32_t section_id) "%u"
 qemu_loadvm_state_post_main(int ret) "%d"
 qemu_loadvm_state_section_startfull(uint32_t section_id, const char *idstr, uint32_t instance_id, uint32_t version_id) "%u(%s) %u %u"
 qemu_savevm_send_packaged(void) ""
+loadvm_state_switchover_ack_needed(unsigned int switchover_ack_pending_num) "Switchover ack pending num=%u"
 loadvm_state_setup(void) ""
 loadvm_state_cleanup(void) ""
 loadvm_handle_cmd_packaged(unsigned int length) "%u"
@@ -23,6 +24,7 @@ loadvm_postcopy_ram_handle_discard_end(void) ""
 loadvm_postcopy_ram_handle_discard_header(const char *ramid, uint16_t len) "%s: %ud"
 loadvm_process_command(const char *s, uint16_t len) "com=%s len=%d"
 loadvm_process_command_ping(uint32_t val) "0x%x"
+loadvm_approve_switchover(unsigned int switchover_ack_pending_num) "Switchover ack pending num=%u"
 postcopy_ram_listen_thread_exit(void) ""
 postcopy_ram_listen_thread_start(void) ""
 qemu_savevm_send_postcopy_advise(void) ""
@@ -180,6 +182,7 @@ source_return_path_thread_loop_top(void) ""
 source_return_path_thread_pong(uint32_t val) "0x%x"
 source_return_path_thread_shut(uint32_t val) "0x%x"
 source_return_path_thread_resume_ack(uint32_t v) "%"PRIu32
+source_return_path_thread_switchover_acked(void) ""
 migration_thread_low_pending(uint64_t pending) "%" PRIu64
 migrate_transferred(uint64_t tranferred, uint64_t time_spent, uint64_t bandwidth, uint64_t size) "transferred %" PRIu64 " time_spent %" PRIu64 " bandwidth %" PRIu64 " max_size %" PRId64
 process_incoming_migration_co_end(int ret, int ps) "ret=%d postcopy-state=%d"
-- 
2.26.3

[PATCH v4 3/9] migration: Enable switchover ack capability

[Avihai Horon]

Now that switchover ack logic has been implemented, enable the
capability.

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
---
 migration/options.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/migration/options.c b/migration/options.c
index 16007afca6..5a9505adf7 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -562,10 +562,6 @@ bool migrate_caps_check(bool *old_caps, bool *new_caps, Error **errp)
                              "'return-path'");
             return false;
         }
-
-        /* Disable this capability until it's implemented */
-        error_setg(errp, "'switchover-ack' is not implemented yet");
-        return false;
     }
 
     return true;
-- 
2.26.3

[PATCH v4 4/9] tests: Add migration switchover ack capability test

[Avihai Horon]

Add migration switchover ack capability test. The test runs without
devices that support this capability, but is still useful to make sure
it didn't break anything.

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
---
 tests/qtest/migration-test.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/tests/qtest/migration-test.c b/tests/qtest/migration-test.c
index b99b49a314..d246a5bbc5 100644
--- a/tests/qtest/migration-test.c
+++ b/tests/qtest/migration-test.c
@@ -1648,6 +1648,28 @@ static void test_precopy_tcp_plain(void)
     test_precopy_common(&args);
 }
 
+static void *test_migrate_switchover_ack_start(QTestState *from, QTestState *to)
+{
+
+    migrate_set_capability(from, "return-path", true);
+    migrate_set_capability(to, "return-path", true);
+
+    migrate_set_capability(from, "switchover-ack", true);
+    migrate_set_capability(to, "switchover-ack", true);
+
+    return NULL;
+}
+
+static void test_precopy_tcp_switchover_ack(void)
+{
+    MigrateCommon args = {
+        .listen_uri = "tcp:127.0.0.1:0",
+        .start_hook = test_migrate_switchover_ack_start,
+    };
+
+    test_precopy_common(&args);
+}
+
 #ifdef CONFIG_GNUTLS
 static void test_precopy_tcp_tls_psk_match(void)
 {
@@ -2695,6 +2717,10 @@ int main(int argc, char **argv)
 #endif /* CONFIG_GNUTLS */
 
     qtest_add_func("/migration/precopy/tcp/plain", test_precopy_tcp_plain);
+
+    qtest_add_func("/migration/precopy/tcp/plain/switchover-ack",
+                   test_precopy_tcp_switchover_ack);
+
 #ifdef CONFIG_GNUTLS
     qtest_add_func("/migration/precopy/tcp/tls/psk/match",
                    test_precopy_tcp_tls_psk_match);
-- 
2.26.3

[PATCH v4 5/9] vfio/migration: Refactor vfio_save_block() to return saved data size

[Avihai Horon]

Refactor vfio_save_block() to return the size of saved data on success
and -errno on error.

This will be used in next patch to implement VFIO migration pre-copy
support.

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
---
 hw/vfio/migration.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index 6b58dddb88..235978fd68 100644
--- a/hw/vfio/migration.c
+++ b/hw/vfio/migration.c
@@ -241,8 +241,8 @@ static int vfio_query_stop_copy_size(VFIODevice *vbasedev,
     return 0;
 }
 
-/* Returns 1 if end-of-stream is reached, 0 if more data and -errno if error */
-static int vfio_save_block(QEMUFile *f, VFIOMigration *migration)
+/* Returns the size of saved data on success and -errno on error */
+static ssize_t vfio_save_block(QEMUFile *f, VFIOMigration *migration)
 {
     ssize_t data_size;
 
@@ -252,7 +252,7 @@ static int vfio_save_block(QEMUFile *f, VFIOMigration *migration)
         return -errno;
     }
     if (data_size == 0) {
-        return 1;
+        return 0;
     }
 
     qemu_put_be64(f, VFIO_MIG_FLAG_DEV_DATA_STATE);
@@ -262,7 +262,7 @@ static int vfio_save_block(QEMUFile *f, VFIOMigration *migration)
 
     trace_vfio_save_block(migration->vbasedev->name, data_size);
 
-    return qemu_file_get_error(f);
+    return qemu_file_get_error(f) ?: data_size;
 }
 
 /* ---------------------------------------------------------------------- */
@@ -335,6 +335,7 @@ static void vfio_state_pending_exact(void *opaque, uint64_t *must_precopy,
 static int vfio_save_complete_precopy(QEMUFile *f, void *opaque)
 {
     VFIODevice *vbasedev = opaque;
+    ssize_t data_size;
     int ret;
 
     /* We reach here with device state STOP only */
@@ -345,11 +346,11 @@ static int vfio_save_complete_precopy(QEMUFile *f, void *opaque)
     }
 
     do {
-        ret = vfio_save_block(f, vbasedev->migration);
-        if (ret < 0) {
-            return ret;
+        data_size = vfio_save_block(f, vbasedev->migration);
+        if (data_size < 0) {
+            return data_size;
         }
-    } while (!ret);
+    } while (data_size);
 
     qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
     ret = qemu_file_get_error(f);
-- 
2.26.3

[PATCH v4 6/9] vfio/migration: Store VFIO migration flags in VFIOMigration

[Avihai Horon]

VFIO migration flags are queried once in vfio_migration_init(). Store
them in VFIOMigration so they can be used later to check the device's
migration capabilities without re-querying them.

This will be used in the next patch to check if the device supports
precopy migration.

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
---
 include/hw/vfio/vfio-common.h | 1 +
 hw/vfio/migration.c           | 1 +
 2 files changed, 2 insertions(+)

diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
index eed244f25f..5f29dab839 100644
--- a/include/hw/vfio/vfio-common.h
+++ b/include/hw/vfio/vfio-common.h
@@ -66,6 +66,7 @@ typedef struct VFIOMigration {
     int data_fd;
     void *data_buffer;
     size_t data_buffer_size;
+    uint64_t mig_flags;
 } VFIOMigration;
 
 typedef struct VFIOAddressSpace {
diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index 235978fd68..8d33414379 100644
--- a/hw/vfio/migration.c
+++ b/hw/vfio/migration.c
@@ -603,6 +603,7 @@ static int vfio_migration_init(VFIODevice *vbasedev)
     migration->vbasedev = vbasedev;
     migration->device_state = VFIO_DEVICE_STATE_RUNNING;
     migration->data_fd = -1;
+    migration->mig_flags = mig_flags;
 
     vbasedev->dirty_pages_supported = vfio_dma_logging_supported(vbasedev);
 
-- 
2.26.3

[PATCH v4 7/9] vfio/migration: Add VFIO migration pre-copy support

[Avihai Horon]

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>
---
 docs/devel/vfio-migration.rst |  35 +++++---
 include/hw/vfio/vfio-common.h |   2 +
 hw/vfio/common.c              |   6 +-
 hw/vfio/migration.c           | 165 ++++++++++++++++++++++++++++++++--
 hw/vfio/trace-events          |   4 +-
 5 files changed, 190 insertions(+), 22 deletions(-)

diff --git a/docs/devel/vfio-migration.rst b/docs/devel/vfio-migration.rst
index 1b68ccf115..e896b2a673 100644
--- a/docs/devel/vfio-migration.rst
+++ b/docs/devel/vfio-migration.rst
@@ -7,12 +7,14 @@ the guest is running on source host and restoring this saved state on the
 destination host. This document details how saving and restoring of VFIO
 devices is done in QEMU.
 
-Migration of VFIO devices currently consists of a single stop-and-copy phase.
-During the stop-and-copy phase the guest is stopped and the entire VFIO device
-data is transferred to the destination.
-
-The pre-copy phase of migration is currently not supported for VFIO devices.
-Support for VFIO pre-copy will be added later on.
+Migration of VFIO devices consists of two phases: the optional pre-copy phase,
+and the stop-and-copy phase. The pre-copy phase is iterative and allows to
+accommodate VFIO devices that have a large amount of data that needs to be
+transferred. The iterative pre-copy phase of migration allows for the guest to
+continue whilst the VFIO device state is transferred to the destination, this
+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.
 
 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
@@ -29,10 +31,20 @@ VFIO implements the device hooks for the iterative approach as follows:
 * A ``load_setup`` function that sets the VFIO device on the destination in
   _RESUMING state.
 
+* A ``state_pending_estimate`` function that reports an estimate of the
+  remaining pre-copy data that the vendor driver has yet to save for the VFIO
+  device.
+
 * A ``state_pending_exact`` function that reads pending_bytes from the vendor
   driver, which indicates the amount of data that the vendor driver has yet to
   save for the VFIO device.
 
+* An ``is_active_iterate`` function that indicates ``save_live_iterate`` is
+  active only when the VFIO device is in pre-copy states.
+
+* A ``save_live_iterate`` function that reads the VFIO device's data from the
+  vendor driver during iterative pre-copy phase.
+
 * 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
@@ -111,8 +123,10 @@ Flow of state changes during Live migration
 ===========================================
 
 Below is the flow of state change during live migration.
-The values in the brackets represent the VM state, the migration state, and
+The values in the parentheses represent the VM state, the migration state, and
 the VFIO device state, respectively.
+The text in the square brackets represents the flow if the VFIO device supports
+pre-copy.
 
 Live migration save path
 ------------------------
@@ -124,11 +138,12 @@ Live migration save path
                                   |
                      migrate_init spawns migration_thread
                 Migration thread then calls each device's .save_setup()
-                       (RUNNING, _SETUP, _RUNNING)
+                  (RUNNING, _SETUP, _RUNNING [_PRE_COPY])
                                   |
-                      (RUNNING, _ACTIVE, _RUNNING)
-             If device is active, get pending_bytes by .state_pending_exact()
+                  (RUNNING, _ACTIVE, _RUNNING [_PRE_COPY])
+      If device is active, get pending_bytes by .state_pending_{estimate,exact}()
           If total pending_bytes >= threshold_size, call .save_live_iterate()
+                  [Data of VFIO device for pre-copy phase is copied]
         Iterate till total pending bytes converge and are less than threshold
                                   |
   On migration completion, vCPU stops and calls .save_live_complete_precopy for
diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
index 5f29dab839..1db901c194 100644
--- a/include/hw/vfio/vfio-common.h
+++ b/include/hw/vfio/vfio-common.h
@@ -67,6 +67,8 @@ typedef struct VFIOMigration {
     void *data_buffer;
     size_t data_buffer_size;
     uint64_t mig_flags;
+    uint64_t precopy_init_size;
+    uint64_t precopy_dirty_size;
 } VFIOMigration;
 
 typedef struct VFIOAddressSpace {
diff --git a/hw/vfio/common.c b/hw/vfio/common.c
index 78358ede27..b73086e17a 100644
--- a/hw/vfio/common.c
+++ b/hw/vfio/common.c
@@ -492,7 +492,8 @@ static bool vfio_devices_all_dirty_tracking(VFIOContainer *container)
             }
 
             if (vbasedev->pre_copy_dirty_page_tracking == ON_OFF_AUTO_OFF &&
-                migration->device_state == VFIO_DEVICE_STATE_RUNNING) {
+                (migration->device_state == VFIO_DEVICE_STATE_RUNNING ||
+                 migration->device_state == VFIO_DEVICE_STATE_PRE_COPY)) {
                 return false;
             }
         }
@@ -537,7 +538,8 @@ static bool vfio_devices_all_running_and_mig_active(VFIOContainer *container)
                 return false;
             }
 
-            if (migration->device_state == VFIO_DEVICE_STATE_RUNNING) {
+            if (migration->device_state == VFIO_DEVICE_STATE_RUNNING ||
+                migration->device_state == VFIO_DEVICE_STATE_PRE_COPY) {
                 continue;
             } else {
                 return false;
diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index 8d33414379..d8f6a22ae1 100644
--- a/hw/vfio/migration.c
+++ b/hw/vfio/migration.c
@@ -68,6 +68,8 @@ static const char *mig_state_to_str(enum vfio_device_mig_state state)
         return "STOP_COPY";
     case VFIO_DEVICE_STATE_RESUMING:
         return "RESUMING";
+    case VFIO_DEVICE_STATE_PRE_COPY:
+        return "PRE_COPY";
     default:
         return "UNKNOWN STATE";
     }
@@ -241,6 +243,25 @@ static int vfio_query_stop_copy_size(VFIODevice *vbasedev,
     return 0;
 }
 
+static int vfio_query_precopy_size(VFIOMigration *migration)
+{
+    struct vfio_precopy_info precopy = {
+        .argsz = sizeof(precopy),
+    };
+
+    migration->precopy_init_size = 0;
+    migration->precopy_dirty_size = 0;
+
+    if (ioctl(migration->data_fd, VFIO_MIG_GET_PRECOPY_INFO, &precopy)) {
+        return -errno;
+    }
+
+    migration->precopy_init_size = precopy.initial_bytes;
+    migration->precopy_dirty_size = precopy.dirty_bytes;
+
+    return 0;
+}
+
 /* Returns the size of saved data on success and -errno on error */
 static ssize_t vfio_save_block(QEMUFile *f, VFIOMigration *migration)
 {
@@ -249,6 +270,14 @@ static ssize_t vfio_save_block(QEMUFile *f, VFIOMigration *migration)
     data_size = read(migration->data_fd, migration->data_buffer,
                      migration->data_buffer_size);
     if (data_size < 0) {
+        /*
+         * Pre-copy emptied all the device state for now. For more information,
+         * please refer to the Linux kernel VFIO uAPI.
+         */
+        if (errno == ENOMSG) {
+            return 0;
+        }
+
         return -errno;
     }
     if (data_size == 0) {
@@ -265,6 +294,38 @@ static ssize_t vfio_save_block(QEMUFile *f, VFIOMigration *migration)
     return qemu_file_get_error(f) ?: data_size;
 }
 
+static void vfio_update_estimated_pending_data(VFIOMigration *migration,
+                                               uint64_t data_size)
+{
+    if (!data_size) {
+        /*
+         * Pre-copy emptied all the device state for now, update estimated sizes
+         * accordingly.
+         */
+        migration->precopy_init_size = 0;
+        migration->precopy_dirty_size = 0;
+
+        return;
+    }
+
+    if (migration->precopy_init_size) {
+        uint64_t init_size = MIN(migration->precopy_init_size, data_size);
+
+        migration->precopy_init_size -= init_size;
+        data_size -= init_size;
+    }
+
+    migration->precopy_dirty_size -= MIN(migration->precopy_dirty_size,
+                                         data_size);
+}
+
+static bool vfio_precopy_supported(VFIODevice *vbasedev)
+{
+    VFIOMigration *migration = vbasedev->migration;
+
+    return migration->mig_flags & VFIO_MIGRATION_PRE_COPY;
+}
+
 /* ---------------------------------------------------------------------- */
 
 static int vfio_save_setup(QEMUFile *f, void *opaque)
@@ -285,6 +346,28 @@ static int vfio_save_setup(QEMUFile *f, void *opaque)
         return -ENOMEM;
     }
 
+    if (vfio_precopy_supported(vbasedev)) {
+        int ret;
+
+        switch (migration->device_state) {
+        case VFIO_DEVICE_STATE_RUNNING:
+            ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_PRE_COPY,
+                                           VFIO_DEVICE_STATE_RUNNING);
+            if (ret) {
+                return ret;
+            }
+
+            vfio_query_precopy_size(migration);
+
+            break;
+        case VFIO_DEVICE_STATE_STOP:
+            /* vfio_save_complete_precopy() will go to STOP_COPY */
+            break;
+        default:
+            return -EINVAL;
+        }
+    }
+
     trace_vfio_save_setup(vbasedev->name, migration->data_buffer_size);
 
     qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
@@ -299,26 +382,42 @@ static void vfio_save_cleanup(void *opaque)
 
     g_free(migration->data_buffer);
     migration->data_buffer = NULL;
+    migration->precopy_init_size = 0;
+    migration->precopy_dirty_size = 0;
     vfio_migration_cleanup(vbasedev);
     trace_vfio_save_cleanup(vbasedev->name);
 }
 
+static void vfio_state_pending_estimate(void *opaque, uint64_t *must_precopy,
+                                        uint64_t *can_postcopy)
+{
+    VFIODevice *vbasedev = opaque;
+    VFIOMigration *migration = vbasedev->migration;
+
+    if (migration->device_state != VFIO_DEVICE_STATE_PRE_COPY) {
+        return;
+    }
+
+    *must_precopy +=
+        migration->precopy_init_size + migration->precopy_dirty_size;
+
+    trace_vfio_state_pending_estimate(vbasedev->name, *must_precopy,
+                                      *can_postcopy,
+                                      migration->precopy_init_size,
+                                      migration->precopy_dirty_size);
+}
+
 /*
  * Migration size of VFIO devices can be as little as a few KBs or as big as
  * many GBs. This value should be big enough to cover the worst case.
  */
 #define VFIO_MIG_STOP_COPY_SIZE (100 * GiB)
 
-/*
- * Only exact function is implemented and not estimate function. The reason is
- * that during pre-copy phase of migration the estimate function is called
- * repeatedly while pending RAM size is over the threshold, thus migration
- * can't converge and querying the VFIO device pending data size is useless.
- */
 static void vfio_state_pending_exact(void *opaque, uint64_t *must_precopy,
                                      uint64_t *can_postcopy)
 {
     VFIODevice *vbasedev = opaque;
+    VFIOMigration *migration = vbasedev->migration;
     uint64_t stop_copy_size = VFIO_MIG_STOP_COPY_SIZE;
 
     /*
@@ -328,8 +427,48 @@ static void vfio_state_pending_exact(void *opaque, uint64_t *must_precopy,
     vfio_query_stop_copy_size(vbasedev, &stop_copy_size);
     *must_precopy += stop_copy_size;
 
+    if (migration->device_state == VFIO_DEVICE_STATE_PRE_COPY) {
+        vfio_query_precopy_size(migration);
+
+        *must_precopy +=
+            migration->precopy_init_size + migration->precopy_dirty_size;
+    }
+
     trace_vfio_state_pending_exact(vbasedev->name, *must_precopy, *can_postcopy,
-                                   stop_copy_size);
+                                   stop_copy_size, migration->precopy_init_size,
+                                   migration->precopy_dirty_size);
+}
+
+static bool vfio_is_active_iterate(void *opaque)
+{
+    VFIODevice *vbasedev = opaque;
+    VFIOMigration *migration = vbasedev->migration;
+
+    return migration->device_state == VFIO_DEVICE_STATE_PRE_COPY;
+}
+
+static int vfio_save_iterate(QEMUFile *f, void *opaque)
+{
+    VFIODevice *vbasedev = opaque;
+    VFIOMigration *migration = vbasedev->migration;
+    ssize_t data_size;
+
+    data_size = vfio_save_block(f, migration);
+    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);
+
+    trace_vfio_save_iterate(vbasedev->name, migration->precopy_init_size,
+                            migration->precopy_dirty_size);
+
+    /*
+     * A VFIO device's pre-copy dirty_bytes is not guaranteed to reach zero.
+     * Return 1 so following handlers will not be potentially blocked.
+     */
+    return 1;
 }
 
 static int vfio_save_complete_precopy(QEMUFile *f, void *opaque)
@@ -338,7 +477,7 @@ static int vfio_save_complete_precopy(QEMUFile *f, void *opaque)
     ssize_t data_size;
     int ret;
 
-    /* We reach here with device state STOP only */
+    /* We reach here with device state STOP or STOP_COPY only */
     ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_STOP_COPY,
                                    VFIO_DEVICE_STATE_STOP);
     if (ret) {
@@ -457,7 +596,10 @@ static int vfio_load_state(QEMUFile *f, void *opaque, int version_id)
 static const SaveVMHandlers savevm_vfio_handlers = {
     .save_setup = vfio_save_setup,
     .save_cleanup = vfio_save_cleanup,
+    .state_pending_estimate = vfio_state_pending_estimate,
     .state_pending_exact = vfio_state_pending_exact,
+    .is_active_iterate = vfio_is_active_iterate,
+    .save_live_iterate = vfio_save_iterate,
     .save_live_complete_precopy = vfio_save_complete_precopy,
     .save_state = vfio_save_state,
     .load_setup = vfio_load_setup,
@@ -470,13 +612,18 @@ static const SaveVMHandlers savevm_vfio_handlers = {
 static void vfio_vmstate_change(void *opaque, bool running, RunState state)
 {
     VFIODevice *vbasedev = opaque;
+    VFIOMigration *migration = vbasedev->migration;
     enum vfio_device_mig_state new_state;
     int ret;
 
     if (running) {
         new_state = VFIO_DEVICE_STATE_RUNNING;
     } else {
-        new_state = VFIO_DEVICE_STATE_STOP;
+        new_state =
+            (migration->device_state == VFIO_DEVICE_STATE_PRE_COPY &&
+             (state == RUN_STATE_FINISH_MIGRATE || state == RUN_STATE_PAUSED)) ?
+                VFIO_DEVICE_STATE_STOP_COPY :
+                VFIO_DEVICE_STATE_STOP;
     }
 
     /*
diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
index 646e42fd27..548f9488a7 100644
--- a/hw/vfio/trace-events
+++ b/hw/vfio/trace-events
@@ -162,6 +162,8 @@ vfio_save_block(const char *name, int data_size) " (%s) data_size %d"
 vfio_save_cleanup(const char *name) " (%s)"
 vfio_save_complete_precopy(const char *name, int ret) " (%s) ret %d"
 vfio_save_device_config_state(const char *name) " (%s)"
+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"
 vfio_save_setup(const char *name, uint64_t data_buffer_size) " (%s) data buffer size 0x%"PRIx64
-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
+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
+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
 vfio_vmstate_change(const char *name, int running, const char *reason, const char *dev_state) " (%s) running %d reason %s device state %s"
-- 
2.26.3

[PATCH v4 8/9] vfio/migration: Add x-allow-pre-copy VFIO device property

[Avihai Horon]

Add a new VFIO device property x-allow-pre-copy to keep migration
compatibility to/from older QEMU versions that don't have VFIO pre-copy
support.

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
---
 include/hw/vfio/vfio-common.h | 1 +
 hw/core/machine.c             | 1 +
 hw/vfio/migration.c           | 3 ++-
 hw/vfio/pci.c                 | 2 ++
 4 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
index 1db901c194..a53ecbe2e0 100644
--- a/include/hw/vfio/vfio-common.h
+++ b/include/hw/vfio/vfio-common.h
@@ -146,6 +146,7 @@ typedef struct VFIODevice {
     VFIOMigration *migration;
     Error *migration_blocker;
     OnOffAuto pre_copy_dirty_page_tracking;
+    bool allow_pre_copy;
     bool dirty_pages_supported;
     bool dirty_tracking;
 } VFIODevice;
diff --git a/hw/core/machine.c b/hw/core/machine.c
index 1000406211..64ac3fe38e 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -41,6 +41,7 @@
 
 GlobalProperty hw_compat_8_0[] = {
     { "migration", "multifd-flush-after-each-section", "on"},
+    { "vfio-pci", "x-allow-pre-copy", "false" },
 };
 const size_t hw_compat_8_0_len = G_N_ELEMENTS(hw_compat_8_0);
 
diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index d8f6a22ae1..cb6923ed3f 100644
--- a/hw/vfio/migration.c
+++ b/hw/vfio/migration.c
@@ -323,7 +323,8 @@ static bool vfio_precopy_supported(VFIODevice *vbasedev)
 {
     VFIOMigration *migration = vbasedev->migration;
 
-    return migration->mig_flags & VFIO_MIGRATION_PRE_COPY;
+    return vbasedev->allow_pre_copy &&
+           migration->mig_flags & VFIO_MIGRATION_PRE_COPY;
 }
 
 /* ---------------------------------------------------------------------- */
diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index 73874a94de..c69813af7f 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -3335,6 +3335,8 @@ static Property vfio_pci_dev_properties[] = {
     DEFINE_PROP_ON_OFF_AUTO("x-pre-copy-dirty-page-tracking", VFIOPCIDevice,
                             vbasedev.pre_copy_dirty_page_tracking,
                             ON_OFF_AUTO_ON),
+    DEFINE_PROP_BOOL("x-allow-pre-copy", VFIOPCIDevice,
+                     vbasedev.allow_pre_copy, true),
     DEFINE_PROP_ON_OFF_AUTO("display", VFIOPCIDevice,
                             display, ON_OFF_AUTO_OFF),
     DEFINE_PROP_UINT32("xres", VFIOPCIDevice, display_xres, 0),
-- 
2.26.3

[PATCH v4 9/9] vfio/migration: Add support for switchover ack capability

[Avihai Horon]

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.

As precopy support and precopy initial bytes support come together in
VFIO migration, use x-allow-pre-copy device property to control usage of
this feature as well.

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
---
 docs/devel/vfio-migration.rst | 10 ++++++++
 include/hw/vfio/vfio-common.h |  2 ++
 hw/vfio/migration.c           | 48 ++++++++++++++++++++++++++++++++++-
 3 files changed, 59 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/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
index a53ecbe2e0..ad0562c8b7 100644
--- a/include/hw/vfio/vfio-common.h
+++ b/include/hw/vfio/vfio-common.h
@@ -69,6 +69,8 @@ typedef struct VFIOMigration {
     uint64_t mig_flags;
     uint64_t precopy_init_size;
     uint64_t precopy_dirty_size;
+    bool switchover_ack_needed;
+    bool initial_data_sent;
 } VFIOMigration;
 
 typedef struct VFIOAddressSpace {
diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index cb6923ed3f..ede29ffb5c 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
@@ -218,6 +221,7 @@ static void vfio_migration_cleanup(VFIODevice *vbasedev)
 
     close(migration->data_fd);
     migration->data_fd = -1;
+    migration->switchover_ack_needed = false;
 }
 
 static int vfio_query_stop_copy_size(VFIODevice *vbasedev,
@@ -350,6 +354,10 @@ static int vfio_save_setup(QEMUFile *f, void *opaque)
     if (vfio_precopy_supported(vbasedev)) {
         int ret;
 
+        if (migrate_switchover_ack()) {
+            migration->switchover_ack_needed = true;
+        }
+
         switch (migration->device_state) {
         case VFIO_DEVICE_STATE_RUNNING:
             ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_PRE_COPY,
@@ -385,6 +393,7 @@ 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);
 }
@@ -458,10 +467,17 @@ 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 (migration->switchover_ack_needed && !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);
 
@@ -526,6 +542,10 @@ static int vfio_load_setup(QEMUFile *f, void *opaque)
 {
     VFIODevice *vbasedev = opaque;
 
+    if (migrate_switchover_ack() && vfio_precopy_supported(vbasedev)) {
+        vbasedev->migration->switchover_ack_needed = true;
+    }
+
     return vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_RESUMING,
                                    vbasedev->migration->device_state);
 }
@@ -580,6 +600,23 @@ static int vfio_load_state(QEMUFile *f, void *opaque, int version_id)
             }
             break;
         }
+        case VFIO_MIG_FLAG_DEV_INIT_DATA_SENT:
+        {
+            if (!vbasedev->migration->switchover_ack_needed) {
+                error_report("%s: Received INIT_DATA_SENT but switchover ack "
+                             "is not needed", 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;
@@ -594,6 +631,14 @@ 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;
+    VFIOMigration *migration = vbasedev->migration;
+
+    return migration->switchover_ack_needed;
+}
+
 static const SaveVMHandlers savevm_vfio_handlers = {
     .save_setup = vfio_save_setup,
     .save_cleanup = vfio_save_cleanup,
@@ -606,6 +651,7 @@ 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,
 };
 
 /* ---------------------------------------------------------------------- */
-- 
2.26.3

Re: [PATCH v4 2/9] migration: Implement switchover ack logic

[Peter Xu]

On Sun, May 28, 2023 at 05:06:45PM +0300, Avihai Horon wrote:
> Implement switchover ack logic. This prevents the source from stopping
> the VM and completing the migration until an ACK is received from the
> destination that it's OK to do so.
> 
> To achieve this, a new SaveVMHandlers handler switchover_ack_needed()
> and a new return path message MIG_RP_MSG_SWITCHOVER_ACK are added.
> 
> The switchover_ack_needed() handler is called during migration setup in
> the destination to check if switchover ack is used by the migrated
> device.
> 
> When switchover is approved by all migrated devices in the destination
> that support this capability, the MIG_RP_MSG_SWITCHOVER_ACK return path
> message is sent to the source to notify it that it's OK to do
> switchover.
> 
> Signed-off-by: Avihai Horon <avihaih@nvidia.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

-- 
Peter Xu

Re: [PATCH v4 6/9] vfio/migration: Store VFIO migration flags in VFIOMigration

[Cédric Le Goater]

On 5/28/23 16:06, Avihai Horon wrote:
> VFIO migration flags are queried once in vfio_migration_init(). Store
> them in VFIOMigration so they can be used later to check the device's
> migration capabilities without re-querying them.
> 
> This will be used in the next patch to check if the device supports
> precopy migration.
> 
> Signed-off-by: Avihai Horon <avihaih@nvidia.com>

Reviewed-by: Cédric Le Goater <clg@redhat.com>

Thanks,

C.

> ---
>   include/hw/vfio/vfio-common.h | 1 +
>   hw/vfio/migration.c           | 1 +
>   2 files changed, 2 insertions(+)
> 
> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> index eed244f25f..5f29dab839 100644
> --- a/include/hw/vfio/vfio-common.h
> +++ b/include/hw/vfio/vfio-common.h
> @@ -66,6 +66,7 @@ typedef struct VFIOMigration {
>       int data_fd;
>       void *data_buffer;
>       size_t data_buffer_size;
> +    uint64_t mig_flags;
>   } VFIOMigration;
>   
>   typedef struct VFIOAddressSpace {
> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> index 235978fd68..8d33414379 100644
> --- a/hw/vfio/migration.c
> +++ b/hw/vfio/migration.c
> @@ -603,6 +603,7 @@ static int vfio_migration_init(VFIODevice *vbasedev)
>       migration->vbasedev = vbasedev;
>       migration->device_state = VFIO_DEVICE_STATE_RUNNING;
>       migration->data_fd = -1;
> +    migration->mig_flags = mig_flags;
>   
>       vbasedev->dirty_pages_supported = vfio_dma_logging_supported(vbasedev);
>   

Re: [PATCH v4 8/9] vfio/migration: Add x-allow-pre-copy VFIO device property

[Cédric Le Goater]

On 5/28/23 16:06, Avihai Horon wrote:
> Add a new VFIO device property x-allow-pre-copy to keep migration
> compatibility to/from older QEMU versions that don't have VFIO pre-copy
> support.
> 
> Signed-off-by: Avihai Horon <avihaih@nvidia.com>


Reviewed-by: Cédric Le Goater <clg@redhat.com>

Thanks,

C.

> ---
>   include/hw/vfio/vfio-common.h | 1 +
>   hw/core/machine.c             | 1 +
>   hw/vfio/migration.c           | 3 ++-
>   hw/vfio/pci.c                 | 2 ++
>   4 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> index 1db901c194..a53ecbe2e0 100644
> --- a/include/hw/vfio/vfio-common.h
> +++ b/include/hw/vfio/vfio-common.h
> @@ -146,6 +146,7 @@ typedef struct VFIODevice {
>       VFIOMigration *migration;
>       Error *migration_blocker;
>       OnOffAuto pre_copy_dirty_page_tracking;
> +    bool allow_pre_copy;
>       bool dirty_pages_supported;
>       bool dirty_tracking;
>   } VFIODevice;
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index 1000406211..64ac3fe38e 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -41,6 +41,7 @@
>   
>   GlobalProperty hw_compat_8_0[] = {
>       { "migration", "multifd-flush-after-each-section", "on"},
> +    { "vfio-pci", "x-allow-pre-copy", "false" },
>   };
>   const size_t hw_compat_8_0_len = G_N_ELEMENTS(hw_compat_8_0);
>   
> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> index d8f6a22ae1..cb6923ed3f 100644
> --- a/hw/vfio/migration.c
> +++ b/hw/vfio/migration.c
> @@ -323,7 +323,8 @@ static bool vfio_precopy_supported(VFIODevice *vbasedev)
>   {
>       VFIOMigration *migration = vbasedev->migration;
>   
> -    return migration->mig_flags & VFIO_MIGRATION_PRE_COPY;
> +    return vbasedev->allow_pre_copy &&
> +           migration->mig_flags & VFIO_MIGRATION_PRE_COPY;
>   }
>   
>   /* ---------------------------------------------------------------------- */
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index 73874a94de..c69813af7f 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -3335,6 +3335,8 @@ static Property vfio_pci_dev_properties[] = {
>       DEFINE_PROP_ON_OFF_AUTO("x-pre-copy-dirty-page-tracking", VFIOPCIDevice,
>                               vbasedev.pre_copy_dirty_page_tracking,
>                               ON_OFF_AUTO_ON),
> +    DEFINE_PROP_BOOL("x-allow-pre-copy", VFIOPCIDevice,
> +                     vbasedev.allow_pre_copy, true),
>       DEFINE_PROP_ON_OFF_AUTO("display", VFIOPCIDevice,
>                               display, ON_OFF_AUTO_OFF),
>       DEFINE_PROP_UINT32("xres", VFIOPCIDevice, display_xres, 0),

Re: [PATCH v4 7/9] vfio/migration: Add VFIO migration pre-copy support

[Cédric Le Goater]

On 5/28/23 16:06, Avihai Horon wrote:
> 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>

LGTM,
  
Reviewed-by: Cédric Le Goater <clg@redhat.com>

one minor issue below,

> ---
>   docs/devel/vfio-migration.rst |  35 +++++---
>   include/hw/vfio/vfio-common.h |   2 +
>   hw/vfio/common.c              |   6 +-
>   hw/vfio/migration.c           | 165 ++++++++++++++++++++++++++++++++--
>   hw/vfio/trace-events          |   4 +-
>   5 files changed, 190 insertions(+), 22 deletions(-)
> 
> diff --git a/docs/devel/vfio-migration.rst b/docs/devel/vfio-migration.rst
> index 1b68ccf115..e896b2a673 100644
> --- a/docs/devel/vfio-migration.rst
> +++ b/docs/devel/vfio-migration.rst
> @@ -7,12 +7,14 @@ the guest is running on source host and restoring this saved state on the
>   destination host. This document details how saving and restoring of VFIO
>   devices is done in QEMU.
>   
> -Migration of VFIO devices currently consists of a single stop-and-copy phase.
> -During the stop-and-copy phase the guest is stopped and the entire VFIO device
> -data is transferred to the destination.
> -
> -The pre-copy phase of migration is currently not supported for VFIO devices.
> -Support for VFIO pre-copy will be added later on.
> +Migration of VFIO devices consists of two phases: the optional pre-copy phase,
> +and the stop-and-copy phase. The pre-copy phase is iterative and allows to
> +accommodate VFIO devices that have a large amount of data that needs to be
> +transferred. The iterative pre-copy phase of migration allows for the guest to
> +continue whilst the VFIO device state is transferred to the destination, this
> +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.
>   
>   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
> @@ -29,10 +31,20 @@ VFIO implements the device hooks for the iterative approach as follows:
>   * A ``load_setup`` function that sets the VFIO device on the destination in
>     _RESUMING state.
>   
> +* A ``state_pending_estimate`` function that reports an estimate of the
> +  remaining pre-copy data that the vendor driver has yet to save for the VFIO
> +  device.
> +
>   * A ``state_pending_exact`` function that reads pending_bytes from the vendor
>     driver, which indicates the amount of data that the vendor driver has yet to
>     save for the VFIO device.
>   
> +* An ``is_active_iterate`` function that indicates ``save_live_iterate`` is
> +  active only when the VFIO device is in pre-copy states.
> +
> +* A ``save_live_iterate`` function that reads the VFIO device's data from the
> +  vendor driver during iterative pre-copy phase.
> +
>   * 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
> @@ -111,8 +123,10 @@ Flow of state changes during Live migration
>   ===========================================
>   
>   Below is the flow of state change during live migration.
> -The values in the brackets represent the VM state, the migration state, and
> +The values in the parentheses represent the VM state, the migration state, and
>   the VFIO device state, respectively.
> +The text in the square brackets represents the flow if the VFIO device supports
> +pre-copy.
>   
>   Live migration save path
>   ------------------------
> @@ -124,11 +138,12 @@ Live migration save path
>                                     |
>                        migrate_init spawns migration_thread
>                   Migration thread then calls each device's .save_setup()
> -                       (RUNNING, _SETUP, _RUNNING)
> +                  (RUNNING, _SETUP, _RUNNING [_PRE_COPY])
>                                     |
> -                      (RUNNING, _ACTIVE, _RUNNING)
> -             If device is active, get pending_bytes by .state_pending_exact()
> +                  (RUNNING, _ACTIVE, _RUNNING [_PRE_COPY])
> +      If device is active, get pending_bytes by .state_pending_{estimate,exact}()
>             If total pending_bytes >= threshold_size, call .save_live_iterate()
> +                  [Data of VFIO device for pre-copy phase is copied]
>           Iterate till total pending bytes converge and are less than threshold
>                                     |
>     On migration completion, vCPU stops and calls .save_live_complete_precopy for
> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> index 5f29dab839..1db901c194 100644
> --- a/include/hw/vfio/vfio-common.h
> +++ b/include/hw/vfio/vfio-common.h
> @@ -67,6 +67,8 @@ typedef struct VFIOMigration {
>       void *data_buffer;
>       size_t data_buffer_size;
>       uint64_t mig_flags;
> +    uint64_t precopy_init_size;
> +    uint64_t precopy_dirty_size;
>   } VFIOMigration;
>   
>   typedef struct VFIOAddressSpace {
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 78358ede27..b73086e17a 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -492,7 +492,8 @@ static bool vfio_devices_all_dirty_tracking(VFIOContainer *container)
>               }
>   
>               if (vbasedev->pre_copy_dirty_page_tracking == ON_OFF_AUTO_OFF &&
> -                migration->device_state == VFIO_DEVICE_STATE_RUNNING) {
> +                (migration->device_state == VFIO_DEVICE_STATE_RUNNING ||
> +                 migration->device_state == VFIO_DEVICE_STATE_PRE_COPY)) {
>                   return false;
>               }
>           }
> @@ -537,7 +538,8 @@ static bool vfio_devices_all_running_and_mig_active(VFIOContainer *container)
>                   return false;
>               }
>   
> -            if (migration->device_state == VFIO_DEVICE_STATE_RUNNING) {
> +            if (migration->device_state == VFIO_DEVICE_STATE_RUNNING ||
> +                migration->device_state == VFIO_DEVICE_STATE_PRE_COPY) {
>                   continue;
>               } else {
>                   return false;
> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> index 8d33414379..d8f6a22ae1 100644
> --- a/hw/vfio/migration.c
> +++ b/hw/vfio/migration.c
> @@ -68,6 +68,8 @@ static const char *mig_state_to_str(enum vfio_device_mig_state state)
>           return "STOP_COPY";
>       case VFIO_DEVICE_STATE_RESUMING:
>           return "RESUMING";
> +    case VFIO_DEVICE_STATE_PRE_COPY:
> +        return "PRE_COPY";
>       default:
>           return "UNKNOWN STATE";
>       }
> @@ -241,6 +243,25 @@ static int vfio_query_stop_copy_size(VFIODevice *vbasedev,
>       return 0;
>   }
>   
> +static int vfio_query_precopy_size(VFIOMigration *migration)
> +{
> +    struct vfio_precopy_info precopy = {
> +        .argsz = sizeof(precopy),
> +    };
> +
> +    migration->precopy_init_size = 0;
> +    migration->precopy_dirty_size = 0;
> +
> +    if (ioctl(migration->data_fd, VFIO_MIG_GET_PRECOPY_INFO, &precopy)) {
> +        return -errno;
> +    }
> +
> +    migration->precopy_init_size = precopy.initial_bytes;
> +    migration->precopy_dirty_size = precopy.dirty_bytes;
> +
> +    return 0;
> +}
> +
>   /* Returns the size of saved data on success and -errno on error */
>   static ssize_t vfio_save_block(QEMUFile *f, VFIOMigration *migration)
>   {
> @@ -249,6 +270,14 @@ static ssize_t vfio_save_block(QEMUFile *f, VFIOMigration *migration)
>       data_size = read(migration->data_fd, migration->data_buffer,
>                        migration->data_buffer_size);
>       if (data_size < 0) {
> +        /*
> +         * Pre-copy emptied all the device state for now. For more information,
> +         * please refer to the Linux kernel VFIO uAPI.
> +         */
> +        if (errno == ENOMSG) {
> +            return 0;
> +        }
> +
>           return -errno;
>       }
>       if (data_size == 0) {
> @@ -265,6 +294,38 @@ static ssize_t vfio_save_block(QEMUFile *f, VFIOMigration *migration)
>       return qemu_file_get_error(f) ?: data_size;
>   }
>   
> +static void vfio_update_estimated_pending_data(VFIOMigration *migration,
> +                                               uint64_t data_size)
> +{
> +    if (!data_size) {
> +        /*
> +         * Pre-copy emptied all the device state for now, update estimated sizes
> +         * accordingly.
> +         */
> +        migration->precopy_init_size = 0;
> +        migration->precopy_dirty_size = 0;
> +
> +        return;
> +    }
> +
> +    if (migration->precopy_init_size) {
> +        uint64_t init_size = MIN(migration->precopy_init_size, data_size);
> +
> +        migration->precopy_init_size -= init_size;
> +        data_size -= init_size;
> +    }
> +
> +    migration->precopy_dirty_size -= MIN(migration->precopy_dirty_size,
> +                                         data_size);
> +}
> +
> +static bool vfio_precopy_supported(VFIODevice *vbasedev)
> +{
> +    VFIOMigration *migration = vbasedev->migration;
> +
> +    return migration->mig_flags & VFIO_MIGRATION_PRE_COPY;
> +}
> +
>   /* ---------------------------------------------------------------------- */
>   
>   static int vfio_save_setup(QEMUFile *f, void *opaque)
> @@ -285,6 +346,28 @@ static int vfio_save_setup(QEMUFile *f, void *opaque)
>           return -ENOMEM;
>       }
>   
> +    if (vfio_precopy_supported(vbasedev)) {
> +        int ret;
> +
> +        switch (migration->device_state) {
> +        case VFIO_DEVICE_STATE_RUNNING:
> +            ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_PRE_COPY,
> +                                           VFIO_DEVICE_STATE_RUNNING);
> +            if (ret) {
> +                return ret;
> +            }
> +
> +            vfio_query_precopy_size(migration);
> +
> +            break;
> +        case VFIO_DEVICE_STATE_STOP:
> +            /* vfio_save_complete_precopy() will go to STOP_COPY */
> +            break;
> +        default:
> +            return -EINVAL;
> +        }
> +    }
> +
>       trace_vfio_save_setup(vbasedev->name, migration->data_buffer_size);
>   
>       qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
> @@ -299,26 +382,42 @@ static void vfio_save_cleanup(void *opaque)
>   
>       g_free(migration->data_buffer);
>       migration->data_buffer = NULL;
> +    migration->precopy_init_size = 0;
> +    migration->precopy_dirty_size = 0;
>       vfio_migration_cleanup(vbasedev);
>       trace_vfio_save_cleanup(vbasedev->name);
>   }
>   
> +static void vfio_state_pending_estimate(void *opaque, uint64_t *must_precopy,
> +                                        uint64_t *can_postcopy)
> +{
> +    VFIODevice *vbasedev = opaque;
> +    VFIOMigration *migration = vbasedev->migration;
> +
> +    if (migration->device_state != VFIO_DEVICE_STATE_PRE_COPY) {
> +        return;
> +    }
> +
> +    *must_precopy +=
> +        migration->precopy_init_size + migration->precopy_dirty_size;
> +
> +    trace_vfio_state_pending_estimate(vbasedev->name, *must_precopy,
> +                                      *can_postcopy,
> +                                      migration->precopy_init_size,
> +                                      migration->precopy_dirty_size);
> +}
> +
>   /*
>    * Migration size of VFIO devices can be as little as a few KBs or as big as
>    * many GBs. This value should be big enough to cover the worst case.
>    */
>   #define VFIO_MIG_STOP_COPY_SIZE (100 * GiB)
>   
> -/*
> - * Only exact function is implemented and not estimate function. The reason is
> - * that during pre-copy phase of migration the estimate function is called
> - * repeatedly while pending RAM size is over the threshold, thus migration
> - * can't converge and querying the VFIO device pending data size is useless.
> - */
>   static void vfio_state_pending_exact(void *opaque, uint64_t *must_precopy,
>                                        uint64_t *can_postcopy)
>   {
>       VFIODevice *vbasedev = opaque;
> +    VFIOMigration *migration = vbasedev->migration;
>       uint64_t stop_copy_size = VFIO_MIG_STOP_COPY_SIZE;
>   
>       /*
> @@ -328,8 +427,48 @@ static void vfio_state_pending_exact(void *opaque, uint64_t *must_precopy,
>       vfio_query_stop_copy_size(vbasedev, &stop_copy_size);
>       *must_precopy += stop_copy_size;
>   
> +    if (migration->device_state == VFIO_DEVICE_STATE_PRE_COPY) {
> +        vfio_query_precopy_size(migration);
> +
> +        *must_precopy +=
> +            migration->precopy_init_size + migration->precopy_dirty_size;
> +    }
> +
>       trace_vfio_state_pending_exact(vbasedev->name, *must_precopy, *can_postcopy,
> -                                   stop_copy_size);
> +                                   stop_copy_size, migration->precopy_init_size,
> +                                   migration->precopy_dirty_size);
> +}
> +
> +static bool vfio_is_active_iterate(void *opaque)
> +{
> +    VFIODevice *vbasedev = opaque;
> +    VFIOMigration *migration = vbasedev->migration;
> +
> +    return migration->device_state == VFIO_DEVICE_STATE_PRE_COPY;
> +}
> +
> +static int vfio_save_iterate(QEMUFile *f, void *opaque)
> +{
> +    VFIODevice *vbasedev = opaque;
> +    VFIOMigration *migration = vbasedev->migration;
> +    ssize_t data_size;
> +
> +    data_size = vfio_save_block(f, migration);
> +    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);
> +
> +    trace_vfio_save_iterate(vbasedev->name, migration->precopy_init_size,
> +                            migration->precopy_dirty_size);
> +
> +    /*
> +     * A VFIO device's pre-copy dirty_bytes is not guaranteed to reach zero.
> +     * Return 1 so following handlers will not be potentially blocked.
> +     */
> +    return 1;
>   }
>   
>   static int vfio_save_complete_precopy(QEMUFile *f, void *opaque)
> @@ -338,7 +477,7 @@ static int vfio_save_complete_precopy(QEMUFile *f, void *opaque)
>       ssize_t data_size;
>       int ret;
>   
> -    /* We reach here with device state STOP only */
> +    /* We reach here with device state STOP or STOP_COPY only */
>       ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_STOP_COPY,
>                                      VFIO_DEVICE_STATE_STOP);
>       if (ret) {
> @@ -457,7 +596,10 @@ static int vfio_load_state(QEMUFile *f, void *opaque, int version_id)
>   static const SaveVMHandlers savevm_vfio_handlers = {
>       .save_setup = vfio_save_setup,
>       .save_cleanup = vfio_save_cleanup,
> +    .state_pending_estimate = vfio_state_pending_estimate,
>       .state_pending_exact = vfio_state_pending_exact,
> +    .is_active_iterate = vfio_is_active_iterate,
> +    .save_live_iterate = vfio_save_iterate,
>       .save_live_complete_precopy = vfio_save_complete_precopy,
>       .save_state = vfio_save_state,
>       .load_setup = vfio_load_setup,
> @@ -470,13 +612,18 @@ static const SaveVMHandlers savevm_vfio_handlers = {
>   static void vfio_vmstate_change(void *opaque, bool running, RunState state)
>   {
>       VFIODevice *vbasedev = opaque;
> +    VFIOMigration *migration = vbasedev->migration;
>       enum vfio_device_mig_state new_state;
>       int ret;
>   
>       if (running) {
>           new_state = VFIO_DEVICE_STATE_RUNNING;
>       } else {
> -        new_state = VFIO_DEVICE_STATE_STOP;
> +        new_state =
> +            (migration->device_state == VFIO_DEVICE_STATE_PRE_COPY &&
> +             (state == RUN_STATE_FINISH_MIGRATE || state == RUN_STATE_PAUSED)) ?
> +                VFIO_DEVICE_STATE_STOP_COPY :
> +                VFIO_DEVICE_STATE_STOP;
>       }
>   
>       /*
> diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
> index 646e42fd27..548f9488a7 100644
> --- a/hw/vfio/trace-events
> +++ b/hw/vfio/trace-events
> @@ -162,6 +162,8 @@ vfio_save_block(const char *name, int data_size) " (%s) data_size %d"
>   vfio_save_cleanup(const char *name) " (%s)"
>   vfio_save_complete_precopy(const char *name, int ret) " (%s) ret %d"
>   vfio_save_device_config_state(const char *name) " (%s)"
> +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"

the extra '"' at the end breaks compile. No need to resend just for that.
It can be fixed.

Thanks,

C.

>   vfio_save_setup(const char *name, uint64_t data_buffer_size) " (%s) data buffer size 0x%"PRIx64
> -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
> +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
> +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
>   vfio_vmstate_change(const char *name, int running, const char *reason, const char *dev_state) " (%s) running %d reason %s device state %s"

Re: [PATCH v4 7/9] vfio/migration: Add VFIO migration pre-copy support

[Avihai Horon]

On 30/05/2023 12:28, Cédric Le Goater wrote:
> External email: Use caution opening links or attachments
>
>
> On 5/28/23 16:06, Avihai Horon wrote:
>> 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>
>
> LGTM,
>
> Reviewed-by: Cédric Le Goater <clg@redhat.com>
>
> one minor issue below,
>
>> ---
>>   docs/devel/vfio-migration.rst |  35 +++++---
>>   include/hw/vfio/vfio-common.h |   2 +
>>   hw/vfio/common.c              |   6 +-
>>   hw/vfio/migration.c           | 165 ++++++++++++++++++++++++++++++++--
>>   hw/vfio/trace-events          |   4 +-
>>   5 files changed, 190 insertions(+), 22 deletions(-)
>>
>> diff --git a/docs/devel/vfio-migration.rst 
>> b/docs/devel/vfio-migration.rst
>> index 1b68ccf115..e896b2a673 100644
>> --- a/docs/devel/vfio-migration.rst
>> +++ b/docs/devel/vfio-migration.rst
>> @@ -7,12 +7,14 @@ the guest is running on source host and restoring 
>> this saved state on the
>>   destination host. This document details how saving and restoring of 
>> VFIO
>>   devices is done in QEMU.
>>
>> -Migration of VFIO devices currently consists of a single 
>> stop-and-copy phase.
>> -During the stop-and-copy phase the guest is stopped and the entire 
>> VFIO device
>> -data is transferred to the destination.
>> -
>> -The pre-copy phase of migration is currently not supported for VFIO 
>> devices.
>> -Support for VFIO pre-copy will be added later on.
>> +Migration of VFIO devices consists of two phases: the optional 
>> pre-copy phase,
>> +and the stop-and-copy phase. The pre-copy phase is iterative and 
>> allows to
>> +accommodate VFIO devices that have a large amount of data that needs 
>> to be
>> +transferred. The iterative pre-copy phase of migration allows for 
>> the guest to
>> +continue whilst the VFIO device state is transferred to the 
>> destination, this
>> +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.
>>
>>   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
>> @@ -29,10 +31,20 @@ VFIO implements the device hooks for the 
>> iterative approach as follows:
>>   * A ``load_setup`` function that sets the VFIO device on the 
>> destination in
>>     _RESUMING state.
>>
>> +* A ``state_pending_estimate`` function that reports an estimate of the
>> +  remaining pre-copy data that the vendor driver has yet to save for 
>> the VFIO
>> +  device.
>> +
>>   * A ``state_pending_exact`` function that reads pending_bytes from 
>> the vendor
>>     driver, which indicates the amount of data that the vendor driver 
>> has yet to
>>     save for the VFIO device.
>>
>> +* An ``is_active_iterate`` function that indicates 
>> ``save_live_iterate`` is
>> +  active only when the VFIO device is in pre-copy states.
>> +
>> +* A ``save_live_iterate`` function that reads the VFIO device's data 
>> from the
>> +  vendor driver during iterative pre-copy phase.
>> +
>>   * 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
>> @@ -111,8 +123,10 @@ Flow of state changes during Live migration
>>   ===========================================
>>
>>   Below is the flow of state change during live migration.
>> -The values in the brackets represent the VM state, the migration 
>> state, and
>> +The values in the parentheses represent the VM state, the migration 
>> state, and
>>   the VFIO device state, respectively.
>> +The text in the square brackets represents the flow if the VFIO 
>> device supports
>> +pre-copy.
>>
>>   Live migration save path
>>   ------------------------
>> @@ -124,11 +138,12 @@ Live migration save path
>>                                     |
>>                        migrate_init spawns migration_thread
>>                   Migration thread then calls each device's 
>> .save_setup()
>> -                       (RUNNING, _SETUP, _RUNNING)
>> +                  (RUNNING, _SETUP, _RUNNING [_PRE_COPY])
>>                                     |
>> -                      (RUNNING, _ACTIVE, _RUNNING)
>> -             If device is active, get pending_bytes by 
>> .state_pending_exact()
>> +                  (RUNNING, _ACTIVE, _RUNNING [_PRE_COPY])
>> +      If device is active, get pending_bytes by 
>> .state_pending_{estimate,exact}()
>>             If total pending_bytes >= threshold_size, call 
>> .save_live_iterate()
>> +                  [Data of VFIO device for pre-copy phase is copied]
>>           Iterate till total pending bytes converge and are less than 
>> threshold
>>                                     |
>>     On migration completion, vCPU stops and calls 
>> .save_live_complete_precopy for
>> diff --git a/include/hw/vfio/vfio-common.h 
>> b/include/hw/vfio/vfio-common.h
>> index 5f29dab839..1db901c194 100644
>> --- a/include/hw/vfio/vfio-common.h
>> +++ b/include/hw/vfio/vfio-common.h
>> @@ -67,6 +67,8 @@ typedef struct VFIOMigration {
>>       void *data_buffer;
>>       size_t data_buffer_size;
>>       uint64_t mig_flags;
>> +    uint64_t precopy_init_size;
>> +    uint64_t precopy_dirty_size;
>>   } VFIOMigration;
>>
>>   typedef struct VFIOAddressSpace {
>> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
>> index 78358ede27..b73086e17a 100644
>> --- a/hw/vfio/common.c
>> +++ b/hw/vfio/common.c
>> @@ -492,7 +492,8 @@ static bool 
>> vfio_devices_all_dirty_tracking(VFIOContainer *container)
>>               }
>>
>>               if (vbasedev->pre_copy_dirty_page_tracking == 
>> ON_OFF_AUTO_OFF &&
>> -                migration->device_state == VFIO_DEVICE_STATE_RUNNING) {
>> +                (migration->device_state == 
>> VFIO_DEVICE_STATE_RUNNING ||
>> +                 migration->device_state == 
>> VFIO_DEVICE_STATE_PRE_COPY)) {
>>                   return false;
>>               }
>>           }
>> @@ -537,7 +538,8 @@ static bool 
>> vfio_devices_all_running_and_mig_active(VFIOContainer *container)
>>                   return false;
>>               }
>>
>> -            if (migration->device_state == VFIO_DEVICE_STATE_RUNNING) {
>> +            if (migration->device_state == VFIO_DEVICE_STATE_RUNNING ||
>> +                migration->device_state == 
>> VFIO_DEVICE_STATE_PRE_COPY) {
>>                   continue;
>>               } else {
>>                   return false;
>> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
>> index 8d33414379..d8f6a22ae1 100644
>> --- a/hw/vfio/migration.c
>> +++ b/hw/vfio/migration.c
>> @@ -68,6 +68,8 @@ static const char *mig_state_to_str(enum 
>> vfio_device_mig_state state)
>>           return "STOP_COPY";
>>       case VFIO_DEVICE_STATE_RESUMING:
>>           return "RESUMING";
>> +    case VFIO_DEVICE_STATE_PRE_COPY:
>> +        return "PRE_COPY";
>>       default:
>>           return "UNKNOWN STATE";
>>       }
>> @@ -241,6 +243,25 @@ static int vfio_query_stop_copy_size(VFIODevice 
>> *vbasedev,
>>       return 0;
>>   }
>>
>> +static int vfio_query_precopy_size(VFIOMigration *migration)
>> +{
>> +    struct vfio_precopy_info precopy = {
>> +        .argsz = sizeof(precopy),
>> +    };
>> +
>> +    migration->precopy_init_size = 0;
>> +    migration->precopy_dirty_size = 0;
>> +
>> +    if (ioctl(migration->data_fd, VFIO_MIG_GET_PRECOPY_INFO, 
>> &precopy)) {
>> +        return -errno;
>> +    }
>> +
>> +    migration->precopy_init_size = precopy.initial_bytes;
>> +    migration->precopy_dirty_size = precopy.dirty_bytes;
>> +
>> +    return 0;
>> +}
>> +
>>   /* Returns the size of saved data on success and -errno on error */
>>   static ssize_t vfio_save_block(QEMUFile *f, VFIOMigration *migration)
>>   {
>> @@ -249,6 +270,14 @@ static ssize_t vfio_save_block(QEMUFile *f, 
>> VFIOMigration *migration)
>>       data_size = read(migration->data_fd, migration->data_buffer,
>>                        migration->data_buffer_size);
>>       if (data_size < 0) {
>> +        /*
>> +         * Pre-copy emptied all the device state for now. For more 
>> information,
>> +         * please refer to the Linux kernel VFIO uAPI.
>> +         */
>> +        if (errno == ENOMSG) {
>> +            return 0;
>> +        }
>> +
>>           return -errno;
>>       }
>>       if (data_size == 0) {
>> @@ -265,6 +294,38 @@ static ssize_t vfio_save_block(QEMUFile *f, 
>> VFIOMigration *migration)
>>       return qemu_file_get_error(f) ?: data_size;
>>   }
>>
>> +static void vfio_update_estimated_pending_data(VFIOMigration 
>> *migration,
>> +                                               uint64_t data_size)
>> +{
>> +    if (!data_size) {
>> +        /*
>> +         * Pre-copy emptied all the device state for now, update 
>> estimated sizes
>> +         * accordingly.
>> +         */
>> +        migration->precopy_init_size = 0;
>> +        migration->precopy_dirty_size = 0;
>> +
>> +        return;
>> +    }
>> +
>> +    if (migration->precopy_init_size) {
>> +        uint64_t init_size = MIN(migration->precopy_init_size, 
>> data_size);
>> +
>> +        migration->precopy_init_size -= init_size;
>> +        data_size -= init_size;
>> +    }
>> +
>> +    migration->precopy_dirty_size -= MIN(migration->precopy_dirty_size,
>> +                                         data_size);
>> +}
>> +
>> +static bool vfio_precopy_supported(VFIODevice *vbasedev)
>> +{
>> +    VFIOMigration *migration = vbasedev->migration;
>> +
>> +    return migration->mig_flags & VFIO_MIGRATION_PRE_COPY;
>> +}
>> +
>>   /* 
>> ---------------------------------------------------------------------- 
>> */
>>
>>   static int vfio_save_setup(QEMUFile *f, void *opaque)
>> @@ -285,6 +346,28 @@ static int vfio_save_setup(QEMUFile *f, void 
>> *opaque)
>>           return -ENOMEM;
>>       }
>>
>> +    if (vfio_precopy_supported(vbasedev)) {
>> +        int ret;
>> +
>> +        switch (migration->device_state) {
>> +        case VFIO_DEVICE_STATE_RUNNING:
>> +            ret = vfio_migration_set_state(vbasedev, 
>> VFIO_DEVICE_STATE_PRE_COPY,
>> + VFIO_DEVICE_STATE_RUNNING);
>> +            if (ret) {
>> +                return ret;
>> +            }
>> +
>> +            vfio_query_precopy_size(migration);
>> +
>> +            break;
>> +        case VFIO_DEVICE_STATE_STOP:
>> +            /* vfio_save_complete_precopy() will go to STOP_COPY */
>> +            break;
>> +        default:
>> +            return -EINVAL;
>> +        }
>> +    }
>> +
>>       trace_vfio_save_setup(vbasedev->name, 
>> migration->data_buffer_size);
>>
>>       qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
>> @@ -299,26 +382,42 @@ static void vfio_save_cleanup(void *opaque)
>>
>>       g_free(migration->data_buffer);
>>       migration->data_buffer = NULL;
>> +    migration->precopy_init_size = 0;
>> +    migration->precopy_dirty_size = 0;
>>       vfio_migration_cleanup(vbasedev);
>>       trace_vfio_save_cleanup(vbasedev->name);
>>   }
>>
>> +static void vfio_state_pending_estimate(void *opaque, uint64_t 
>> *must_precopy,
>> +                                        uint64_t *can_postcopy)
>> +{
>> +    VFIODevice *vbasedev = opaque;
>> +    VFIOMigration *migration = vbasedev->migration;
>> +
>> +    if (migration->device_state != VFIO_DEVICE_STATE_PRE_COPY) {
>> +        return;
>> +    }
>> +
>> +    *must_precopy +=
>> +        migration->precopy_init_size + migration->precopy_dirty_size;
>> +
>> +    trace_vfio_state_pending_estimate(vbasedev->name, *must_precopy,
>> +                                      *can_postcopy,
>> + migration->precopy_init_size,
>> + migration->precopy_dirty_size);
>> +}
>> +
>>   /*
>>    * Migration size of VFIO devices can be as little as a few KBs or 
>> as big as
>>    * many GBs. This value should be big enough to cover the worst case.
>>    */
>>   #define VFIO_MIG_STOP_COPY_SIZE (100 * GiB)
>>
>> -/*
>> - * Only exact function is implemented and not estimate function. The 
>> reason is
>> - * that during pre-copy phase of migration the estimate function is 
>> called
>> - * repeatedly while pending RAM size is over the threshold, thus 
>> migration
>> - * can't converge and querying the VFIO device pending data size is 
>> useless.
>> - */
>>   static void vfio_state_pending_exact(void *opaque, uint64_t 
>> *must_precopy,
>>                                        uint64_t *can_postcopy)
>>   {
>>       VFIODevice *vbasedev = opaque;
>> +    VFIOMigration *migration = vbasedev->migration;
>>       uint64_t stop_copy_size = VFIO_MIG_STOP_COPY_SIZE;
>>
>>       /*
>> @@ -328,8 +427,48 @@ static void vfio_state_pending_exact(void 
>> *opaque, uint64_t *must_precopy,
>>       vfio_query_stop_copy_size(vbasedev, &stop_copy_size);
>>       *must_precopy += stop_copy_size;
>>
>> +    if (migration->device_state == VFIO_DEVICE_STATE_PRE_COPY) {
>> +        vfio_query_precopy_size(migration);
>> +
>> +        *must_precopy +=
>> +            migration->precopy_init_size + 
>> migration->precopy_dirty_size;
>> +    }
>> +
>>       trace_vfio_state_pending_exact(vbasedev->name, *must_precopy, 
>> *can_postcopy,
>> -                                   stop_copy_size);
>> +                                   stop_copy_size, 
>> migration->precopy_init_size,
>> + migration->precopy_dirty_size);
>> +}
>> +
>> +static bool vfio_is_active_iterate(void *opaque)
>> +{
>> +    VFIODevice *vbasedev = opaque;
>> +    VFIOMigration *migration = vbasedev->migration;
>> +
>> +    return migration->device_state == VFIO_DEVICE_STATE_PRE_COPY;
>> +}
>> +
>> +static int vfio_save_iterate(QEMUFile *f, void *opaque)
>> +{
>> +    VFIODevice *vbasedev = opaque;
>> +    VFIOMigration *migration = vbasedev->migration;
>> +    ssize_t data_size;
>> +
>> +    data_size = vfio_save_block(f, migration);
>> +    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);
>> +
>> +    trace_vfio_save_iterate(vbasedev->name, 
>> migration->precopy_init_size,
>> +                            migration->precopy_dirty_size);
>> +
>> +    /*
>> +     * A VFIO device's pre-copy dirty_bytes is not guaranteed to 
>> reach zero.
>> +     * Return 1 so following handlers will not be potentially blocked.
>> +     */
>> +    return 1;
>>   }
>>
>>   static int vfio_save_complete_precopy(QEMUFile *f, void *opaque)
>> @@ -338,7 +477,7 @@ static int vfio_save_complete_precopy(QEMUFile 
>> *f, void *opaque)
>>       ssize_t data_size;
>>       int ret;
>>
>> -    /* We reach here with device state STOP only */
>> +    /* We reach here with device state STOP or STOP_COPY only */
>>       ret = vfio_migration_set_state(vbasedev, 
>> VFIO_DEVICE_STATE_STOP_COPY,
>>                                      VFIO_DEVICE_STATE_STOP);
>>       if (ret) {
>> @@ -457,7 +596,10 @@ static int vfio_load_state(QEMUFile *f, void 
>> *opaque, int version_id)
>>   static const SaveVMHandlers savevm_vfio_handlers = {
>>       .save_setup = vfio_save_setup,
>>       .save_cleanup = vfio_save_cleanup,
>> +    .state_pending_estimate = vfio_state_pending_estimate,
>>       .state_pending_exact = vfio_state_pending_exact,
>> +    .is_active_iterate = vfio_is_active_iterate,
>> +    .save_live_iterate = vfio_save_iterate,
>>       .save_live_complete_precopy = vfio_save_complete_precopy,
>>       .save_state = vfio_save_state,
>>       .load_setup = vfio_load_setup,
>> @@ -470,13 +612,18 @@ static const SaveVMHandlers 
>> savevm_vfio_handlers = {
>>   static void vfio_vmstate_change(void *opaque, bool running, 
>> RunState state)
>>   {
>>       VFIODevice *vbasedev = opaque;
>> +    VFIOMigration *migration = vbasedev->migration;
>>       enum vfio_device_mig_state new_state;
>>       int ret;
>>
>>       if (running) {
>>           new_state = VFIO_DEVICE_STATE_RUNNING;
>>       } else {
>> -        new_state = VFIO_DEVICE_STATE_STOP;
>> +        new_state =
>> +            (migration->device_state == VFIO_DEVICE_STATE_PRE_COPY &&
>> +             (state == RUN_STATE_FINISH_MIGRATE || state == 
>> RUN_STATE_PAUSED)) ?
>> +                VFIO_DEVICE_STATE_STOP_COPY :
>> +                VFIO_DEVICE_STATE_STOP;
>>       }
>>
>>       /*
>> diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
>> index 646e42fd27..548f9488a7 100644
>> --- a/hw/vfio/trace-events
>> +++ b/hw/vfio/trace-events
>> @@ -162,6 +162,8 @@ vfio_save_block(const char *name, int data_size) 
>> " (%s) data_size %d"
>>   vfio_save_cleanup(const char *name) " (%s)"
>>   vfio_save_complete_precopy(const char *name, int ret) " (%s) ret %d"
>>   vfio_save_device_config_state(const char *name) " (%s)"
>> +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"
>
> the extra '"' at the end breaks compile. No need to resend just for that.
> It can be fixed.
>
Oh, strange that it doesn't break when I compile it.
Do you have any idea why would  that be?

Thanks!

>
>
>>   vfio_save_setup(const char *name, uint64_t data_buffer_size) " (%s) 
>> data buffer size 0x%"PRIx64
>> -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
>> +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
>> +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
>>   vfio_vmstate_change(const char *name, int running, const char 
>> *reason, const char *dev_state) " (%s) running %d reason %s device 
>> state %s"
>

Re: [PATCH v4 9/9] vfio/migration: Add support for switchover ack capability

[Cédric Le Goater]

On 5/28/23 16:06, Avihai Horon wrote:
> 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.
> 
> As precopy support and precopy initial bytes support come together in
> VFIO migration, use x-allow-pre-copy device property to control usage of
> this feature as well.
> 
> Signed-off-by: Avihai Horon <avihaih@nvidia.com>
> ---
>   docs/devel/vfio-migration.rst | 10 ++++++++
>   include/hw/vfio/vfio-common.h |  2 ++
>   hw/vfio/migration.c           | 48 ++++++++++++++++++++++++++++++++++-
>   3 files changed, 59 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/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> index a53ecbe2e0..ad0562c8b7 100644
> --- a/include/hw/vfio/vfio-common.h
> +++ b/include/hw/vfio/vfio-common.h
> @@ -69,6 +69,8 @@ typedef struct VFIOMigration {
>       uint64_t mig_flags;
>       uint64_t precopy_init_size;
>       uint64_t precopy_dirty_size;
> +    bool switchover_ack_needed;

Do we really need the 'switchover_ack_needed' bool ?

It seems that each time it is used in a routine it could be computed
locally with migrate_switchover_ack() and vfio_precopy_supported().
This would simplify the code a bit more.

Thanks,

C.


  
> +    bool initial_data_sent;
>   } VFIOMigration;
>   
>   typedef struct VFIOAddressSpace {
> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> index cb6923ed3f..ede29ffb5c 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
> @@ -218,6 +221,7 @@ static void vfio_migration_cleanup(VFIODevice *vbasedev)
>   
>       close(migration->data_fd);
>       migration->data_fd = -1;
> +    migration->switchover_ack_needed = false;
>   }
>   
>   static int vfio_query_stop_copy_size(VFIODevice *vbasedev,
> @@ -350,6 +354,10 @@ static int vfio_save_setup(QEMUFile *f, void *opaque)
>       if (vfio_precopy_supported(vbasedev)) {
>           int ret;
>   
> +        if (migrate_switchover_ack()) {
> +            migration->switchover_ack_needed = true;
> +        }
> +
>           switch (migration->device_state) {
>           case VFIO_DEVICE_STATE_RUNNING:
>               ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_PRE_COPY,
> @@ -385,6 +393,7 @@ 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);
>   }
> @@ -458,10 +467,17 @@ 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 (migration->switchover_ack_needed && !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);
>   
> @@ -526,6 +542,10 @@ static int vfio_load_setup(QEMUFile *f, void *opaque)
>   {
>       VFIODevice *vbasedev = opaque;
>   
> +    if (migrate_switchover_ack() && vfio_precopy_supported(vbasedev)) {
> +        vbasedev->migration->switchover_ack_needed = true;
> +    }
> +
>       return vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_RESUMING,
>                                      vbasedev->migration->device_state);
>   }
> @@ -580,6 +600,23 @@ static int vfio_load_state(QEMUFile *f, void *opaque, int version_id)
>               }
>               break;
>           }
> +        case VFIO_MIG_FLAG_DEV_INIT_DATA_SENT:
> +        {
> +            if (!vbasedev->migration->switchover_ack_needed) {
> +                error_report("%s: Received INIT_DATA_SENT but switchover ack "
> +                             "is not needed", 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;
> @@ -594,6 +631,14 @@ 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;
> +    VFIOMigration *migration = vbasedev->migration;
> +
> +    return migration->switchover_ack_needed;
> +}
> +
>   static const SaveVMHandlers savevm_vfio_handlers = {
>       .save_setup = vfio_save_setup,
>       .save_cleanup = vfio_save_cleanup,
> @@ -606,6 +651,7 @@ 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,
>   };
>   
>   /* ---------------------------------------------------------------------- */

Re: [PATCH v4 7/9] vfio/migration: Add VFIO migration pre-copy support

[Cédric Le Goater]

>>> diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
>>> index 646e42fd27..548f9488a7 100644
>>> --- a/hw/vfio/trace-events
>>> +++ b/hw/vfio/trace-events
>>> @@ -162,6 +162,8 @@ vfio_save_block(const char *name, int data_size) " (%s) data_size %d"
>>>   vfio_save_cleanup(const char *name) " (%s)"
>>>   vfio_save_complete_precopy(const char *name, int ret) " (%s) ret %d"
>>>   vfio_save_device_config_state(const char *name) " (%s)"
>>> +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"
>>
>> the extra '"' at the end breaks compile. No need to resend just for that.
>> It can be fixed.
>>
> Oh, strange that it doesn't break when I compile it.
> Do you have any idea why would  that be?

It generates a -Werror=format= .

Did you configure the build with  --disable-werror  ?


C.

Re: [PATCH v4 9/9] vfio/migration: Add support for switchover ack capability

[Avihai Horon]

On 30/05/2023 12:58, Cédric Le Goater wrote:
> External email: Use caution opening links or attachments
>
>
> On 5/28/23 16:06, Avihai Horon wrote:
>> 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.
>>
>> As precopy support and precopy initial bytes support come together in
>> VFIO migration, use x-allow-pre-copy device property to control usage of
>> this feature as well.
>>
>> Signed-off-by: Avihai Horon <avihaih@nvidia.com>
>> ---
>>   docs/devel/vfio-migration.rst | 10 ++++++++
>>   include/hw/vfio/vfio-common.h |  2 ++
>>   hw/vfio/migration.c           | 48 ++++++++++++++++++++++++++++++++++-
>>   3 files changed, 59 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/include/hw/vfio/vfio-common.h 
>> b/include/hw/vfio/vfio-common.h
>> index a53ecbe2e0..ad0562c8b7 100644
>> --- a/include/hw/vfio/vfio-common.h
>> +++ b/include/hw/vfio/vfio-common.h
>> @@ -69,6 +69,8 @@ typedef struct VFIOMigration {
>>       uint64_t mig_flags;
>>       uint64_t precopy_init_size;
>>       uint64_t precopy_dirty_size;
>> +    bool switchover_ack_needed;
>
> Do we really need the 'switchover_ack_needed' bool ?
>
> It seems that each time it is used in a routine it could be computed
> locally with migrate_switchover_ack() and vfio_precopy_supported().
> This would simplify the code a bit more.
>
You are right.
I will drop it and send a v5 (will fix the superfluous " as well).

Thanks!

>
>
>
>> +    bool initial_data_sent;
>>   } VFIOMigration;
>>
>>   typedef struct VFIOAddressSpace {
>> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
>> index cb6923ed3f..ede29ffb5c 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
>> @@ -218,6 +221,7 @@ static void vfio_migration_cleanup(VFIODevice 
>> *vbasedev)
>>
>>       close(migration->data_fd);
>>       migration->data_fd = -1;
>> +    migration->switchover_ack_needed = false;
>>   }
>>
>>   static int vfio_query_stop_copy_size(VFIODevice *vbasedev,
>> @@ -350,6 +354,10 @@ static int vfio_save_setup(QEMUFile *f, void 
>> *opaque)
>>       if (vfio_precopy_supported(vbasedev)) {
>>           int ret;
>>
>> +        if (migrate_switchover_ack()) {
>> +            migration->switchover_ack_needed = true;
>> +        }
>> +
>>           switch (migration->device_state) {
>>           case VFIO_DEVICE_STATE_RUNNING:
>>               ret = vfio_migration_set_state(vbasedev, 
>> VFIO_DEVICE_STATE_PRE_COPY,
>> @@ -385,6 +393,7 @@ 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);
>>   }
>> @@ -458,10 +467,17 @@ 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 (migration->switchover_ack_needed && 
>> !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);
>>
>> @@ -526,6 +542,10 @@ static int vfio_load_setup(QEMUFile *f, void 
>> *opaque)
>>   {
>>       VFIODevice *vbasedev = opaque;
>>
>> +    if (migrate_switchover_ack() && vfio_precopy_supported(vbasedev)) {
>> +        vbasedev->migration->switchover_ack_needed = true;
>> +    }
>> +
>>       return vfio_migration_set_state(vbasedev, 
>> VFIO_DEVICE_STATE_RESUMING,
>> vbasedev->migration->device_state);
>>   }
>> @@ -580,6 +600,23 @@ static int vfio_load_state(QEMUFile *f, void 
>> *opaque, int version_id)
>>               }
>>               break;
>>           }
>> +        case VFIO_MIG_FLAG_DEV_INIT_DATA_SENT:
>> +        {
>> +            if (!vbasedev->migration->switchover_ack_needed) {
>> +                error_report("%s: Received INIT_DATA_SENT but 
>> switchover ack "
>> +                             "is not needed", 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;
>> @@ -594,6 +631,14 @@ 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;
>> +    VFIOMigration *migration = vbasedev->migration;
>> +
>> +    return migration->switchover_ack_needed;
>> +}
>> +
>>   static const SaveVMHandlers savevm_vfio_handlers = {
>>       .save_setup = vfio_save_setup,
>>       .save_cleanup = vfio_save_cleanup,
>> @@ -606,6 +651,7 @@ 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,
>>   };
>>
>>   /* 
>> ---------------------------------------------------------------------- 
>> */
>

Re: [PATCH v4 7/9] vfio/migration: Add VFIO migration pre-copy support

[Avihai Horon]

On 30/05/2023 13:17, Cédric Le Goater wrote:
> External email: Use caution opening links or attachments
>
>
>>>> diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
>>>> index 646e42fd27..548f9488a7 100644
>>>> --- a/hw/vfio/trace-events
>>>> +++ b/hw/vfio/trace-events
>>>> @@ -162,6 +162,8 @@ vfio_save_block(const char *name, int 
>>>> data_size) " (%s) data_size %d"
>>>>   vfio_save_cleanup(const char *name) " (%s)"
>>>>   vfio_save_complete_precopy(const char *name, int ret) " (%s) ret %d"
>>>>   vfio_save_device_config_state(const char *name) " (%s)"
>>>> +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"
>>>
>>> the extra '"' at the end breaks compile. No need to resend just for 
>>> that.
>>> It can be fixed.
>>>
>> Oh, strange that it doesn't break when I compile it.
>> Do you have any idea why would  that be?
>
> It generates a -Werror=format= .
>
> Did you configure the build with  --disable-werror  ?

Nope.

configure prints this:
User defined options
     [...]
     werror                          : true