---
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"
