On 7/3/2026 12:16 PM, Philippe Mathieu-Daudé wrote:
External email: Use caution opening links or attachments
On 3/7/26 10:13, Avihai Horon wrote:
On 7/3/2026 5:07 AM, Philippe Mathieu-Daudé wrote:
External email: Use caution opening links or attachments
On 30/6/26 06:31, Cédric Le Goater wrote:
From: Avihai Horon <[email protected]>
According to VFIO uAPI, precopy initial_bytes is considered as
critical
data that should be transferred and loaded prior to moving to
STOP_COPY
state to ensure precopy phase would be effective.
As currently defined, initial_bytes can only decrease as it's being
read
from the data fd. However, there are cases where a new chunk of
initial_bytes should be transferred during precopy.
The new VFIO_PRECOPY_INFO_REINIT feature addresses this and allows
reporting a new value for initial_bytes regardless of any previously
reported values.
Implement VFIO_PRECOPY_INFO_REINIT feature:
1. Opt-in for VFIO_DEVICE_FEATURE_MIG_PRECOPY_INFOv2 to make
VFIO_PRECOPY_INFO_REINIT available.
2. Request a new switchover ACK if initial_bytes increases post of a
previous switchover ACK. This ensures the device is not moved to
STOP_COPY before initial_bytes has reached zero again.
Acked-by: Peter Xu <[email protected]>
Signed-off-by: Avihai Horon <[email protected]>
Link:
https://lore.kernel.org/qemu-devel/20260622101214.25770-13-
[email protected]
Signed-off-by: Cédric Le Goater <[email protected]>
---
docs/devel/migration/vfio.rst | 14 +++++++
hw/vfio/vfio-migration-internal.h | 1 +
hw/vfio/migration.c | 68
++++++++++++++++++++++++++++---
hw/vfio/trace-events | 4 +-
4 files changed, 80 insertions(+), 7 deletions(-)
+/* Returns 1 on success, 0 if not supported and negative errno on
failure */
+static int vfio_migration_set_precopy_info_v2(VFIODevice *vbasedev)
+{
+ uint64_t buf[DIV_ROUND_UP(sizeof(struct vfio_device_feature),
+ sizeof(uint64_t))] = {};
What is the point of using uint64_t[] here?
Since there is no data payload in this case, it's mainly for consistency
with other VFIO_DEVICE_FEATURE ioctl call sites.
Ah, I didn't noticed. Does the VFIO_DEVICE_FEATURE ioctl expect
the buffer to be 64-bit aligned?
Nope.
AFAIU, the 64-bit alignment is for userspace, for the data payload to be
aligned, in case it holds some 64-bit members.
Thanks.
+ struct vfio_device_feature *feature = (struct
vfio_device_feature *)buf;
+
+ feature->argsz = sizeof(buf);
+ feature->flags =
+ VFIO_DEVICE_FEATURE_SET |
VFIO_DEVICE_FEATURE_MIG_PRECOPY_INFOv2;
+ if (ioctl(vbasedev->fd, VFIO_DEVICE_FEATURE, feature)) {
+ if (errno == ENOTTY) {
+ return 0;
+ }
+
+ return -errno;
+ }
+
+ return 1;
+}
