Re: [RFC V2 0/8] Live update: tap and vhost

[Steven Sistare <steven.sistare@oracle.com>]

On 8/5/2025 3:53 PM, Steven Sistare wrote:
> On 8/5/2025 9:54 AM, Fabiano Rosas wrote:
>> Steve Sistare <steven.sistare@oracle.com> writes:
>>
>>> Tap and vhost devices can be preserved during cpr-transfer using
>>> traditional live migration methods, wherein the management layer
>>> creates new interfaces for the target and fiddles with 'ip link'
>>> to deactivate the old interface and activate the new.
>>>
>>> However, CPR can simply send the file descriptors to new QEMU,
>>> with no special management actions required.  The user enables
>>> this behavior by specifing '-netdev tap,cpr=on'.  The default
>>> is cpr=off.
>>>
>>> Steve Sistare (8):
>>>    migration: stop vm earlier for cpr
>>>    migration: cpr setup notifier
>>>    vhost: reset vhost devices for cpr
>>>    cpr: delete all fds
>>>    Revert "vhost-backend: remove vhost_kernel_reset_device()"
>>>    tap: common return label
>>>    tap: cpr support
>>>    tap: postload fix for cpr
>>>
>>>   qapi/net.json             |   5 +-
>>>   include/hw/virtio/vhost.h |   1 +
>>>   include/migration/cpr.h   |   3 +-
>>>   include/net/tap.h         |   1 +
>>>   hw/net/virtio-net.c       |  20 +++++++
>>>   hw/vfio/device.c          |   2 +-
>>>   hw/virtio/vhost-backend.c |   6 ++
>>>   hw/virtio/vhost.c         |  32 +++++++++++
>>>   migration/cpr.c           |  24 ++++++--
>>>   migration/migration.c     |  38 ++++++++-----
>>>   net/tap-win32.c           |   5 ++
>>>   net/tap.c                 | 141 +++++++++++++++++++++++++++++++++++-----------
>>>   12 files changed, 223 insertions(+), 55 deletions(-)
>>
>> Hi Steve,
>>
>> Patches 1-2 seem to potentially interact with your arm pending
>> interrupts fix. Do we want them together?
> 
> Good observation, thanks!.  I may need patches 1-2 to completely close
> the dropped interrupt race.  I will do more testing to verify that.

aarch64 does not need patches 1-2 to fix interrupts.
It only relies on MIG_EVENT_PRECOPY_DONE, whose relative ordering is not
affected by patches 1-2.

So, the arm patch gicv3 V3 can be pulled.

I am still looking at patches 1-2 wrt x86 interrupts.

- Steve