Re: [PATCH V1 00/32] Live Update

[Steven Sistare]

On 7/30/2020 1:15 PM, Paolo Bonzini wrote:
> On 30/07/20 17:14, Steve Sistare wrote:
>> The first set of patches adds the cprsave and cprload commands to save and
>> restore VM state, and allow the host kernel to be updated and rebooted in
>> between.  The VM must create guest RAM in a persistent shared memory file,
>> such as /dev/dax0.0 or persistant /dev/shm PKRAM as proposed in 
>> https://lore.kernel.org/lkml/1588812129-8596-1-git-send-email-anthony.yznaga@oracle.com/
>>
>> cprsave stops the VCPUs and saves VM device state in a simple file, and
>> thus supports any type of guest image and block device.  The caller must
>> not modify the VM's block devices between cprsave and cprload.
> 
> Stupid question, what does cpr stand for?  If it is checkpoint/restore,

Checkpoint/restart.  An acronym from my HPC days.  I will spell it out.

> please spell it out.  Also, how does the functionality compare to
> xen-save-devices-state and xen-load-devices-state?

qmp_xen_save_devices_state serializes device state to a file which is loaded 
on the target for a live migration.  It performs some of the same actions
as cprsave/cprload but does not support live update-in-place.

>> cprsave and cprload support guests with vfio devices if the caller first
>> suspends the guest by issuing guest-suspend-ram to the qemu guest agent.
>> The guest drivers suspend methods flush outstanding requests and re-
>> initialize the devices, and thus there is no device state to save and
>> restore.
> 
> This probably should be allowed even for regular migration.  Can you
> generalize the code as a separate series?

Maybe.  I think that would be a distinct patch that ignores the vfio migration 
blocker 
if the state is suspended.  Plus a qemu agent call to do the suspend.  Needs 
more
thought.

- Steve

> 
> Thanks,
> 
> Paolo
>