On 19.11.20 13:02, Christian Borntraeger wrote:

On 16.11.20 16:34, Catangiu, Adrian Costin wrote:

quoted

- Background

The VM Generation ID is a feature defined by Microsoft (paper:
http://go.microsoft.com/fwlink/?LinkId=260709) and supported by
multiple hypervisor vendors.

The feature is required in virtualized environments by apps that work
with local copies/caches of world-unique data such as random values,
uuids, monotonically increasing counters, etc.
Such apps can be negatively affected by VM snapshotting when the VM
is either cloned or returned to an earlier point in time.

The VM Generation ID is a simple concept meant to alleviate the issue
by providing a unique ID that changes each time the VM is restored
from a snapshot. The hw provided UUID value can be used to
differentiate between VMs or different generations of the same VM.

- Problem

The VM Generation ID is exposed through an ACPI device by multiple
hypervisor vendors but neither the vendors or upstream Linux have no
default driver for it leaving users to fend for themselves.

I see that the qemu implementation is still under discussion. What is

Uh, the ACPI Vmgenid device emulation is in QEMU since 2.9.0 :).

the status of the other existing implementations. Do they already exist?
In other words is ACPI a given?
I think the majority of this driver could be used with just a different
backend for platforms without ACPI so in any case we could factor out
the backend (acpi, virtio, whatever) but if we are open we could maybe
start with something else.

I agree 100%. I don't think we really need a new framework in the kernel 
for that. We can just have for example an s390x specific driver that 
also provides the same notification mechanism through a device node that 
is also named "/dev/vmgenid", no?

Or alternatively we can split the generic part of this driver as soon as 
a second one comes along and then have both driver include that generic 
logic.

The only piece where I'm unsure is how this will interact with CRIU. Can 
containers emulate ioctls and device nodes?


Alex



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