linux-kernel - Re: [PATCH v2] drivers/virt: vmgenid: add vm generation id driver

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Message-ID: <300d4404-3efe-880e-ef30-692eabbff5f7@de.ibm.com>
Date:   Thu, 19 Nov 2020 13:02:15 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     "Catangiu, Adrian Costin" <acatan@...zon.com>,
        "Graf (AWS), Alexander" <graf@...zon.de>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Jann Horn <jannh@...gle.com>
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        "MacCarthaigh, Colm" <colmmacc@...zon.com>,
        Andy Lutomirski <luto@...nel.org>,
        "Theodore Y. Ts'o" <tytso@....edu>,
        Eric Biggers <ebiggers@...nel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        "bonzini@....org" <bonzini@....org>,
        "Singh, Balbir" <sblbir@...zon.com>,
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Subject: Re: [PATCH v2] drivers/virt: vmgenid: add vm generation id driver


On 16.11.20 16:34, Catangiu, Adrian Costin wrote:
> - 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 
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.