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Re: [PATCH v2 2/2] s390x/cpumodel: Introduce dynamic feature groups

From: David Hildenbrand
Subject: Re: [PATCH v2 2/2] s390x/cpumodel: Introduce dynamic feature groups
Date: Tue, 26 Nov 2019 09:04:50 +0100

> Am 26.11.2019 um 08:54 schrieb Christian Borntraeger <address@hidden>:
>> On 25.11.19 18:20, David Hildenbrand wrote:
>> As soon as dynamic feature groups are used, the CPU model becomes
>> migration-unsafe. Upper layers can expand these models to migration-safe
>> and static variants, allowing them to be migrated.
> I really dislike that. I am trying to get rid of the unsafe variants (e.g. now
> defaulting to host-model instead of host-passthrough). I do not want to give
> users new ways of hurting themselves.

Please note that this is just on the bare command line. Libvirt and friends 
will expand the model and have proper migration in place. What exactly is your 
concern in that regard?

> Unless I misunderstood Eduardo, I think his versioning approach is actually 
> better
> in regard to migration, no?
> I z terms, you can still say -cpu z13  which is just an alias to z13v1 z13v2 
> etc.
> Assuming that the version is checked this will be safe.

It‘s even worse AFAIKS. A „-cpu z13“ would dynamically map to whatever is best 
on the host.

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