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Re: [qemu-s390x] [PATCH 02/10] s390x/cpumodel: remove CSSKE from base mo

From: Christian Borntraeger
Subject: Re: [qemu-s390x] [PATCH 02/10] s390x/cpumodel: remove CSSKE from base model
Date: Thu, 18 Apr 2019 15:00:53 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1

On 18.04.19 14:45, David Hildenbrand wrote:
> On 18.04.19 13:31, Christian Borntraeger wrote:
>> conditional sske is deprecated and a distant future machine (will be one
>> where the IBC will not allow to fully go back to z14) will remove this
>> feature. To prepare for this and allow for the z14 and older cpu model
>> to still run on systems without csske, remove csske from the base (and
> will csske feature be a default feature for zNext? Or is it not
> available *at all*.
> In case it is not available, baselining and cpu model comparison have to
> be thought about "ignoring csske".
>> thus the default models for z10..z14). For compat machines we have to
>> add those back.
> Base models are machine-independent. That means, changing base models is
> not supported.

Why is that? for the expansion?

> Once we introduce new models like here, we can set the
> new base models into stone.

the new model is easy (and yes I could only disable CSSKE in the base
model for gen15 but not for gen14. 

The problem is that without some kind of fixup for older base models like
z10-z14 expansion will fall back to z9 on anything that no longer has

> Instead of doing that, can we rather start generating the next
> generation "fresh", listing all base model features it contains instead
> of doing it incrementally? Could end up "nicer"
> In target/s390x/cpu_models.c we have:
> "... For now, base features of a following release are always a subset
> of base features of the previous release. Same is correct for the other
> feature sets."
> This is especially relevant for "s390_find_cpu_def", and goes into the
> direction of baselining, as previously mentioned.
> Luckily, we already have "ignored_base_feat", maybe we can simply add
> csske there and have it working.

Yes, maybe we could ignore csske. 

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