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Re: [Bug 1915063] Re: Windows 10 wil not install using qemu-system-x86_6

From: Igor Mammedov
Subject: Re: [Bug 1915063] Re: Windows 10 wil not install using qemu-system-x86_64
Date: Tue, 6 Apr 2021 20:53:07 +0200

On Sat, 03 Apr 2021 16:52:13 -0000
Christian Ehrhardt  <1915063@bugs.launchpad.net> wrote:

> That is awesome David,
> qemu64 is like a very low common denominator with only very basic CPU 
> features.
> While "copy host" means "enable all you can".

Also it's worth to try setting real CPU topology for if EPYC cpu model is used.
i.e. use -smp with options that resemble a real EPYC cpu
(for number of core complexes is configured with 'dies' option in QEMU)

> We can surely work with that a bit, but until I get access to the same
> HW I need you to do it.
> If you run in a console `$virsh domcapabilities` it will spew some XML at 
> you. One of the sections will be for "host-model". In my case that looks like
>     <mode name='host-model' supported='yes'>
>       <model fallback='forbid'>Skylake-Client-IBRS</model>
>       <vendor>Intel</vendor>
>       <feature policy='require' name='ss'/>
>       <feature policy='require' name='vmx'/>
>       <feature policy='require' name='hypervisor'/>
> ...
>     </mode>
> That means a names CPU type (the one that is closest to what you have) and 
> some feature additionally enabled/disabled.
> If you could please post the full output you have, that can be useful.
> >From there you could go two steps.  
> 1. as you see in my example it will list some cpu features on top of the 
> named type.
>    If you remove them one by one you might be able to identify the single-cpu 
> featute
>    that breaks in your case.
> 2. The named CPU that you have also has a representation, it can be found in
>    /usr/share/libvirt/cpu_map...
>    That ill list all the CPU features that make up the named type.
>    If #1 wasn't sufficient, you can now add those to your guest definition 
> one by one in disabled 
>    state, example
>     <feature policy='disable' name='ss'/>
> A description of the underlying mechanism is here
> https://libvirt.org/formatdomain.html#cpu-model-and-topology

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