[libvirt] Preferred CPU model not allowed by hypervisor

[Andrew Cathrow]

----- Original Message -----
> From: "Jared" <list-virt at legroom.net>
> To: libvir-list at redhat.com
> Sent: Saturday, July 21, 2012 5:46:18 AM
> Subject: [libvirt] Preferred CPU model not allowed by hypervisor
> 
> Hi.
> 
> I'm having a weird problem where libvirt/qemu/kvm won't let me use
> the model
> processor I have defined in my domain's config file.  Instead, I get
> the
> error message in libvirtd.log that:
> 
> warning : x86Decode:1346 : Preferred CPU model Nehalem not allowed by
> hypervisor; closest supported model will be used
> 
> If I review the qemu log for that particular domain, I see that my
> CPU has
> been changed to this:
> 
> -cpu kvm64,+lahf_lm,+popcnt,+sse4.2,+sse4.1,+ssse3
> 
> (in other places, I see it set to core2duo rather than kvm64)
> 
> However, it *should* be Nehalem.  For some background, I'm running
> lvm on a
> westmere proc, which is the successor to Nehalem.  I'm specifying
> Nehalem as
> the target platform, though, to make it easier to migrate to another
> server
> if necessary.  I do have this same problem if I set this to Westmere,
> though, so it's not unique to Nehalem.
> 
> As for support and capabilities, libvirt correctly detects my host
> CPU as
> Westmere:
> 
> $ virsh capabilities | grep model
>       <model>Westmere</model>
> 
> qemu-kvm does (as far as I can tell) support Nehalem:
> 
> $ qemu-kvm -cpu ?model | grep Nehalem
> x86          Nehalem  Intel Core i7 9xx (Nehalem Class Core i7)
> 
> Nehalem is defined in qmeu's target-x86_64.conf:
> 
> grep Nehalem /etc/qemu/target-x86_64.conf
>    name = "Nehalem"
>    model_id = "Intel Core i7 9xx (Nehalem Class Core i7)"
> 
> And if I run a cpu check on the processor, it seems to work fine:
> 
> $ qemu-kvm -cpu Nehalem,check
> VNC server running on `127.0.0.1:5900'
> 
> So, I I'm creating the new domain as a virt-install with the qemu-kvm
> backend as follows:
> 
> virt-install --name=test --ram=1024 --arch=x86_64 --vcpus=2
> --cpu=Nehalem
> --virt-type=kvm <SNIP>
> 
> This results in the following cpu configuration:
>   <cpu mode='custom' match='exact'>
>     <model fallback='allow'>Nehalem</model>
>   </cpu>
> 
> 
> But then, when I start this domain, I get the error message posted
> above.
> 
> Any ideas what's going on here?  I'm at a loss, and unfortunately I
> don't
> have much experience with kvm/libvirt just yet so I don't know what I
> should
> be focusing on for troubleshooting.  Would appreciate any suggestions
> or
> guidance.

Have a look here

https://bugzilla.redhat.com/show_bug.cgi?id=804224



> 
> Thanks.
> 
> --
> Jared
> 
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