Re: [Qemu-devel] Cascadelake-Server missing MSR based features ?

[Daniel P . Berrangé]

On Tue, Mar 19, 2019 at 10:35:33PM +0800, Tao Xu wrote:
> On 3/19/2019 8:16 PM, Daniel P. Berrangé wrote:
> > The Cascadelake-Server CPU was added last year in
> > 
> >    commit c7a88b52f62b30c04158eeb07f73e3f72221b6a8
> >    Author: Tao Xu <address@hidden>
> >    Date:   Wed Sep 19 11:11:22 2018 +0800
> > 
> >      i386: Add new model of Cascadelake-Server
> > 
> > The commit message says that MSR based features are initially
> > omitted from its definition:
> > 
> >    [quote]
> >      On Cascadelake, some capabilities (RDCL_NO, IBRS_ALL, RSBA,
> >      SKIP_L1DFL_VMENTRY and SSB_NO) are enumerated by MSR.
> >      These features rely on MSR based feature support patch.
> >      Will be added later after that patch's in.
> >      http://lists.nongnu.org/archive/html/qemu-devel/2018-09/msg00074.html
> >    [/quote]

[snip]

> > Can anyone shed light on what the status is wrt exposing the MSR based
> > features in Cascadelake-Server ?
> 
> Hi, I sent the patch to add the MSR based features with the Update stepping
> patch together last year, and we discussed a lot about it:
> 
> [1] https://patchwork.kernel.org/patch/10743427/

Ahh, I see, so none of the MSR based feature stuff is migratable.

If migration isn't needed, then they can use "-cpu host" which gets all
features automatically.

If migration is needed, then the app is using a named CPU model, and no
MSR based features should ever be used.

Also means that libvirt must be careful to *not* enable MSR based
features with "host-model" as this is supposde to be a migratable
version of "host-passthrough"

Is there any ETA on fixing things so that the MSR features can be
used with named models ?

Regards,
Daniel
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