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Re: [Qemu-devel] [PATCH 0/2] target-i386: "custom" CPU model + script to
From: |
Daniel P. Berrange |
Subject: |
Re: [Qemu-devel] [PATCH 0/2] target-i386: "custom" CPU model + script to dump existing CPU models |
Date: |
Tue, 9 Jun 2015 09:56:25 +0100 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Mon, Jun 08, 2015 at 10:18:35PM +0200, Jiri Denemark wrote:
> On Mon, Jun 08, 2015 at 16:07:38 -0300, Eduardo Habkost wrote:
> ...
> > libvirt can solve this problem partially by making sure every feature in a
> > CPU
> > model is explicitly configured, instead of (incorrectly) expecting that a
> > named
> > CPU model will never change in QEMU. But this doesn't solve the problem
> > completely, because it is still possible that new features unknown to
> > libvirt
> > get enabled in the default CPU model in future machine-types (that's very
> > likely to happen when we introduce new KVM features, for example).
> >
> > So, to make sure no new feature will be ever enabled without the knowledge
> > of
> > libvirt, add a "-cpu custom" mode, where no CPU model data is loaded at all,
> > and everything needs to be configured explicitly using CPU properties. That
> > means no CPU features will ever change depending on machine-type or
> > accelerator
> > capabilities when using "-cpu custom".
> >
> > * * *
> >
> > I know that this is basically the opposite of what we were aiming at in the
> > last few month^Wyears, where we were struggling to implement probing
> > interfaces
> > to expose machine-type-dependent data for libvirt. But, at least the fact
> > that
> > we could implement the new approach using a 9-line patch means we were still
> > going in the right direction. :)
> >
> > To help libvirt in the transition, a x86-cpu-model-dump script is provided,
> > that will generate a config file that can be loaded using -readconfig,
> > based on
> > the -cpu and -machine options provided in the command-line.
>
> Thanks Eduardo, I never was a big fan of moving (or copying) all the CPU
> configuration data to libvirt, but now I think it actually makes sense.
> We already have a partial copy of CPU model definitions in libvirt
> anyway, but as QEMU changes some CPU models in some machine types (and
> libvirt does not do that) we have no real control over the guest CPU
> configuration. While what we really want is full control to enforce
> stable guest ABI.
I meanwhile, always wanted the full CPU config data in libvirt, so that
we could ensure libvirt was able to use the exact same CPU model setup
on other hypervisors too - eg Xen, VMWare let us specify the CPUID masks
so we could re-use the libvirt data there.
> I will summarize my ideas on how libvirt should be using -cpu custom and
> send them to libvirt-list soon.
These patches are x86 obviously - is there anything we need to worry about
for non-x86 architectures I wonder ? IIRC, all the non-x86 archs have
traditionally only needed CPU model names and don't really have the same
level of per-flag CPUID mask configurability that x86 has.
Regards,
Daniel
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- [Qemu-devel] [PATCH 0/2] target-i386: "custom" CPU model + script to dump existing CPU models, Eduardo Habkost, 2015/06/08
- [Qemu-devel] [PATCH 1/2] target-i386: Introduce "-cpu custom", Eduardo Habkost, 2015/06/08
- [Qemu-devel] [PATCH 2/2] scripts: x86-cpu-model-dump script, Eduardo Habkost, 2015/06/08
- Re: [Qemu-devel] [PATCH 0/2] target-i386: "custom" CPU model + script to dump existing CPU models, Jiri Denemark, 2015/06/08
- Re: [Qemu-devel] [PATCH 0/2] target-i386: "custom" CPU model + script to dump existing CPU models,
Daniel P. Berrange <=
- Re: [Qemu-devel] [PATCH 0/2] target-i386: "custom" CPU model + script to dump existing CPU models, Andreas Färber, 2015/06/23
- Re: [Qemu-devel] [PATCH 0/2] target-i386: "custom" CPU model + script to dump existing CPU models, Eduardo Habkost, 2015/06/23
- Re: [Qemu-devel] [PATCH 0/2] target-i386: "custom" CPU model + script to dump existing CPU models, Michael S. Tsirkin, 2015/06/23
- Re: [Qemu-devel] [PATCH 0/2] target-i386: "custom" CPU model + script to dump existing CPU models, Eduardo Habkost, 2015/06/23
- Re: [Qemu-devel] [PATCH 0/2] target-i386: "custom" CPU model + script to dump existing CPU models, Andreas Färber, 2015/06/23
- Re: [Qemu-devel] [PATCH 0/2] target-i386: "custom" CPU model + script to dump existing CPU models, Daniel P. Berrange, 2015/06/23
- Re: [Qemu-devel] [PATCH 0/2] target-i386: "custom" CPU model + script to dump existing CPU models, Michael S. Tsirkin, 2015/06/23
- Re: [Qemu-devel] [PATCH 0/2] target-i386: "custom" CPU model + script to dump existing CPU models, Eduardo Habkost, 2015/06/23
- Re: [Qemu-devel] [PATCH 0/2] target-i386: "custom" CPU model + script to dump existing CPU models, Andreas Färber, 2015/06/23