Re: [Qemu-devel] drop -enable-nesting

[Avi Kivity <avi@redhat.com>]

On 05/30/2011 06:15 PM, Jan Kiszka wrote:
> On 2011-05-30 17:10, Roedel, Joerg wrote:
> >  On Mon, May 30, 2011 at 11:04:02AM -0400, Jan Kiszka wrote:
> >>  On 2011-05-30 16:38, Nadav Har'El wrote:
> >>>  On Mon, May 30, 2011, Jan Kiszka wrote about "drop -enable-nesting (was: [PATCH 3/7] cpu model bug fixes and definition corrections...)":
> >>>>  On 2011-05-30 10:18, Roedel, Joerg wrote:
> >>>>>  On Sat, May 28, 2011 at 04:39:13AM -0400, Jan Kiszka wrote:
> >>>>>
> >>>>>>  J�rg, how to deal with -enable-nesting in qemu-kvm to align behavior
> >>>>>>  with upstream?
> >>>>>
> >>>>>  My personal preference is to just remove it. In upstream-qemu it is
> >>>>>  enabled/disabled by +/-svm. -enable-nesting is just a historic thing
> >>>>>  which can be wiped out.
> >>>
> >>>  "-enable-nesting" could remain as a synonym for enabling either VMX or SVM
> >>>  in the guest, depending on what was available in the host (because KVM now
> >>>  supports both nested SVM and nested VMX, but not SVM-on-VMX or vice versa).
> >>
> >>  Why? Once nesting is stable (I think SVM already is), there is no reason
> >>  for an explicit enable. And you can always mask it out via -cpu.
> >>
> >>  BTW, what are the defaults for SVM right now in qemu-kvm and upstream?
> >>  Enable if the modeled CPU supports it?
> >
> >  qemu-kvm still needs -enable-nesting, otherwise it is disabled. Upstream
> >  qemu should enable it unconditionally (can be disabled with -cpu ,-svm).
>
> Then let's start with aligning qemu-kvm defaults to upstream? I guess
> that's what the diff I was citing yesterday is responsible for.
>
> In the same run, -enable-nesting could dump a warning on the console
> that this switch is obsolete and will be removed from future versions.

I think it's safe to drop -enable-nesting immediately.  Dan, does 
libvirt make use of it?

> For VMX, I would suggest to keep it off by default until it matured,
> asking the user to issue -cpu ...,+vmx.

We should do that for svm as well (except for -cpu host or -cpu 
something-with-svm).  vmx will be kept disabled by the module option, 
until it is deemed fit for general consumption.

-- 
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