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

[Jan Kiszka]

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that this switch is obsolete and will be removed from future versions.

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

Jan

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