drop -enable-nesting (was: [PATCH 3/7] cpu model bug fixes and definition corrections...)

drop -enable-nesting (was: [PATCH 3/7] cpu model bug fixes and definition corrections...)

[Jan Kiszka]

On 2011-05-30 10:18, Roedel, Joerg wrote:
> On Sat, May 28, 2011 at 04:39:13AM -0400, Jan Kiszka wrote:
> 
>> Jörg, 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.

Does any user land depend on it? I guess we have to flag it deprecated
first, trigger some console output when it's specified, and then remove
it one or more releases later (the same applies to many other
qemu-kvm-specific switches).

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

Re: drop -enable-nesting (was: [PATCH 3/7] cpu model bug fixes and definition corrections...)

[Nadav Har'El]

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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:
> > 
> >> Jörg, 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).

-- 
Nadav Har'El                        |       Monday, May 30 2011, 26 Iyyar 5771
nyh@math.technion.ac.il             |-----------------------------------------
Phone +972-523-790466, ICQ 13349191 |Software is like sex, it is better when
http://nadav.harel.org.il           |it's free -- Linus Torvalds

Re: drop -enable-nesting

[Jan Kiszka]

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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:
>>>
>>>> Jörg, 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?

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

Re: drop -enable-nesting

[Roedel, Joerg]

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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:
> >>>
> >>>> Jörg, 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).

	Joerg

-- 
AMD Operating System Research Center

Advanced Micro Devices GmbH Einsteinring 24 85609 Dornach
General Managers: Alberto Bozzo, Andrew Bowd
Registration: Dornach, Landkr. Muenchen; Registerger. Muenchen, HRB Nr. 43632

Re: 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

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

Re: drop -enable-nesting

[Avi Kivity]

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.

-- 
error compiling committee.c: too many arguments to function

Re: drop -enable-nesting

[Jan Kiszka]

On 2011-05-30 17:19, Avi Kivity wrote:
> 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?

I'm currently checking with some customer who played with Proxmox and
nesting if that stack was aware of the switch or accepted it only via a
side channel.

> 
>> 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).

I assume that's what upstream is doing. Maybe it has it was part of the
artificial default qemu64 model which is AMD based.

>  vmx will be kept disabled by the module option, 
> until it is deemed fit for general consumption.
> 

Yes, even better - no need for duplicate controls.

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

Re: drop -enable-nesting

[Jan Kiszka]

On 2011-05-30 17:27, Jan Kiszka wrote:
> On 2011-05-30 17:19, Avi Kivity wrote:
>> I think it's safe to drop -enable-nesting immediately.  Dan, does 
>> libvirt make use of it?
> 
> I'm currently checking with some customer who played with Proxmox and
> nesting if that stack was aware of the switch or accepted it only via a
> side channel.

It was a side channel for tweaking the command line options.

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

Re: drop -enable-nesting

[Daniel P. Berrange]

On Mon, May 30, 2011 at 06:19:14PM +0300, Avi Kivity wrote:
> 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?

Yes, but it should be safe to drop it. Currently, if the user specifies
a CPU with the 'svm' flag present in libvirt guest XML, then we will
pass args '-cpu ....+svm -enable-nesting'. So if we drop --enable-nesting,
then libvirt will simply omit it and everything should still work because
we have still got +svm set.

Daniel
-- 
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Re: drop -enable-nesting

[Avi Kivity]

On 05/31/2011 11:44 AM, Daniel P. Berrange wrote:
> >  I think it's safe to drop -enable-nesting immediately.  Dan, does
> >  libvirt make use of it?
>
> Yes, but it should be safe to drop it. Currently, if the user specifies
> a CPU with the 'svm' flag present in libvirt guest XML, then we will
> pass args '-cpu ....+svm -enable-nesting'. So if we drop --enable-nesting,
> then libvirt will simply omit it and everything should still work because
> we have still got +svm set.

But qemu will complain about an option it can't parse.

-- 
error compiling committee.c: too many arguments to function

Re: drop -enable-nesting

[Roedel, Joerg]

On Tue, May 31, 2011 at 04:58:16AM -0400, Avi Kivity wrote:
> On 05/31/2011 11:44 AM, Daniel P. Berrange wrote:
> > >  I think it's safe to drop -enable-nesting immediately.  Dan, does
> > >  libvirt make use of it?
> >
> > Yes, but it should be safe to drop it. Currently, if the user specifies
> > a CPU with the 'svm' flag present in libvirt guest XML, then we will
> > pass args '-cpu ....+svm -enable-nesting'. So if we drop --enable-nesting,
> > then libvirt will simply omit it and everything should still work because
> > we have still got +svm set.
> 
> But qemu will complain about an option it can't parse.

The best choice is probably to keep the option and make it a nop for the
lifetime of qemu-kvm. Optionally qemu-kvm can print a warning about the
deprecated option.

	Joerg

-- 
AMD Operating System Research Center

Advanced Micro Devices GmbH Einsteinring 24 85609 Dornach
General Managers: Alberto Bozzo, Andrew Bowd
Registration: Dornach, Landkr. Muenchen; Registerger. Muenchen, HRB Nr. 43632

Re: drop -enable-nesting

[Paolo Bonzini]

On 05/31/2011 10:58 AM, Avi Kivity wrote:
>
> But qemu will complain about an option it can't parse.

The presence of -enable-nesting is inferred from the help text.

Paolo

Re: drop -enable-nesting

[Avi Kivity]

On 05/31/2011 12:15 PM, Paolo Bonzini wrote:
> On 05/31/2011 10:58 AM, Avi Kivity wrote:
>>
>> But qemu will complain about an option it can't parse.
>
> The presence of -enable-nesting is inferred from the help text.


Okay, so it can be safely dropped.

-- 
error compiling committee.c: too many arguments to function

Re: drop -enable-nesting

[Nadav Har'El]

On Mon, May 30, 2011, Jan Kiszka wrote about "Re: drop -enable-nesting":
> > "-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.

As far as I understand (and this was previously discussed on the QEMU mailing
list), the default emulated CPU does not include the "vmx" capability, and you
need to enable it with something like "-cpu qemu64,+vmx" (or "-cpu host").

I am not sure if it does enable the "svm" capability. If it does, it isn't
useful when KVM is enabled and the underlying host has VMX, not SVM.

Nadav.

-- 
Nadav Har'El                        |       Monday, May 30 2011, 27 Iyyar 5771
nyh@math.technion.ac.il             |-----------------------------------------
Phone +972-523-790466, ICQ 13349191 |Why do we drive on a parkway and park on
http://nadav.harel.org.il           |a driveway?

Re: drop -enable-nesting

[Jan Kiszka]

On 2011-05-30 17:16, Nadav Har'El wrote:
> On Mon, May 30, 2011, Jan Kiszka wrote about "Re: drop -enable-nesting":
>>> "-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.
> 
> As far as I understand (and this was previously discussed on the QEMU mailing
> list), the default emulated CPU does not include the "vmx" capability, and you
> need to enable it with something like "-cpu qemu64,+vmx" (or "-cpu host").

qemu64 is an artificial AMD model. Adding VMX to it may have interesting
effects on the guests. Better use host or a recent Intel model.

> 
> I am not sure if it does enable the "svm" capability. If it does, it isn't
> useful when KVM is enabled and the underlying host has VMX, not SVM.

That's what KVM is supposed to filter based on the host's capabilities.
I bet it does already.

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux