[v1] libxl: nestedhvm support

[libvirt] [PATCH v1 0/3] libxl: nestedhvm support

Posted by Wim Ten Have 7 years, 1 month ago

From: Wim ten Have <wim.ten.have@oracle.com>

This patch enhances host-passthrough capability to advertise the
required vendor CPU virtualization feature which will be used to
enable 'nestedhvm' in the libxl driver.

For Intel virtualization (VT-x)
    ..
  <cpu mode='host-passthrough'>
    <feature policy='require' name='vmx'/>
  </cpu>

For AMD virtualization (AMD-V)
    ..
  <cpu mode='host-passthrough'>
    <feature policy='require' name='svm'/>
  </cpu>

Joao Martins (2):
  libxl: set nestedhvm when vmx|svm is required
  xenconfig: add conversion of domxml nestedhvm

Wim ten Have (1):
  xlconfigtest: add test and data for 'nestedhvm' support

 src/libxl/libxl_conf.c                         |  9 ++++
 src/xenconfig/xen_xl.c                         | 41 +++++++++++++++++
 tests/xlconfigdata/test-fullvirt-nestedhvm.cfg | 26 +++++++++++
 tests/xlconfigdata/test-fullvirt-nestedhvm.xml | 61 ++++++++++++++++++++++++++
 tests/xlconfigtest.c                           |  1 +
 5 files changed, 138 insertions(+)
 create mode 100644 tests/xlconfigdata/test-fullvirt-nestedhvm.cfg
 create mode 100644 tests/xlconfigdata/test-fullvirt-nestedhvm.xml

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Re: [libvirt] [PATCH v1 0/3] libxl: nestedhvm support

Posted by Daniel P. Berrange 7 years, 1 month ago

On Wed, Mar 08, 2017 at 03:07:12PM +0100, Wim Ten Have wrote:
> From: Wim ten Have <wim.ten.have@oracle.com>
> 
> This patch enhances host-passthrough capability to advertise the
> required vendor CPU virtualization feature which will be used to
> enable 'nestedhvm' in the libxl driver.
> 
> For Intel virtualization (VT-x)
>     ..
>   <cpu mode='host-passthrough'>
>     <feature policy='require' name='vmx'/>
>   </cpu>
> 
> For AMD virtualization (AMD-V)
>     ..
>   <cpu mode='host-passthrough'>
>     <feature policy='require' name='svm'/>
>   </cpu>

If using host-passthrough or host-model, and the host's CPU includes
vmx or svm, then I would expecte nested-HVM to be enabled, without
needing any extra <feature> flag in the XML. That would match the
semantics used with the QEMU driver.

The only time we would need to use <feature> is if using mode=custom
along with a named CPU model which lacks vmx/svm flags.

BTW, I wonder how hard it would be to wire up the libxl driver to use
the CPU model infrastructure in src/cpu ? It feels a little odd to use
XML <cpu mode='host-passthrough'/> if we're not then making sure it
actually uses host-passthrough when configuring the guest.

Regards,
Daniel
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Re: [libvirt] [PATCH v1 0/3] libxl: nestedhvm support

Posted by Joao Martins 7 years, 1 month ago

On 03/08/2017 02:13 PM, Daniel P. Berrange wrote:
> On Wed, Mar 08, 2017 at 03:07:12PM +0100, Wim Ten Have wrote:
>> From: Wim ten Have <wim.ten.have@oracle.com>
>>
>> This patch enhances host-passthrough capability to advertise the
>> required vendor CPU virtualization feature which will be used to
>> enable 'nestedhvm' in the libxl driver.
>>
>> For Intel virtualization (VT-x)
>>     ..
>>   <cpu mode='host-passthrough'>
>>     <feature policy='require' name='vmx'/>
>>   </cpu>
>>
>> For AMD virtualization (AMD-V)
>>     ..
>>   <cpu mode='host-passthrough'>
>>     <feature policy='require' name='svm'/>
>>   </cpu>
> 
> If using host-passthrough or host-model, and the host's CPU includes
> vmx or svm, then I would expecte nested-HVM to be enabled, without
> needing any extra <feature> flag in the XML. That would match the
> semantics used with the QEMU driver.
> 
> The only time we would need to use <feature> is if using mode=custom
> along with a named CPU model which lacks vmx/svm flags.
Ah OK - I was kinda off unclear on that. So using host-passthrough should be
enough then. (while making sure libxl checks if host->cpu does have vmx or svm
in its features)

> BTW, I wonder how hard it would be to wire up the libxl driver to use
> the CPU model infrastructure in src/cpu ? It feels a little odd to use
> XML <cpu mode='host-passthrough'/> if we're not then making sure it
> actually uses host-passthrough when configuring the guest.
While xen libxl do allow to mangle the cpuid, it is meant for disabling features
at this point. libxl follows a "host-model" first, meaning the default is to
expose as much as features as possible to the guest (depending on whether it's
PV or HVM). However, nested virt is a slightly special case since the toolstack
will do more than simply unmasking vmx/svm bits (actually within libxl, a sysctl
to Xen is performed to enable nested virt to the domain, in which case libxc
will handle any vendor specific bits). IOW, even when we improve libxl cpuid
policy management to the point we can wire up to libvirt cpu model
infrastruture, we would still need to handle the nestedhvm special case (which
btw this field would work even for ARM whenever supported).

Joao

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Re: [libvirt] [PATCH v1 0/3] libxl: nestedhvm support

Posted by Daniel P. Berrange 7 years, 1 month ago

On Wed, Mar 08, 2017 at 03:09:11PM +0000, Joao Martins wrote:
> On 03/08/2017 02:13 PM, Daniel P. Berrange wrote:
> > On Wed, Mar 08, 2017 at 03:07:12PM +0100, Wim Ten Have wrote:
> >> From: Wim ten Have <wim.ten.have@oracle.com>
> >>
> >> This patch enhances host-passthrough capability to advertise the
> >> required vendor CPU virtualization feature which will be used to
> >> enable 'nestedhvm' in the libxl driver.
> >>
> >> For Intel virtualization (VT-x)
> >>     ..
> >>   <cpu mode='host-passthrough'>
> >>     <feature policy='require' name='vmx'/>
> >>   </cpu>
> >>
> >> For AMD virtualization (AMD-V)
> >>     ..
> >>   <cpu mode='host-passthrough'>
> >>     <feature policy='require' name='svm'/>
> >>   </cpu>
> > 
> > If using host-passthrough or host-model, and the host's CPU includes
> > vmx or svm, then I would expecte nested-HVM to be enabled, without
> > needing any extra <feature> flag in the XML. That would match the
> > semantics used with the QEMU driver.
> > 
> > The only time we would need to use <feature> is if using mode=custom
> > along with a named CPU model which lacks vmx/svm flags.
> Ah OK - I was kinda off unclear on that. So using host-passthrough should be
> enough then. (while making sure libxl checks if host->cpu does have vmx or svm
> in its features)
> 
> > BTW, I wonder how hard it would be to wire up the libxl driver to use
> > the CPU model infrastructure in src/cpu ? It feels a little odd to use
> > XML <cpu mode='host-passthrough'/> if we're not then making sure it
> > actually uses host-passthrough when configuring the guest.
> While xen libxl do allow to mangle the cpuid, it is meant for disabling features
> at this point. libxl follows a "host-model" first, meaning the default is to
> expose as much as features as possible to the guest (depending on whether it's
> PV or HVM). However, nested virt is a slightly special case since the toolstack
> will do more than simply unmasking vmx/svm bits (actually within libxl, a sysctl
> to Xen is performed to enable nested virt to the domain, in which case libxc
> will handle any vendor specific bits). IOW, even when we improve libxl cpuid
> policy management to the point we can wire up to libvirt cpu model
> infrastruture, we would still need to handle the nestedhvm special case (which
> btw this field would work even for ARM whenever supported).

Yep, I see. So with libxl using host-model by default, then

 - If the host CPU includes svm/vmx, turn on nested virt in the guest
 - Allow use of <feature name="vmx" policy="disable"/> to block nested
   virt in the guest, even if available in host CPU

Regards,
Daniel
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Re: [libvirt] [PATCH v1 0/3] libxl: nestedhvm support

Posted by Joao Martins 7 years, 1 month ago

On 03/08/2017 03:07 PM, Daniel P. Berrange wrote:
> On Wed, Mar 08, 2017 at 03:09:11PM +0000, Joao Martins wrote:
>> On 03/08/2017 02:13 PM, Daniel P. Berrange wrote:
>>> On Wed, Mar 08, 2017 at 03:07:12PM +0100, Wim Ten Have wrote:
>>>> From: Wim ten Have <wim.ten.have@oracle.com>
>>>>
>>>> This patch enhances host-passthrough capability to advertise the
>>>> required vendor CPU virtualization feature which will be used to
>>>> enable 'nestedhvm' in the libxl driver.
>>>>
>>>> For Intel virtualization (VT-x)
>>>>     ..
>>>>   <cpu mode='host-passthrough'>
>>>>     <feature policy='require' name='vmx'/>
>>>>   </cpu>
>>>>
>>>> For AMD virtualization (AMD-V)
>>>>     ..
>>>>   <cpu mode='host-passthrough'>
>>>>     <feature policy='require' name='svm'/>
>>>>   </cpu>
>>>
>>> If using host-passthrough or host-model, and the host's CPU includes
>>> vmx or svm, then I would expecte nested-HVM to be enabled, without
>>> needing any extra <feature> flag in the XML. That would match the
>>> semantics used with the QEMU driver.
>>>
>>> The only time we would need to use <feature> is if using mode=custom
>>> along with a named CPU model which lacks vmx/svm flags.
>> Ah OK - I was kinda off unclear on that. So using host-passthrough should be
>> enough then. (while making sure libxl checks if host->cpu does have vmx or svm
>> in its features)
>>
>>> BTW, I wonder how hard it would be to wire up the libxl driver to use
>>> the CPU model infrastructure in src/cpu ? It feels a little odd to use
>>> XML <cpu mode='host-passthrough'/> if we're not then making sure it
>>> actually uses host-passthrough when configuring the guest.
>> While xen libxl do allow to mangle the cpuid, it is meant for disabling features
>> at this point. libxl follows a "host-model" first, meaning the default is to
>> expose as much as features as possible to the guest (depending on whether it's
>> PV or HVM). However, nested virt is a slightly special case since the toolstack
>> will do more than simply unmasking vmx/svm bits (actually within libxl, a sysctl
>> to Xen is performed to enable nested virt to the domain, in which case libxc
>> will handle any vendor specific bits). IOW, even when we improve libxl cpuid
>> policy management to the point we can wire up to libvirt cpu model
>> infrastruture, we would still need to handle the nestedhvm special case (which
>> btw this field would work even for ARM whenever supported).
> 
> Yep, I see. So with libxl using host-model by default, then
> 
>  - If the host CPU includes svm/vmx, turn on nested virt in the guest
>  - Allow use of <feature name="vmx" policy="disable"/> to block nested
>    virt in the guest, even if available in host CPU

Cool, thanks!

Joao

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