[libvirt] [PATCH 1/2] conf: add crash to hyperv features

[Daniel P. Berrange]

On Wed, Nov 11, 2015 at 12:09:33PM +0300, Denis V. Lunev wrote:
> On 11/11/2015 11:57 AM, Dmitry Andreev wrote:
> >Adding colleague to CC
> >
> >On 11.11.2015 11:34, Jiri Denemark wrote:
> >>On Wed, Nov 11, 2015 at 08:34:02 +0100, Peter Krempa wrote:
> >>>On Thu, Nov 05, 2015 at 16:54:02 +0300, Dmitry Andreev wrote:
> >>>>
> >>>>On 05.11.2015 14:06, Jiri Denemark wrote:
> >>>>>On Mon, Oct 26, 2015 at 13:23:32 +0300, Dmitry Andreev wrote:
> >>>>>>Add crash CPU feature for Hyper-V. Hyper-V crash MSR's can be used
> >>>>>>by Hyper-V based guests to notify about occurred guest crash.
> >>>>>>
> >>>>>>XML:
> >>>>>><features>
> >>>>>>    <hyperv>
> >>>>>>      <crash state='on'/>
> >>>>>>    </hyperv>
> >>>>>></features>
> >>>>>Sounds like this is related to an existing panic device we already
> >>>>>support. So what does enabling hv_crash do in QEMU? Is it an
> >>>>>additional
> >>>>>channel to a panic device or is the panic device still needed even if
> >>>>>hv_crash is enabled? In any case, I think we should map this
> >>>>>somehow to
> >>>>>the panic device instead of copying 1:1 the way QEMU enables
> >>>>>hv_crash.
> >>>>pvpanic and Hyper-V crash are independent ways for guest to notify
> >>>>about
> >>>>OS crash. Both ways rise the 'qemu guest panicked' event. Domain can
> >>>>have both hv_crash and pvpanic enabled at the same time.
> >>>>
> >>>>pvpanic is in <devices> section in domain configuration because it
> >>>>is an
> >>>>ISA device. Hyper-V crash is a hypervisor's feature, which enables a
> >>>>set
> >>>>of model-specific registers. Guest can use this registers to send
> >>>>notification and store additional information about a crash. This is a
> >>>>part of Microsoft hypervisor interface.
> >>>Device or not, I don't really like having two distinct places to
> >>>configure similar functionality.
> >>>
> >>><device>
> >>>   <panic model='hyperv'/>
> >>>
> >>>will do just fine IMO.
> >>Yeah, this what I was thinking about. After all, we already do something
> >>similar on Power. The guest panic notification is an integral part of
> >>the platform itself so there's no device we need to add. To reflect this
> >>in our domain XMLs, we just always add
> >>
> >>     <device>
> >>       <panic/>
> >>     </device>
> >>
> >>Thus using <panic> element for hv_crash seems like the best approach to
> >>me. We'd have just one place for configuring all kinds of guest crash
> >>notifications. The question is what the XML should look like. The form
> >>suggested by Peter looks good, but then we should probably add the model
> >>attribute to all panic devices to make it consistent. So a theoretical
> >>XML using all currently supported panic "devices" would be:
> >>
> >>     <device>
> >>       <panic model='hyperv'/>  <!-- hv_crash -->
> >>       <panic model='isa'/>     <!-- pvpanic -->
> >>       <panic model='pseries'/> <!-- Power -->
> >>     </device>
> >>
> >>'pseries' model would only be allowed on Power, while the others would
> >>only be allowed on x86. We'd need to automatically add model='...' to
> >>existing device, but it should be pretty easy. Any older libvirt would
> >>just ignore the attribute completely and a new libvirt would add
> >>model='isa' on x86 and model='pseries' on Power.
> >>
> >>Jirka
> >>
> QEMU accepts this option through HyperV set of CPU options.
> In QEMU this declared as follows:
> 
> static Property x86_cpu_properties[] = {
>     DEFINE_PROP_BOOL("pmu", X86CPU, enable_pmu, false),
>     { .name  = "hv-spinlocks", .info  = &qdev_prop_spinlocks },
>     DEFINE_PROP_BOOL("hv-relaxed", X86CPU, hyperv_relaxed_timing, false),
>     DEFINE_PROP_BOOL("hv-vapic", X86CPU, hyperv_vapic, false),
>     DEFINE_PROP_BOOL("hv-time", X86CPU, hyperv_time, false),
>     DEFINE_PROP_BOOL("hv-crash", X86CPU, hyperv_crash, false),
>     DEFINE_PROP_BOOL("hv-reset", X86CPU, hyperv_reset, false),
>     DEFINE_PROP_BOOL("hv-vpindex", X86CPU, hyperv_vpindex, false),
>     DEFINE_PROP_BOOL("hv-runtime", X86CPU, hyperv_runtime, false),
>     DEFINE_PROP_BOOL("check", X86CPU, check_cpuid, true),
>     DEFINE_PROP_BOOL("enforce", X86CPU, enforce_cpuid, false),
>     DEFINE_PROP_BOOL("kvm", X86CPU, expose_kvm, true),
>     DEFINE_PROP_UINT32("level", X86CPU, env.cpuid_level, 0),
>     DEFINE_PROP_UINT32("xlevel", X86CPU, env.cpuid_xlevel, 0),
>     DEFINE_PROP_UINT32("xlevel2", X86CPU, env.cpuid_xlevel2, 0),
>     DEFINE_PROP_STRING("hv-vendor-id", X86CPU, hyperv_vendor_id),
>     DEFINE_PROP_END_OF_LIST()
> };
> 
> Thus your proposal means that in this case we will have to add
> this option to CPU part of the command line from devices
> part.
> 
> Is this correct?
> 
> That is why we proposing to follow this way and keep HyperV
> CPU properties in one place.
> 
> And, finally, 'no', this is not a device from QEMU perspective
> of view.

Having libvirt model XML in exactly the same way as QEMU models
its command line is an explicit *non-goal* of libvirt.

Libvirt aims to provide an XML representation that is generic
across arbitrary hypervisor platforms. So it is fully expected
that we will model things differently from QEMU in some cases
where there is a better way todo things from the libvirt POV.

All that matters is that the approach we choose in libvirt
is sufficiently expressive to cover the range of features of
the underlying platforms.


Regards,
Daniel
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