RE: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V

[KY Srinivasan]

> -----Original Message-----
> From: devel [mailto:devel-bounces@xxxxxxxxxxxxxxxxxxxxxx] On Behalf Of KY
> Srinivasan
> Sent: Thursday, April 18, 2013 9:23 AM
> To: Michael S. Tsirkin
> Cc: olaf@xxxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx; jasowang@xxxxxxxxxx;
> x86@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; bp@xxxxxxxxx; Jan Beulich;
> hpa@xxxxxxxxx; apw@xxxxxxxxxxxxx; devel@xxxxxxxxxxxxxxxxxxxxxx;
> tglx@xxxxxxxxxxxxx
> Subject: RE: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V
> 
> 
> 
> > -----Original Message-----
> > From: Michael S. Tsirkin [mailto:mst@xxxxxxxxxx]
> > Sent: Thursday, April 18, 2013 3:48 AM
> > To: KY Srinivasan
> > Cc: Jan Beulich; olaf@xxxxxxxxx; bp@xxxxxxxxx; apw@xxxxxxxxxxxxx;
> > x86@xxxxxxxxxx; tglx@xxxxxxxxxxxxx; devel@xxxxxxxxxxxxxxxxxxxxxx;
> > gregkh@xxxxxxxxxxxxxxxxxxx; jasowang@xxxxxxxxxx; linux-
> > kernel@xxxxxxxxxxxxxxx; hpa@xxxxxxxxx
> > Subject: Re: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V
> >
> > On Wed, Apr 17, 2013 at 04:28:36PM +0000, KY Srinivasan wrote:
> > >
> > >
> > > > -----Original Message-----
> > > > From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> > > > Sent: Wednesday, April 17, 2013 11:51 AM
> > > > To: KY Srinivasan; Michael S. Tsirkin
> > > > Cc: olaf@xxxxxxxxx; bp@xxxxxxxxx; apw@xxxxxxxxxxxxx; x86@xxxxxxxxxx;
> > > > tglx@xxxxxxxxxxxxx; devel@xxxxxxxxxxxxxxxxxxxxxx;
> > gregkh@xxxxxxxxxxxxxxxxxxx;
> > > > jasowang@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; hpa@xxxxxxxxx
> > > > Subject: RE: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-
> V
> > > >
> > > > >>> On 17.04.13 at 17:31, KY Srinivasan <kys@xxxxxxxxxxxxx> wrote:
> > > > > If Xen were to change where it would not unconditionally emulate Hyper-
> V,
> > I
> > > > > would not be opposed to taking
> > > > > this check out.
> > > >
> > > > But it doesn't do this unconditionally, only upon admin request.
> > >
> > > >From the discussion we had a couple of months ago, the default setting was
> to
> > enable
> > > Hyper-V emulation for all guests. If this is not the case, we ought to be able to
> > drop this.
> > > However, I think it is not reasonable to add additional checks (in addition to
> > hypervisor check)
> > > to customize the run-time in the guest for the specific Hypervisor.
> > >
> > > Regards,
> > >
> > > K. Y
> >
> > Parse error. What are you trying to say? I'm just saying it's best to do
> > things in the way that make it possible for Xen to implement hyperv in a
> > more complete way in the future and have things just work
> > and in a way that does not change guest/hypervisor interface.
> 
> There is no error to parse here. I need to setup the vmbus interrupt before I
> can contact the host. As I said I am fine with dropping this check if Xen behavior is
> changed appropriately. We have a mechanism for hypervisor detection and a
> mechanism for discovering features within a hypervisor. Once we confirm the
> existence of a specific hypervisor, we ought to be able to do what is needed for
> that hypervisor (unless the hypervisor feature flag precludes it) without having to
> go through hoops to discover if we are in a hypervisor emulation mode where
> the emulation
> may not be complete. In this particular case, the need for VMBUS related
> infrastructure cannot be
> currently determined via the feature detection mechanism.
> 
> For features that cannot be detected via CPUID feature bits, we can use some
> other CPUID based
> mechanism to discriminate. For instance in the case under discussion, I could
> install
> hyperv_callback_vector only if we are on an environment that supports the
> vmbus infrastructure.
> Unfortunately there is no positive test for this. The best we can do is a negative
> test. I could move the
> Xen check and conditionally install the hyperv_callback vector.

Michael,

I think I can address the problem you have raised. I will send a patch out soon.

Regards,

K. Y
> 
> Regards,
> 
> K. Y
> 
> 
> >
> > > >
> > > > Jan
> > > >
> > > >
> > >
> >
> 
> 
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