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[Xen-devel] RE: Solaris and PVRDTSCP

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] RE: Solaris and PVRDTSCP
From: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
Date: Fri, 1 Jul 2011 20:32:08 +0100
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Thread-topic: Solaris and PVRDTSCP
> -----Original Message-----
> From: Dan Magenheimer [mailto:dan.magenheimer@xxxxxxxxxx]
> Sent: 01 July 2011 18:51
> To: Paul Durrant; xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: RE: Solaris and PVRDTSCP
> Hi Paul --
> > From: Paul Durrant [mailto:Paul.Durrant@xxxxxxxxxx]
> > Cc: Dan Magenheimer
> > Subject: Solaris and PVRDTSCP
> >
> > Hi,
> >
> >   I've been trying to figure out why my copy of s10u9 did not run
> PV
> > drivers when I installed it on Xen 4.1 when it was perfectly happy
> on Xen 3.4...
> >
> >   It turns out that the kernel is making a check that the maximal
> Xen
> > CPUID leaf is no greater than base + 2. This was true on Xen 3.4
> but
> > when the PVRDTSCP patch was added it ceased to be true with the
> addition of the cpuid_time_leaf code.
> What happens?  Belly up?  Why is this only on PV drivers rather than
> pure HVM?

No, it doesn't go belly up, You just don't get PV drivers, you get emulated 
instead. As for why the check is there? No idea.

> >   Clearly future versions of the Solaris kernel should revise this
> > check but to allow this kernel to enable PV drivers I was
> wondering
> > what sort of workaround could be done. My current thoughts are
> along the lines of disabling the extra CPUID leaf if tsc_mode is <
> This seems reasonable.  The info on that leaf could be useful in
> other modes, but likely hasn't been.
> > An alternative might
> > be to introduce another tsc_mode that specifically causes the leaf
> to be obscured. Thoughts?
> >
> >   Paul

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