Re: [Xen-devel] Re: Regression in 3.1 causes Xen to use wrong idle routine

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Nov 14, 2011 at 01:19:01PM -0500, Konrad Rzeszutek Wilk wrote:
> On Sun, Nov 13, 2011 at 04:59:10PM +0000, Keir Fraser wrote:
> > On 13/11/2011 03:46, "Len Brown" <lenb@xxxxxxxxxx> wrote:
> > 
> > >> The problem I see is that select_idle_routine() is called from
> > >> arch/x86/kernel/cpu/common.c and since Xen setup does not set pm_idle
> > >> anymore, it can cause mwait_idle or amd_e400_idle functions to be 
> > >> selected.
> > >> In testing it seem amd_e400_idle in PVM domU at least does not 
> > >> immediately
> > >> cause
> > >> problems, but mwait_idle just causes crashes. From the reports I have
> > >> this may be related to older hypervisors (3.1 and older) not clearing the
> > >> mwait
> > >> capability. But overall there seems something wrong in the interaction.
> > > 
> > > Why is Xen advertising X86_FEATURE_MWAIT and then crashing
> > > when the dom0 (or other guests) use what it advertises?
> > > 
> > > What versions of Xen have this bug?
> > 
> > Xen doesn't advertise MWAIT. Possibly Xen-pv_ops is lying to the rest of the
> > kernel via the cpuid pv_ops hook. This would probably be because Xen is
> 
> I can't seem to find anything in there advertising the MWAIT feature.
> 
> > relying on the OSPM in dom0 kernel to parse out Cx/Px info which Xen itself
> > *can* use.
> 
> The Cx/Px patches that would parse the Cx/Px and then percolate those up
> to the hypervisor are in mainline. So that is not it.

<sigh> I meant to say "are _not_ in mainline". Sorry for the confusion.

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