On Sun, Nov 13, 2011 at 04:59:10PM +0000, Keir Fraser wrote:

On 13/11/2011 03:46, "Len Brown" [off-list ref] wrote:

quoted

quoted

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.