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[Xen-devel] AMD Magny-Cours and HPET


We have had a bug raised against Xen-3.4 that the kexec path fails, on
HP BL465c G7 blades.  The problem does not reproduce on any other AMD
machines I have to hand.

On further investigation, it appears that if the crashing cpu is #0,
then the kexec path hangs forever trying to grab the already locked
legacy_hpet_event.lock in hpet_disable_legacy_broadcast().  Removing the
lock/unlock pair causes the kexec crash path to work as expected.

If the crashing cpu is not #0, then local_time_calibration() gets
worried and dumps the calibration data, and hangs at some later point
which I have yet to find.  This hang happens while performing the NMI
shootdown of other cpus.

The support engineer who raised the bug says that it doesn't occur with
Xen-4.1.  Is there anything architecturally new in the Magny-Cours
processors which might explain this behavior?

I am unwilling to try and backport the hpet code from Xen-4.x without
understanding the problem, although it is a possible solution.


Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900, http://www.citrix.com

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