[Xen-devel] Xen-3.x fix pagefault in cmci handler

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Hello,

XenServer has just had a support escalation, which resulted in this fix.

It appears that certain Intel CPUs (X56xx series) with hyperthreading
enabled have a race condition between an SMI (from the legacy USB
support in this case) and an AP (the other hyperthread) between
SIPI/INIT and trying to execute the first trampoline instruction.

The race condition results in a CMCI complaining about a parity error in
an instruction cache is delivered to Xen as soon as the SMI handler
returns. On Xen-3.x, the CMCI handler dereferences the dom0 pointer,
resulting in a pagefault at this point in boot.

Intel are working to track down why the CMCI is occurring in the first
place, but as it is apparently benign, Xen should continue to boot
regardless.

This error does not affect Xen-4.x, as it correctly checks that the dom0
pointer is not null before trying to use it.

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

Attachment: cmci-fix-pagefault.patch
Description: Text Data

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