[Xen-devel] PC8 Residency on Broadwell hardware

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Hello,

c/s 350bc1a9d4 "x86: support newer Intel CPU models" changed the set of
MSRs read by Xeon Broadwell hardware (specifically, model 79 / 0x47).

Rereading the manual, it does indeed indicate that this MSR is available.

However, experimentally it is not.  All Broadwell hardware XenServer has
(both SDPs and production systems) reliably take a #GP fault when trying
to read this MSR.  Haswell hardware appears fine (and indeed, was
reading that MSR before).

Intel: Please can you confirm whether the documentation is correct?  If
it is, do you have any idea why the MSR might not be available?  I can't
spot anything relevant in the platform errata documents.

Thanks,

~Andrew

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