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Re: [Xen-devel] PC8 Residency on Broadwell hardware

On Sep 12, 2016, at 2:00 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:

On 12.09.16 at 10:47, <andrew.cooper3@xxxxxxxxxx> wrote:
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).

Where did you find the info? I think you are talking about MSR_PKG_C8_RESIDENCY (630H).

The SDM says (35.13):

"Processors with signatures 06_3DH and 06_47H support the MSR interfaces listed in Table 35-18, Table 35-19, Table 35-20, Table 35-23, Table 35-27, Table 35-28, Table 35-32, and Table 35-33.”

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.

And indeed I had requested this same information already well over
a week ago, without having heard back.

Sorry, it seems that the email was buried in the pile of the emails that I received while I was in Toronto.


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