xen 4.15.5: msr_relaxed required for MSR 0x1a2

[James Dingwall <james-xen@xxxxxxxxxxxxxx>]

Hi,

Per the msr_relaxed documentation:

   "If using this option is necessary to fix an issue, please report a bug."

After recently upgrading an environment from Xen 4.14.5 to Xen 4.15.5 we
started experiencing a BSOD at boot with one of our Windows guests.  We found
that enabling `msr_relaxed = 1` in the guest configuration has resolved the
problem.  With a debug build of Xen and `hvm_debug=2048` on the command line
the following messages were caught as the BSOD happened:

(XEN) [HVM:11.0] <vmx_msr_read_intercept> ecx=0x1a2
(XEN) vmx.c:3298:d11v0 RDMSR 0x000001a2 unimplemented
(XEN) d11v0 VIRIDIAN CRASH: 1e ffffffffc0000096 fffff80b8de81eb5 0 0

I found that MSR 0x1a2 is MSR_TEMPERATURE_TARGET and from that this patch
series from last month:

https://patchwork.kernel.org/project/xen-devel/list/?series=796550

Picking out just a small part of that fixes the problem for us. Although the
the patch is against 4.15.5 I think it would be relevant to more recent
releases too.

Thanks,
James

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