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[Xen-devel] [PATCH 0/2] Viridian MSRs

This set of two patches advertises 3 constant, read-only MSRs of timing
information to a viridian capable VM.

There is an as-yet-unidentified issue when running Windows 8.1 / Server 2012r2
under Xen where it will periodically (1 in 10 attempt) appear to fall into an
idle loop rather than schedule userspace processes (such as failing to run a
login session).

I am still investigating the underlying cause.  One possibility is an
interaction of TSC time calibration interacting poorly with the Xen scheduler.

Unfortunately, attempting to divine what windows is unhappy about with its
environment is rather tricky (even a BSOD would be more useful than the
current symptoms), but providing these MSRs causes Windows to prefer rdtsc
over the HPET main counter as a source of time, and 'fixes' the above issue.

CC: Paul Durrant <paul.durrant@xxxxxxxxxx>
CC: Keir Fraser <keir@xxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>


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