From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: [PATCH 0/2] Viridian MSRs Date: Tue, 15 Oct 2013 19:12:08 +0100 Message-ID: <1381860730-18191-1-git-send-email-andrew.cooper3@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Xen-devel Cc: Andrew Cooper , Paul Durrant , Keir Fraser , Jan Beulich List-Id: xen-devel@lists.xenproject.org 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 CC: Keir Fraser CC: Jan Beulich -- 1.7.10.4