From: Andi Kleen <ak@suse.de>
To: virtualization@lists.osdl.org
Subject: Re: [RFC, PATCH 17/24] i386 Vmi msr patch
Date: Tue, 14 Mar 2006 17:23:53 +0100
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Cc: Zachary Amsden <zach@vmware.com>, Linus Torvalds <torvalds@osdl.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Xen-devel <xen-devel@lists.xensource.com>,
       Andrew Morton <akpm@osdl.org>, Dan Hecht <dhecht@vmware.com>,
       Dan Arai <arai@vmware.com>, Anne Holler <anne@vmware.com>,
       Pratap Subrahmanyam <pratap@vmware.com>,
       Christopher Li <chrisl@vmware.com>, Joshua LeVasseur <jtl@ira.uka.de>,
       Chris Wright <chrisw@osdl.org>, Rik Van Riel <riel@redhat.com>,
       Jyothy Reddy <jreddy@vmware.com>, Jack Lo <jlo@vmware.com>,
       Kip Macy <kmacy@fsmware.com>, Jan Beulich <jbeulich@novell.com>,
       Ky Srinivasan <ksrinivasan@novell.com>,
       Wim Coekaerts <wim.coekaerts@oracle.com>,
       Leendert van Doorn <leendert@watson.ibm.com>
References: <200603131812.k2DICGJE005747@zach-dev.vmware.com>
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On Monday 13 March 2006 19:12, Zachary Amsden wrote:
> Fairly straightforward code motion of MSR / TSC / PMC accessors
> to the sub-arch level.  Note that rdmsr/wrmsr_safe functions are
> not moved; Linux relies on the fault behavior here in the event
> that certain MSRs are not supported on hardware, and combining
> this with a VMI wrapper is overly complicated.  The instructions
> are virtualizable with trap and emulate, not on critical code
> paths, and only used as part of the MSR /proc device, which is
> highly sketchy to use inside a virtual machine, but must be
> allowed as part of the compile, since it is useful on native.

I'm not aware of any MSR access being on a critical code
path on a 32bit kernel. 

And I don't think it's a good idea to virtualize the TSC 
without CPU support.

Why would you want to do any of this?

-Andi
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