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[Xen-devel] Re: [RFC, PATCH 17/24] i386 Vmi msr patch
- To: virtualization@xxxxxxxxxxxxxx
- From: Andi Kleen <ak@xxxxxxx>
- Date: Tue, 14 Mar 2006 17:23:53 +0100
- Cc: Zachary Amsden <zach@xxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Pratap Subrahmanyam <pratap@xxxxxxxxxx>, Wim Coekaerts <wim.coekaerts@xxxxxxxxxx>, Joshua LeVasseur <jtl@xxxxxxxxxx>, Dan Hecht <dhecht@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Jack Lo <jlo@xxxxxxxxxx>, Christopher Li <chrisl@xxxxxxxxxx>, Chris Wright <chrisw@xxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxx>, Anne Holler <anne@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxxxx>, Jyothy Reddy <jreddy@xxxxxxxxxx>, Kip Macy <kmacy@xxxxxxxxxxx>, Ky Srinivasan <ksrinivasan@xxxxxxxxxx>, Leendert van Doorn <leendert@xxxxxxxxxxxxxx>, Dan Arai <arai@xxxxxxxxxx>
- Delivery-date: Wed, 15 Mar 2006 10:14:32 +0000
- List-id: Xen developer discussion <xen-devel.lists.xensource.com>
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?
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