Re: KVM & VMX root mode

Sander van Leeuwen
2007-09-03T08:09:04Z

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Avi Kivity wrote:
> Sander van Leeuwen wrote:
>
>> You are mistaken. VT-x allows multiple clients to work concurrently.
>> There's only one catch: all those
>> clients should follow certain guidelines.
>>
>
> Currently, kvm assumes that it is the only user that issues vmptrld
> instructions. There may me other such assumptions in the code.
>
> There is also the question of who issues the vmxon/vmxoff instructions
> and set the magic msr bits that enable kvm. You can't have two
> hypervisors doing that; that would be racy. It should be possible to
> abstract those bits out to something outside kvm, but I don't see that
> happening.
>
>
VirtualBox currently always executes vmxon when it wants to execute some
guest code. When leaving
ring 0 it issues the corresponding vmxoff. While that may increase world
switch overhead, it has not turned
out to be an issue for us. I think it's a bit risky to use somebody
else's vmxon pointer.

You have a point with the msr updates though.

--
Kind regards / mit freundlichen Gruessen / Met vriendelijke groet
Sander van Leeuwen

innoTek GmbH
http://www.innotek.de
Germany

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