Re: [Xen-devel] [PATCH] This patch fixes several issues related to vmxassist

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 31 Mar 2006, at 12:06, Li, Xin B wrote:

> > I don't know the heritage of that code. I expect someone
> > decided it was
> > good enough to be getting on with but maybe now it is time to revisit
> > and see if we can implement a watertight version which correctly uses
> > hidden segment descriptor state which is readily available
> > when running
> > on VMX.
> My patch just enhanced the current implementation, and actually it
> breaks windows, but I have a updated version in hand, and tests show
> that all the combinations is OK till now.
>
> In my mind, the correct way is to identify whether a cpu is in big real
> mode, but seems this is a little bit hard to do.
Well, it's impossible to know for certain without looking at hidden 
descriptor state isn't it. Big real mode is only possible because the 
hidden state can be out of sync with the current execution mode.
If that state can be made available to the address() function then it's 
implementation, and confidence in its correctness, becomes trivial. Do 
we have that state available directly in the guest at that point? Or 
would we need to grab the state from Xen?
 -- Keir


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