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

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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