Re: [kvm-devel] Real Mode Improvement on Intel Hosts - GSoC Project

[Avi K. <av...@qu...>]

Mohammed Gamal wrote:
>>  Why do that unconditionally, instead of only when in a big-real-mode state?
>>     
>
> Is big-real-mode the only state where we have problems?
>   

In general, we need to emulate whenever we are in a VT-unfriendly state, 
where that is defined as guest state that fails the guest state checks 
defined by section 22.3.1 of volume 3B of the Intel software development 
manual, "checks on the guest state area", when that state is legal in a 
real processor.  To date, we have encountered only two instances of such 
VT-unfriendly states:

- "big real mode", where segment limits are not exactly 0xffff
- protected mode transitions, where cs.rpl !=ss.rpl for a brief while

There may well be more, as we remove the various hacks currently in 
place, and as we expand the envelope to support hybrid 16/32 bit guests 
like Windows 3.1 and Windows 95.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.