x86 instruction emulation in hvm

[Emre Can Sezer <ecsezer@ncsu.edu>]

I'm running an HVM guest using shadow page tables on a 64bit machine.  
I'm working on a project where I mark certain pages read-only and 
capture the writes into these pages.  I then try to emulate the write 
instructions using x86_emulate as is done in arch/x86/mm/shadow/multi.c.

The instruction I'm trying to emulate is:
asm("mov %%gs,%0" : "=m" (p->thread.gsindex));

Since the source operand is a segment register, and the x86_emulate_ops 
structure that is being used does not have a ops->read_segment function 
defined, the emulation fails.

Is there an easy way to add or activate this functionality?  Perhaps a 
full emulator, since one would expect to see other cases of memory 
writes that are not handled as well.

Thanks,

John