RE: [Xen-devel] FXSAVE instruction emulation

["Su, Disheng" <disheng.su@xxxxxxxxx>]

Abhinav Srivastava wrote:
> Hi there,
> 
> I am using Xen-3.2 on Intel-VT hardware. My guest VM is running Linux
> kernel 2.6.21 in HVM mode. 
> 
> I was trying to do some emulation from the hypervisor and my code was
> failing to emulate FXSAVE instructions. I looked on the mailing list
> and found the following patch that does that:  
> 
> "[Xen-devel] [PATCH 2/4] Enable VirtualPC 2007 run on top of XEN:
> fxsave" from [Su, Disheng] 
> 
> However, when I applied this patch it is still not working. I am
> going to the default case of this patch that directly calls "goto
> cannot_emulate". When I printed the instruction it is like this: 0f
> ae e8. The value of modrm_reg that patch uses to check which case
> statement to execute is 05. The patch only handles the value 0.   
> 
"0f ae e8" is the lfence instruction. It isn't handled in this patch...
You can refer to Intel Software Developer Manual Vol.2B A.4.2 for detail
information.
> Could some explain what does this mean? And, how to solve this
> problem? 
>
Don't why you need to emulate this instruction...
Do you want to emulate instructions step by step?
How about bypass this "lfence"?
> Any help would be appreciated.
> 
> Thanks,
> Abhinav
> 
> 
> 
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Best Regards,
Disheng, Su

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