Re: [PATCH][RFC] Emulating real mode with x86_emulate

[Anthony Liguori <aliguori@us.ibm.com>]

Kamble, Nitin A wrote:
> On Fri, 2007-03-30 at 15:11 -0700, Anthony Liguori wrote:
>
>> set_cr0 is returning 1 though which should increment eip to the next
>> instruction.
>>
>> I'm a bit perplexed about my eip now and also why your eip is still 0. 
>> It should be the instruction following the mov cr0.
>>
>> Regards,
>>
>> Anthony Liguori
>>
>
> Hi Anthony,
>     I don't see any code doing context save/restore like 
> vmx_world_save , vmx_world_restore in the current code for the 
> hyperviser based emulator.

Before calling x86_emulate, we use hvm_store_cpu_guest_regs() to copy 
the guest state into a regs struct (which happens to be the vcpu's reg 
struct).  This reads directly from the VMCS via vmread() so it should be 
okay.  I don't think a vmx_world_save/restore is actually needed 
although perhaps I'm missing something?

> Also the function  arch_vmx_do_resume() is called at the time of vcpu 
> schedule, so it is not right to call the  vmx_do_emulate() from there.

Right, the idea was to have x86_emulate() be called instead of 
vmentry().  I thought that being in the set_cr0 path would ensure that 
we go through do_resume() again.  Is this assumption incorrect?

I didn't want to just stick it in the set_cr0 path because we ought to 
be able to pull the emulation loop into common code for SVM/VT and the 
do_resume path seems like the only place where there's common place to 
hook right now.

Regards,

Anthony Liguori

> The code would need vmx_world_save/restore in the code path before 
> returning to vmx_asm_vmexit_handler from vmx_vmexit_handler.
> Without that I don't see it can emulate any instructions.
>
> Thanks & Regards,
> Nitin
> Open Source Technology Center, Intel Corporation.
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