Re: [Qemu-devel] Re: [PATCH 0/8] kvm: Fixes, cleanups and live migration

[Avi Kivity <avi@redhat.com>]

Gleb Natapov wrote:
> On Sat, May 02, 2009 at 10:12:57PM +0300, Avi Kivity wrote:
>   
>> Gleb Natapov wrote:
>>     
>>>> I think the right thing to do with this is introduce a kvm-cpu savevm 
>>>>  that stores this information since it isn't relevant to TCG.  I 
>>>> think  it's arguable whether you want instruction length there (can 
>>>> you get it  reliably on SVM?).
>>>>
>>>>     
>>>>         
>>> We can't get it on SVM without instruction decoding, but it is not required
>>> on SVM. It is absolutely essential for soft interrupt/exception injection
>>> on VMX and has to be a part of migratable state.
>>>   
>>>       
>> We need it in some neutral form so cross-vendor migration can work.
>>
>>     
> VMX->SVM No problem.
> SVM->VMX bad luck :)  We will have to decode instruction ourself. 
>   

I don't think it's necessary.  We can record the software interrupt at 
the end of the instruction that generated it, and give it higher 
priority than a pending external interrupt.  On vmx, decrement RIP and 
set entry instruction length = 1 before injection.  On svm, use EVENTINJ 
and forget about the instruction length.

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