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

[Anthony Liguori <anthony@codemonkey.ws>]

Gleb Natapov wrote:
> On Fri, May 01, 2009 at 05:40:00PM -0500, Anthony Liguori wrote:
>   
>> Jan Kiszka wrote:
>>     
>>> Besides refreshed versions of my already posted fixes and cleanups for
>>> KVM, this series comes with patches to enable live migration in KVM
>>> mode. If there is still some migration bit missing compared to qemu-kvm,
>>> please let me know.
>>>   
>>>       
>> In qemu-kvm, we also save:
>>
>> MSR_IA32_TSC
>> mp_state
>> interrupt_bitmap
>>
>> In QEMU, we probably should just emulate MSR_IA32_TSC and then we can  
>> reuse that for save/restore.
>>
>> interrupt_bitmap is a bit more tricky.  It only ever can have one bit  
>> set AFAICT but I don't see anything that we're currently saving that  
>> maps to it which leads me to wonder why KVM needs it and QEMU doesn't.
>>
>>     
> KVM stores pending interrupt there (interrupt that is not in irq chip
> already but not yet injected to vcpu). I have patch (not yet submitted)
> that removes the use of interrupt_bitmap from kernel. It recreated only
> for migration bits. My plan is to change migration bits too, but it is
> trickier if we want to keep backwards compatibility. No need to
> introduce interrupt_bitmap in qemu upstream IMO. We need to migrate
> pending interrupt though. The info that should be migrated it interrupt
> vector, interrupt type (soft/hw) and instruction length (needed for
> injection of soft interrupts on VMX).
>   

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?).

If we did that, v1 could be interrupt_bitmap and then v2 can be this new 
data layout.

Regards,

Anthony Liguori

> --
> 			Gleb.
>
>
>