Re: [Qemu-devel] POLL: Why do you use kqemu?

[Avi Kivity <avi@redhat.com>]

Jamie Lokier wrote:
>>> Plus kvm's not suitable for some guests.  I'm thinking old Windows
>>> guests with 16-bit kernel code here.
>>>  
>>>       
>> kvm on amd will run these perfectly.
>>     
>
> So the "Guest Support Status" prominently on the front page of
> linux-kvm.org is wrong for current versions?  It specifically mentions
> AMD hosts.
>
> (I notice AMD KVM != Intel KVM hasn't factored into this discussion yet...)
>
> Guest           KVM tested             Host CPU/bits    Result
> ----------------------------------------------------------------
> Windows 98SE 	kvm-63                 Intel 32         Fails
> Windows 98SE 	kvm-80, 2.6.27.7       AMD 64           no way
> Windows 95 	kvm-44, 2.6.23-rc8     AMD 64, 32 	no way
>   

Well, maybe there's some other bug in there.  But kvm-amd 16 bit support 
is as good as the native cpu's.  kvm-intel with the new 'unrestricted 
guest' should be the same.

>>> It has come up before that kvm will eventually support 16-bit code
>>> better, although I got the impression that it would never support full
>>> 16-bit virtualisation accurately, so e.g. Windows 95 will not run on
>>> it, nor some other partially 16-bit OSes.  Possibly not even very old
>>> versions of Linux, I'm not sure.
>>>
>>> Don't ask me _why_ I want to run them. :-)
>>>
>>> Just a data point that it's not just about the host hardware, and as
>>> far as I know kqemu can accelerate them.
>>>  
>>>       
>> It falls back to qemu for 16-bit code.
>>     
>
> I was under the impression it was planned to remove TCG support when
> using KVM.  If not, fine, it's ok for 16-bit code to run in TCG and
> probably better than vm86 or the in-kernel interpreter.
>   

vm86 doesn't work on x86_64.  kvm will run most 16-bit code natively, 
just have to complete task switch support and fix any bugs.

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