Re: [Qemu-devel] Re: KQEMU code organization

[Avi Kivity <avi@qumranet.com>]

Jan Kiszka wrote:

  

>> It wouldn't be too bad if you focused on kqemu-user and limited yourself
>> to UP guests.  The first step would be getting the existing KVM support
>> code to function with TCG.  For instance, use TCG to run 16-bit code,
>> and then KVM to run 32/64-bit code.  Once that was all worked out, the
>> rest would be pretty straight-forward porting and code cleanup.
>>     
>
> I guess you mean real-mode code with 16-bit here. /me always wondered
> why it takes an in-kernel code interpreter for kvm to achieve this - at
> least as long as it runs via qemu.
>   

kvm started out with qemu emulating 16-bit code (and before that, even 
32-bit code; kvm only did 64-bit).

The reason I don't like this approach is that it makes the interface 
complex and hard to understand, and makes kvm heavily tied into qemu.

Some problems that arise from having qemu emulate code:
- difficult to do smp properly
- qemu needs to be able to inject mmio for in-kernel emulated devices
- in-kernel devices (lapic, etc.) need to interact with guest code 
executing in userspace



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