Re: [Qemu-devel] QVM86, SKAS.. many modules, one vision?

[Ian Rogers]

Paul Brook wrote:

> For user-mode emulation the largest chunk of address space is the translated 
> code buffer. This needs to be able to directly address the guest memory 
> space, so sharing a VM with the host qemu process isn't really a problem. We 
> just map the host qemu out of the way somewhere. This is different from 
> native UML where with SKAS you can run applications without any foreign areas 
> mapped into the guest address space.
>  
Yup, but if you are emulating more than just a user process (ie a whole 
OS), or you can't guarantee the security of the user process (ie it 
could go messing with the translation cache), then just mapping things 
elsewhere is just adopting the ostrich position. Multi-segments are an 
obvious way to solve this but currently there's little support in the 
OS. modify_ldt works quite well, you can hide the translation cache 
below it, but it means you can't map pages at the end of the address 
space. That's why some module support would be good.

Regards,

Ian Rogers