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
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