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

From: Ian Rogers
Subject: Re: [Qemu-devel] QVM86, SKAS.. many modules, one vision?
Date: Mon, 09 May 2005 13:59:00 +0100
User-agent: Mozilla Thunderbird 0.8 (X11/20040913)

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.


Ian Rogers

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