Re: binary drivers and development

John Richard Moser
2005-03-13T05:00:45Z

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You wanna give me a quick run-down on x86 of CPL and Ring levels? It's
been bugging me. I know they're there and have a basic idea that they
control what a context can do, don't know what CPL stands for, and
there's a visible gap in my knowledge. I like to understand everything,
it makes things easier.

Felipe Alfaro Solana wrote:
> On Thu, 10 Mar 2005 17:32:39 -0500, John Richard Moser
> <nigelenki@comcast.net> wrote:
>
>>CPL=3 scares me; context switches are expensive. can they have direct
>>hardware access? I'm sure a security model to isolate user mode drivers
>>could be in place. . .
>>
>>. . . huh. Xen seems to run Linux at CPL=3 and give direct hardware
>>access, so I guess user mode drivers are possible *shrug*. Linux isn't
>>a microkernel though.
>
>
> Xen hypervisor runs at Ring0, while the guest OSs it supports run at Ring1.
>

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