Message-ID: <4233C912.80706@comcast.net>
Date: Sun, 13 Mar 2005 00:01:06 -0500
From: John Richard Moser <nigelenki@comcast.net>
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To: Felipe Alfaro Solana <felipe.alfaro@gmail.com>
CC: Peter Chubb <peter@chubb.wattle.id.au>, linux-kernel@vger.kernel.org
Subject: Re: binary drivers and development
References: <423075B7.5080004@comcast.net> <423082BF.6060007@comcast.net>	 <16944.49977.715895.8761@wombat.chubb.wattle.id.au>	 <4230CB07.3020904@comcast.net> <6f6293f105031207535938c687@mail.gmail.com>
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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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