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Re: [Qemu-devel] Re: backdoor

From: Lluís
Subject: Re: [Qemu-devel] Re: backdoor
Date: Tue, 26 Oct 2010 00:48:37 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.50 (gnu/linux)

Anthony Liguori writes:

> On 10/25/2010 08:37 AM, Lluís wrote:
>> I know extending the ISA is not nice at all, but I think that's much
>> more maintainable than a per-guest OS interface (supposing some will
>> need extra guest drivers).

> On x86, there are some architecturally nicer ways to do this.

> For instance, a CPUID leaf could be used in the 0x40001xxx range.

Right, I commented this in a previous mail as a much nicer way to do it,
but I was just too lazy to look up how CPUID works and instead ported
the implementation I already had in bochs :)

Although I can port it to CPUID if people find it useful to have
upstream. I just need a way to provide an immediate and a register-based
argument (at the same time), which does not require executing more than
a couple of extra instructions (right now everything fits on a single

Being able te receive back information would be a plus, which I think
CPUID already does to return its results; although I think the ISA says
that _all_ registers are "used" after executing it.


 "And it's much the same thing with knowledge, for whenever you learn
 something new, the whole world becomes that much richer."
 -- The Princess of Pure Reason, as told by Norton Juster in The Phantom

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