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Date:      Mon, 16 May 2005 18:00:31 +1000
From:      Peter Jeremy <peterjeremy@optushome.com.au>
To:        Nate Lawson <nate@root.org>
Cc:        Colin Percival <cperciva@freebsd.org>
Subject:   Re: cvs commit: src/sys/amd64/amd64 mp_machdep.csrc/sys/amd64/include cpufunc.h src/sys/i386/i386 mp_machdep.c src/sys/i386/include cpufunc.h
Message-ID:  <20050516080031.GD34537@server.vk2pj.dyndns.org>
In-Reply-To: <4287AD84.6070600@root.org>
References:  <97079.1116154766@critter.freebsd.dk> <4287AD84.6070600@root.org>

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On Sun, May 15, 2005 at 01:13:56PM -0700, Nate Lawson wrote:
>My point was that FreeBSD (like most general-purpose OS) has many timing 
>channels that are comparably as effective for an attacker as HTT. 

If you take the bandwidth of the timing channel into account, I don't
believe there are any other timing channels that come anywhere near the
HTT attack.  Maybe Colin has a better idea of what other timing channels
exist and how they compare to HTT.

>Disabling HTT does not significantly reduce an attacker's likelihood of 
>success since they can just use another timing channel.  However, it 
>does disable a useful feature.  Are we going to disable SMP next?

How useful is HTT on FreeBSD?  FreeBSD does not have a HTT-aware
scheduler at present and I don't believe there are even any plans to
make either scheduler HTT-aware.  Without this, you only gain a benefit
if you are running fairly specific workloads.

Peter



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