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    SubjectRe: Hyper-Threading Vulnerability
    On Fri, May 13, 2005 at 02:26:20PM -0700, Andy Isaacson wrote:
    > On Fri, May 13, 2005 at 09:05:49PM +0200, Andi Kleen wrote:
    > > On Fri, May 13, 2005 at 02:38:03PM -0400, Richard F. Rebel wrote:
    > > > Why? It's certainly reasonable to disable it for the time being and
    > > > even prudent to do so.
    > >
    > > No, i strongly disagree on that. The reasonable thing to do is
    > > to fix the crypto code which has this vulnerability, not break
    > > a useful performance enhancement for everybody else.
    > Pardon me for saying so, but that's bullshit. You're asking the crypto
    > guys to give up a 5x performance gain (that's my wild guess) by giving
    > up all their data-dependent algorithms and contorting their code wildly,
    > to avoid a microarchitectural problem with Intel's HT implementation.

    And what you're doing is to ask all the non crypto guys to give
    up an useful optimization just to fix a problem in the crypto guy's
    code. The cache line information leak is just a information leak
    bug in the crypto code, not a general problem.

    There is much more non crypto code than crypto code around - you
    are proposing to screw the majority of codes to solve a relatively
    obscure problem of only a few functions, which seems like the totally
    wrong approach to me.

    BTW the crypto guys are always free to check for hyperthreading
    themselves and use different functions. However there is a catch
    there - the modern dual core processors which actually have
    separated L1 and L2 caches set these too to stay compatible
    with old code and license managers.

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