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SubjectRe: [patch 2/2] x86 amd fix cmpxchg read acquire barrier
* Ingo Molnar (mingo@elte.hu) wrote:
>
> * Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> wrote:
>
> > " // Opteron Rev E has a bug in which on very rare occasions a locked
> > // instruction doesn't act as a read-acquire barrier if followed by a
> > // non-locked read-modify-write instruction. Rev F has this bug in
> > // pre-release versions, but not in versions released to customers,
> > // so we test only for Rev E, which is family 15, model 32..63 inclusive.
>
> Dunno. The fix looks a bit intrusive (emits a NOP even on good
> CPUs). Also, the text above says "not in versions released to
> customers".
>
> So unless there's an official erratum or reports in the field (not
> from early prototype systems shipped to developers) i'd not rush to
> apply it, just yet.
>

Actually, Operon Rev E has this bug in the field (family 15, model
32..64). Rev F only had the bug in pre-releases.

But yes, it's bad that it drags so many code additions to something as
critical as cmpxchg. I start to think it might be better to just
disallow bringing up more than one CPU on these machines.

Mathieu

> Ingo

--
Mathieu Desnoyers
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