linux-kernel - Re: Opteron Rev E has a bug ... a locked instruction doesn't act as a read-acquire barrier

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Date:	Mon, 4 Aug 2008 15:26:11 +0200
From:	Mikael Pettersson <mikpe@...uu.se>
To:	Arkadiusz Miskiewicz <arekm@...en.pl>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Opteron Rev E has a bug ... a locked  instruction doesn't act as a read-acquire barrier

Arkadiusz Miskiewicz writes:
 > 
 > Hello,
 > 
 > http://google-perftools.googlecode.com/svn-history/r48/trunk/src/base/atomicops-internals-x86.cc
 > says
 > 
 > "  // 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.
 >   if (strcmp(vendor, "AuthenticAMD") == 0 &&       // AMD
 >       family == 15 &&
 >       32 <= model && model <= 63) {
 >     AtomicOps_Internalx86CPUFeatures.has_amd_lock_mb_bug = true;
 >   } else {
 >     AtomicOps_Internalx86CPUFeatures.has_amd_lock_mb_bug = false;
 >   }
 > "
 > 
 > does kernel have quirk/workaround for this? I'm looking at arch/x86/kernel/cpu 
 > but I don't see workaround related to this (possibly I'm overlooking).

I can find no reference to this alleged RevE erratum in the
Athlon64/Opteron revision guide (25759.pdf).

But if this bug is real then we need to know about it. Could
you ask the author of the code you quoted above to clarify?

/Mikael
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