Opteron rev E family of processor expose a bug where, in very rare

ocassions, memory barriers semantic is not honoured by the hardware
itself. As a result, some random breakage can happen in uninvestigable
ways (for further explanation see at the content of the commit itself).

As long as just a specific familly is bugged of an entire architecture
is broken, a complete fix-up is impratical without harming to some
extents the other correct cases.
Considering that (and considering the frequency of the bug exposure)
just print out a warning message if the affected machine is identified.

Pointed out by:	Samy Al Bahra <sbahra at repnop dot org>
Help on wordings by:	jeff
MFC:	3 days

1 files changed, 18 insertions, 0 deletions

diff --git a/sys/i386/i386/identcpu.c b/sys/i386/i386/identcpu.c
index 66c5fed..e8210c2 100644
--- a/sys/i386/i386/identcpu.c
+++ b/sys/i386/i386/identcpu.c
@@ -1303,6 +1303,24 @@ print_AMD_info(void)
 			    (amd_whcr & 0x0100) ? "Enable" : "Disable");
 		}
 	}
+
+	/*
+	 * Opteron Rev E shows a bug as in very rare occasions a read memory
+	 * barrier is not performed as expected if it is followed by a
+	 * non-atomic read-modify-write instruction.
+	 * As long as that bug pops up very rarely (intensive machine usage
+	 * on other operating systems generally generates one unexplainable
+	 * crash any 2 months) and as long as a model specific fix would be
+	 * impratical at this stage, print out a warning string if the broken
+	 * model and family are identified.
+	 */
+	if (CPUID_TO_FAMILY(cpu_id) == 0xf && CPUID_TO_MODEL(cpu_id) >= 0x20 &&
+	    CPUID_TO_MODEL(cpu_id) <= 0x3f) {
+		printf("WARNING: This architecture revision has known SMP "
+		    "hardware bugs which may cause random instability\n");
+		printf("WARNING: For details see: "
+		    "http://bugzilla.kernel.org/show_bug.cgi?id=11305\n");
+	}
 }
 
 static void