Enabling MCA causes system hangs

Andriy Gapon avg at freebsd.org
Fri Sep 10 14:32:09 UTC 2010

on 10/09/2010 10:28 Andriy Gapon said the following:
> on 10/09/2010 05:36 Daniel O'Connor said the following:
>> Hi, I recently tried enabling MCA (ie w.mca.enabled=1 in loader.conf) on an
>> 8.0-STABLE system and found that it would cause the system to hang after a
>> few minutes of uptime.
>> The screen would go black and the monitor would turn off (regardless of
>> wether it was in X or not) and only a hard reset would bring it back.
>> Also I found that quite often I had to power cycle the whole PC or the BIOS
>> wouldn't detect the hard disks on boot(!) after a hang.
>> uname is.. FreeBSD midget.dons.net.au 8.0-STABLE FreeBSD 8.0-STABLE #6
>> r202903M: Sun Jan 24 13:45:11 CST 2010
>> darius at midget.dons.net.au:/usr/obj/usr/src/sys/MIDGET  amd64

Oh, I should have payed attention to the version.
I think that this is a known and resolved problem.
There is a hardware bug in AMD 10h processors that is triggered by combination
of enabled MCA and FreeBSD superpages.
So, you either have to disable one of them or upgrade to a more recent version.
The version you need is r206183.  The latest stable/8 would do, obviously.

>> The motherboard is a Gigabyte GA-MA785GM-US2H with an Athlon II X2 240 CPU &
>> 4Gb of RAM.
> Do you also have superpages enabled (vm.pmap.pg_ps_enabled)?
> If so, please try to turn them off and report back if that helps.

Andriy Gapon

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