MULX on haswell triggers ILLOP

Torbjorn Granlund tg at
Wed Oct 23 00:07:46 UTC 2013

I have an Intel Haswell system which runs Xen/NetBSD with Debian 7.2,
NetBSD 6.1.2 and FreeBSD 9.2 guests.

The FreeBSD guest casts an ILLOP when fed with the new MULX instruction.
This is a plain integer register based instruction which should require
zero kernel support.

MULX is part of the BMI2 extensions.

The instruction works fine in the other guest systems.

What is going on?  How can FreeBSD reject this instruction?

I have not tried to run FreeBSD on the bare metal, so I cannot tell if
BMI2 works as expected there.


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