K 10
svn:author
V 3
kib
K 8
svn:date
V 27
2018-01-31T14:36:27.338768Z
K 7
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V 674
IBRS support, AKA Spectre hardware mitigation.

It is coded according to the Intel document 336996-001, reading of the
patches posted on lkml, and some additional consultations with Intel.

For existing processors, you need a microcode update which adds IBRS
CPU features, and to manually enable it by setting the tunable/sysctl
hw.ibrs_disable to 0.  Current status can be checked in sysctl
hw.ibrs_active.  The mitigation might be inactive if the CPU feature
is not patched in, or if CPU reports that IBRS use is not required, by
IA32_ARCH_CAP_IBRS_ALL bit.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D14029

END