Make it possible to re-evaluate cpu_features.

Add cpuctl(4) ioctl CPUCTL_EVAL_CPU_FEATURES which forces re-read of
cpu_features, cpu_features2, cpu_stdext_features, and
std_stdext_features2.

The intent is to allow the kernel to see the changes in the CPU
features after micocode update.  Of course, the update is not atomic
across variables and not synchronized with readers.  See the man page
warning as well.

Reviewed by:	imp (previous version), jilles
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D13770

1 files changed, 26 insertions, 7 deletions

diff --git a/usr.sbin/cpucontrol/cpucontrol.8 b/usr.sbin/cpucontrol/cpucontrol.8
index 2a1a5f109901..4e54bb51bafc 100644
--- a/usr.sbin/cpucontrol/cpucontrol.8
+++ b/usr.sbin/cpucontrol/cpucontrol.8
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd September 30, 2017
+.Dd January 5, 2018
 .Dt CPUCONTROL 8
 .Os
 .Sh NAME
@@ -34,46 +34,51 @@
 device
 .Sh SYNOPSIS
 .Nm
+.Bk
 .Op Fl v
 .Fl m Ar msr
-.Bk
 .Ar device
 .Ek
+.Bk
 .Nm
 .Op Fl v
 .Fl m Ar msr Ns = Ns Ar value
-.Bk
 .Ar device
 .Ek
+.Bk
 .Nm
 .Op Fl v
 .Fl m Ar msr Ns &= Ns Ar mask
-.Bk
 .Ar device
 .Ek
+.Bk
 .Nm
 .Op Fl v
 .Fl m Ar msr Ns |= Ns Ar mask
-.Bk
 .Ar device
 .Ek
+.Bk
 .Nm
 .Op Fl v
 .Fl i Ar level
-.Bk
 .Ar device
 .Ek
+.Bk
 .Nm
 .Op Fl v
 .Fl i Ar level,level_type
-.Bk
 .Ar device
 .Ek
+.Bk
 .Nm
 .Op Fl vn
 .Op Fl d Ar datadir
 .Fl u
+.Ar device
+.Ek
 .Bk
+.Nm
+.Fl e
 .Ar device
 .Ek
 .Sh DESCRIPTION
@@ -136,6 +141,20 @@ The
 .Nm
 utility will walk through the configured data directories
 and apply all firmware updates available for this CPU.
+.It Fl e
+Re-evaluate the kernel flags indicating the present CPU features.
+This command is typically executed after a firmware update was applied
+which changes information reported by the
+.Dv CPUID
+instruction.
+.Pp
+.Bf -symbolic
+Only execute the
+.Fl e
+command after the microcode update was applied to all CPUs in the system.
+The kernel does not operate correctly if the features of processors are
+not identical.
+.Ef
 .It Fl v
 Increase the verbosity level.
 .It Fl h