initial commit

LICENSE

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+smtCtrl
+===
+Copyright (c) 2018, Bret R. Human
+All rights reserved.
+
+Further documentation can be found at
+   https://psi.cynicaloptimist.me/Caffarius/smtCtrl/
+Happy modding! -Bret
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+1. Redistributions of source code must retain the above copyright notice,
+   the documentation link and note, this list of conditions, and the following
+   disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright notice,
+   this list of conditions and the following disclaimer in the documentation
+   and/or other materials provided with the distribution.
+
+3. All advertising materials mentioning features or use of this
+   software must display the following acknowledgment:
+"Built using software developed by Cynical Optimist - https://cynicaloptimist.me
+ Ask what we can build for you at info@cynicaloptimist.me"
+
+4. The names "Cynical Optimist" and "Bret R. Human" and the software name listed
+   at the top of this document, or the domain "cynicaloptimist.me" or any
+   affiliated service must not be used to endorse or promote products derived
+   from this software without prior written permission. For written permission,
+   contact info@cynicaloptimist.me.
+
+5. Products derived from this software may not be called the software name
+   listed at the top of this document nor may "Cynical Optimist" or the software
+   name listed at the top of this document appear in their names without prior
+   written permission of Bret R. Human.
+
+6. Redistributions of any form whatsoever must retain the following
+   acknowledgment:
+"Built using software developed by Cynical Optimist - https://cynicaloptimist.me
+ Ask what we can build for you at info@cynicaloptimist.me"
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

README.md

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+# smtCtrl
+
+Script that can enable/disable SMT at will on Ryzen systems. Includes optional systemd service to disable SMT before multi-user.target.
+
+Ad astra per aspera, security experts.

disable-smt.service

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+[Unit]
+Description=Disable Simultaneous Multithreading
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+
+ExecStart=/root/.script/smt.sh disable
+ExecStop=/root/.script/smt.sh status
+
+[Install]
+WantedBy=multi-user.target

smt.sh

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+#!/bin/bash
+## Copyright © 2018 Bret Human
+## https://cynicaloptimist.me/
+##
+##    Documentation at:
+## https://mage.cynicaloptimist.me/en/smtCtrl
+## https://psi.cynicaloptimist.me/Caffarius/smtCtrl
+##
+## For questions or comments write:
+##    info@cynicaloptimist.me
+#
+# Try your best to control SMT on Ryzen CPUs.
+# Usage: ./smt.sh (enable|disable|status)
+
+num_cores=`lscpu | grep "CPU(s):" | grep -v "," | grep -v "-" | cut -d: -f2 | awk '{print $1}'`
+num_procs=`nproc`
+
+disable() {
+   if [ "${num_procs}" -lt "${num_cores}" ]; then
+      echo "SMT has already been disabled!"
+   else
+      echo -n "Disabling SMT: "
+      i="1"
+      while [ "${i}" -lt "${num_cores}" ]; do
+         echo "0" > /sys/devices/system/cpu/cpu${i}/online
+         i=$[ $i + 2 ]
+      done
+      unset i
+      echo "Done."
+      return 0
+   fi
+   return 1
+}
+
+enable() {
+   if [ "${num_procs}" -eq "${num_cores}" ]; then
+      echo "SMT has already been enabled!"
+   else
+      echo -n "Enabling SMT: "
+      i="1"
+      while [ "${i}" -lt "${num_cores}" ]; do
+         echo "1" > /sys/devices/system/cpu/cpu${i}/online
+         i=$[ $i + 2 ]
+      done
+      unset i
+      echo "Done."
+      return 0
+   fi
+   return 1
+}
+
+status() {
+   cat /proc/cpuinfo |egrep "processor|physical id|core id" | sed 's/^processor/\nprocessor/g'
+}
+
+case "$1" in
+   disable)
+      disable
+      ;;
+   enable)
+      enable
+      ;;
+   status)
+      status
+      ;;
+   *)
+      echo "   Usage: ./smt.sh (disable | enable | status)"
+      ;;
+esac