[PATCH gnupg v11] Disable CPU speculation-related misfeatures

[Steffen Nurpmeso]

Guido Trentalancia via Gnupg-devel wrote in
 <1752063768.6141.10.camel at trentalancia.com>:
 ...
 |common: Disable CPU speculative execution security
 |vulnerabilities[.]
 ...
 | - Flush L1D Cache on context switch out of the
 |   task (use the --enable-l1d-cache-flushing
 |   configure option and "nosmt l1d_flush=on" on the
 |   boot command line to mitigate the vulnerability)

Hm, i turn off SMT like

  # git grep -i smt\/
  bin/system.sh:  [ -n "${SMTCONTROL}" ] && echo off > /sys/devices/system/cpu/smt/control
  bin/zzz.sh:     [ -f /sys/devices/system/cpu/smt/control ] && act 'echo off > /sys/devices/system/cpu/smt/control'

and on the Linux git master branch this seems to work still (i am
on 6.1.*, but i think i use it since 5.10?, or even earlier),
according to

  git show origin/master:Documentation/ABI/testing/sysfs-devices-system-cpu

this should still work out?  Maybe worth noting, at least boot
parameters are well documented...

(Off-topic: i used to temporarily turn it on during compile
sessions, but now am left with

  [ -x /root/bin/cpupower.sh ] && /root/bin/cpupower.sh +
  $time nice -n +19 ${SUPER} -u ports sh -c
  ...

and cpupower.sh no longer deals with SMT at all.  It is off.
But kernel command line is quite heavy (i leave EFI alone if
i can).  Only by updating the kernel series i think the build
time increased by yet another ~25 percent over the last months.)

--steffen
|
|Der Kragenbaer,                The moon bear,
|der holt sich munter           he cheerfully and one by one
|einen nach dem anderen runter  wa.ks himself off
|(By Robert Gernhardt)
|
|During summer's humble, here's David Leonard's grumble
|
|The black bear,          The black bear,
|blithely holds his own   holds himself at leisure
|beating it, up and down  tossing over his ups and downs with pleasure
|
|Farewell, dear collar bear