Comment 680 for bug 1690085

(In reply to Moritz Naumann from comment #592)
> The latest firmware for X370 Taichi, v5.50 (2019/4/24), removes the "Power
> Supply Idle Control" option off the configuration UI; downgrading is not
> supported (but effectively possible at least from Windows). It is still
> possible to set "Power Supply Idle Control" (C6 package) via MSR using e.g.
> /sbin/modprobe msr && /usr/sbin/wrmsr -a 0xC0010292 true
> during boot.
>
> Luckily, this workaround may no longer be needed. While, with default 'BIOS'
> (actually UEFI firmware) settings on v5.50, Linux 4.18 still freezes during
> idle for me, it no longer does so on 5.1.2 (apparently - needs more testing
> - not on 5.0 either).

Since 5.0.10, and this commit ...:

(https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.0.10)
"commit 205c53cbe553c9e5a9fe93f63e398da7e59124b6
Author: Thomas Gleixner <email address hidden>
Date: Sun Apr 14 19:51:06 2019 +0200

    x86/speculation: Prevent deadlock on ssb_state::lock

    commit 2f5fb19341883bb6e37da351bc3700489d8506a7 upstream.

    Mikhail reported a lockdep splat related to the AMD specific ssb_state
    lock:

      CPU0 CPU1
      lock(&st->lock);
                                 local_irq_disable();
                                 lock(&(&sighand->siglock)->rlock);
                                 lock(&st->lock);
      <Interrupt>
         lock(&(&sighand->siglock)->rlock);

      *** DEADLOCK ***

    The connection between sighand->siglock and st->lock comes through seccomp,
    which takes st->lock while holding sighand->siglock.

    Make sure interrupts are disabled when __speculation_ctrl_update() is
    invoked via prctl() -> speculation_ctrl_update(). Add a lockdep assert to
    catch future offenders.

    Fixes: 1f50ddb4f418 ("x86/speculation: Handle HT correctly on AMD")"

... the problem seems to be fixed! I no longer need to use idle=halt and the systems don't freeze anymore!