Re: [patch 2/2] x86/smp: Enforce CONFIG_HOTPLUG_CPU when SMP=y

[Greg KH]

On Tue, Mar 26, 2019 at 05:36:06PM +0100, Thomas Gleixner wrote:
> The SMT disable 'nosmt' command line argument is not working properly when
> CONFIG_HOTPLUG_CPU is disabled. The teardown of the sibling CPUs which are
> required to be brought up due to the MCE issues, cannot work. The CPUs are
> then kept in a half dead state.
> 
> As the 'nosmt' functionality has become popular due to the speculative
> hardware vulnerabilities, the half torn down state is not a proper solution
> to the problem.
> 
> Enforce CONFIG_HOTPLUG_CPU=y when SMP is enabled so the full operation is
> possible.
> 
> Reported-by: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Konrad Wilk <konrad.wilk@xxxxxxxxxx>
> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> Cc: Mukesh Ojha <mojha@xxxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Jiri Kosina <jkosina@xxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Micheal Kelley <michael.h.kelley@xxxxxxxxxxxxx>
> Cc: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
> Cc: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
>  arch/x86/Kconfig |    8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)

Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>