linux-kernel - Re: [patch 2/2] x86/smp: Enforce CONFIG_HOTPLUG

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Message-ID: <20190327011251.GB3099@kroah.com>
Date:   Wed, 27 Mar 2019 10:12:51 +0900
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        Konrad Wilk <konrad.wilk@...cle.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Mukesh Ojha <mojha@...eaurora.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Kosina <jkosina@...e.cz>, Rik van Riel <riel@...riel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Micheal Kelley <michael.h.kelley@...rosoft.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org
Subject: Re: [patch 2/2] x86/smp: Enforce CONFIG_HOTPLUG_CPU when SMP=y

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@...rosoft.com>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: Konrad Wilk <konrad.wilk@...cle.com>
> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> Cc: Mukesh Ojha <mojha@...eaurora.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Jiri Kosina <jkosina@...e.cz>
> Cc: Rik van Riel <riel@...riel.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Micheal Kelley <michael.h.kelley@...rosoft.com>
> Cc: K. Y. Srinivasan <kys@...rosoft.com>
> Cc: Greg KH <gregkh@...uxfoundation.org>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: stable@...r.kernel.org
> ---
>  arch/x86/Kconfig |    8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)

Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>