LKML Archive on
 help / color / Atom feed
From: Thomas Gleixner <>
To: LKML <>
Cc: Tianyu Lan <>,
	Konrad Wilk <>,
	Josh Poimboeuf <>,
	Mukesh Ojha <>,
	Peter Zijlstra <>,
	Jiri Kosina <>, Rik van Riel <>,
	Andy Lutomirski <>,
	Micheal Kelley <>,
	"K. Y. Srinivasan" <>,
	Greg KH <>,
	Linus Torvalds <>,
	Borislav Petkov <>,
Subject: [patch 2/2] x86/smp: Enforce CONFIG_HOTPLUG_CPU when SMP=y
Date: Tue, 26 Mar 2019 17:36:06 +0100
Message-ID: <> (raw)
In-Reply-To: <>

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

Reported-by: Tianyu Lan <>
Signed-off-by: Thomas Gleixner <>
Cc: Konrad Wilk <>
Cc: Josh Poimboeuf <>
Cc: Mukesh Ojha <>
Cc: Peter Zijlstra <>
Cc: Jiri Kosina <>
Cc: Rik van Riel <>
Cc: Andy Lutomirski <>
Cc: Micheal Kelley <>
Cc: K. Y. Srinivasan <>
Cc: Greg KH <>
Cc: Linus Torvalds <>
Cc: Borislav Petkov <>
 arch/x86/Kconfig |    8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2217,14 +2217,8 @@ config RANDOMIZE_MEMORY_PHYSICAL_PADDING
 	   If unsure, leave at the default value.
-	bool "Support for hot-pluggable CPUs"
+	def_bool y
 	depends on SMP
-	---help---
-	  Say Y here to allow turning CPUs off and on. CPUs can be
-	  controlled through /sys/devices/system/cpu.
-	  ( Note: power management support will enable this option
-	    automatically on SMP systems. )
-	  Say N if you want to disable CPU hotplug.
 	bool "Set default setting of cpu0_hotpluggable"

  parent reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-26 16:36 [patch 0/2] cpu/hotplug: Prevent damage with SMP=y and HOTPLUG_CPU=n Thomas Gleixner
2019-03-26 16:36 ` [patch 1/2] cpu/hotplug: Prevent crash when CPU bringup fails on CONFIG_HOTPLUG_CPU=n Thomas Gleixner
2019-03-27  1:12   ` Greg KH
2019-03-28 12:38   ` [tip:smp/urgent] " tip-bot for Thomas Gleixner
2019-03-26 16:36 ` Thomas Gleixner [this message]
2019-03-27  1:12   ` [patch 2/2] x86/smp: Enforce CONFIG_HOTPLUG_CPU when SMP=y Greg KH
2019-03-28 12:39   ` [tip:smp/urgent] " tip-bot for Thomas Gleixner

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on

Archives are clonable:
	git clone --mirror lkml/git/0.git
	git clone --mirror lkml/git/1.git
	git clone --mirror lkml/git/2.git
	git clone --mirror lkml/git/3.git
	git clone --mirror lkml/git/4.git
	git clone --mirror lkml/git/5.git
	git clone --mirror lkml/git/6.git
	git clone --mirror lkml/git/7.git
	git clone --mirror lkml/git/8.git
	git clone --mirror lkml/git/9.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ \
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:

AGPL code for this site: git clone