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From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Tianyu Lan <Tianyu.Lan@microsoft.com>,
	Konrad Wilk <konrad.wilk@oracle.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Mukesh Ojha <mojha@codeaurora.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Jiri Kosina <jkosina@suse.cz>, Rik van Riel <riel@surriel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Micheal Kelley <michael.h.kelley@microsoft.com>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	Greg KH <gregkh@linuxfoundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Borislav Petkov <bp@alien8.de>,
	x86@kernel.org
Subject: [patch 2/2] x86/smp: Enforce CONFIG_HOTPLUG_CPU when SMP=y
Date: Tue, 26 Mar 2019 17:36:06 +0100
Message-ID: <20190326163811.598166056@linutronix.de> (raw)
In-Reply-To: <20190326163604.348882514@linutronix.de>

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@microsoft.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Konrad Wilk <konrad.wilk@oracle.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Mukesh Ojha <mojha@codeaurora.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Rik van Riel <riel@surriel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Micheal Kelley <michael.h.kelley@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: stable@vger.kernel.org
---
 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.
 
 config HOTPLUG_CPU
-	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.
 
 config BOOTPARAM_HOTPLUG_CPU0
 	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

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