4.4-stable review patch. If anyone has any objections, please let me know.
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From: Thomas Gleixner tglx@linutronix.de
commit bebd024e4815b1a170fcd21ead9c2222b23ce9e6 upstream.
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 Acked-by: Greg Kroah-Hartman gregkh@linuxfoundation.org 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: Linus Torvalds torvalds@linux-foundation.org Cc: Borislav Petkov bp@alien8.de Cc: K. Y. Srinivasan kys@microsoft.com Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20190326163811.598166056@linutronix.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/Kconfig | 8 +------- 1 file changed, 1 insertion(+), 7 deletions(-)
--- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -1970,14 +1970,8 @@ config PHYSICAL_ALIGN Don't change this unless you know what you are doing.
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"