Patch "arm64: Honor nosmp kernel command line option" has been added to the 4.7-stable tree

This is a note to let you know that I've just added the patch titled

arm64: Honor nosmp kernel command line option

to the 4.7-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
arm64-honor-nosmp-kernel-command-line-option.patch
and it can be found in the queue-4.7 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Suzuki K Poulose <[email protected]>
Date: Thu, 21 Jul 2016 11:15:27 +0100
Subject: arm64: Honor nosmp kernel command line option

From: Suzuki K Poulose <[email protected]>

commit e75118a7b581b19b08282c7819c1ec6f68b91b79 upstream.

Passing "nosmp" should boot the kernel with a single processor, without provision to enable secondary CPUs even if they are present. "nosmp" is implemented by setting maxcpus=0. At the moment we still mark the secondary CPUs present even with nosmp, which allows the userspace to bring them up. This patch corrects the smp_prepare_cpus() to honor the maxcpus == 0.

Commit 44dbcc93ab67145 ("arm64: Fix behavior of maxcpus=N") fixed the behavior for maxcpus >= 1, but broke maxcpus = 0.

---
 arch/arm64/kernel/smp.c |    7 +++++++
 1 file changed, 7 insertions(+)

@@ -693,6 +693,13 @@ void __init smp_prepare_cpus(unsigned in
 	smp_store_cpu_info(smp_processor_id());
 
 	/*
+	 * If UP is mandated by "nosmp" (which implies "maxcpus=0"), don't set
+	 * secondary CPUs present.
+	 */
+	if (max_cpus == 0)
+		return;
+
+	/*
 	 * Initialise the present map (which describes the set of CPUs
 	 * actually populated at the present time) and release the
 	 * secondaries from the bootloader.

Patches currently in stable-queue which might be from [email protected] are

queue-4.7/arm64-fix-incorrect-per-cpu-usage-for-boot-cpu.patch queue-4.7/arm64-honor-nosmp-kernel-command-line-option.patch