linux-kernel - [PATCH] [4.7] arm64: Honor nosmp kernel command line option

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Date:	Thu, 21 Jul 2016 11:15:27 +0100
From:	Suzuki K Poulose <suzuki.poulose@....com>
To:	catalin.marinas@....com
Cc:	will.deacon@....com, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Mark Rutland <mark.rutland@....com>,
	James Morse <james.morse@....com>
Subject: [PATCH] [4.7] arm64: Honor nosmp kernel command line option

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.

Fixes: commit 44dbcc93ab67145 ("arm64: Fix behavior of maxcpus=N")
Cc: Will Deacon <will.deacon@....com>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Mark Rutland <mark.rutland@....com>
Cc: James Morse <james.morse@....com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
---
 arch/arm64/kernel/smp.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index d242e81..ec08b7a 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -694,6 +694,13 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
 	smp_store_cpu_info(smp_processor_id());
 
 	/*
+	 * If UP is mandated by "nosmp"(implies maxcpus=0), don't bother about
+	 * secondary CPUs.
+	 */
+	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.
-- 
2.7.4