From e75118a7b581b19b08282c7819c1ec6f68b91b79 Mon Sep 17 00:00:00 2001
From: Suzuki K Poulose <suzuki.poulose@arm.com>
Date: Thu, 21 Jul 2016 11:15:27 +0100
Subject: [PATCH] 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: 44dbcc93ab67 ("arm64: Fix behavior of maxcpus=N")
Cc: <stable@vger.kernel.org> # 4.7+
Cc: Will Deacon <will.deacon@arm.com>
Cc: James Morse <james.morse@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
[catalin.marinas@arm.com: updated code comment]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.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 298dd745651eb..490db85dec23b 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -692,6 +692,13 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
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
--
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