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

From: Suzuki K Poulose
Date: Thu Jul 21 2016 - 06:15:46 EST

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@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: James Morse <james.morse@xxxxxxx>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
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)

+ * 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.