From e75118a7b581b19b08282c7819c1ec6f68b91b79 Mon Sep 17 00:00:00 2001 From: Suzuki K Poulose 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: # 4.7+ Cc: Will Deacon Cc: James Morse Signed-off-by: Suzuki K Poulose Acked-by: Mark Rutland [catalin.marinas@arm.com: updated code comment] Signed-off-by: Catalin Marinas --- 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 298dd745651e..490db85dec23 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 -- 2.20.1