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arm64: Honor nosmp kernel command line option

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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 44dbcc93ab ("arm64: Fix behavior of maxcpus=N") fixed the
behavior for maxcpus >= 1, but broke maxcpus = 0.

Fixes: 44dbcc93ab ("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>
This commit is contained in:
Suzuki K Poulose 2016-07-21 11:15:27 +01:00 committed by Catalin Marinas
parent 9113c2aa05
commit e75118a7b5
1 changed files with 7 additions and 0 deletions
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7
arch/arm64/kernel/smp.c
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@ -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