* [PATCH] [4.7] arm64: Honor nosmp kernel command line option
@ 2016-07-21 10:15 Suzuki K Poulose
2016-07-21 10:36 ` Mark Rutland
2016-07-21 15:05 ` Catalin Marinas
0 siblings, 2 replies; 3+ messages in thread
From: Suzuki K Poulose @ 2016-07-21 10:15 UTC (permalink / raw)
To: linux-arm-kernel
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@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: James Morse <james.morse@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@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 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
^ permalink raw reply related [flat|nested] 3+ messages in thread
* [PATCH] [4.7] arm64: Honor nosmp kernel command line option
2016-07-21 10:15 [PATCH] [4.7] arm64: Honor nosmp kernel command line option Suzuki K Poulose
@ 2016-07-21 10:36 ` Mark Rutland
2016-07-21 15:05 ` Catalin Marinas
1 sibling, 0 replies; 3+ messages in thread
From: Mark Rutland @ 2016-07-21 10:36 UTC (permalink / raw)
To: linux-arm-kernel
On Thu, Jul 21, 2016 at 11:15:27AM +0100, Suzuki K Poulose wrote:
> 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@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: James Morse <james.morse@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@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 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
Nit: missing space between the quote abnd opening bracket. It would also
be nicer to have s/implies/which implies/
Otherwise:
Acked-by: Mark Rutland <mark.rutland@arm.com>
Mark.
> + * 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
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* [PATCH] [4.7] arm64: Honor nosmp kernel command line option
2016-07-21 10:15 [PATCH] [4.7] arm64: Honor nosmp kernel command line option Suzuki K Poulose
2016-07-21 10:36 ` Mark Rutland
@ 2016-07-21 15:05 ` Catalin Marinas
1 sibling, 0 replies; 3+ messages in thread
From: Catalin Marinas @ 2016-07-21 15:05 UTC (permalink / raw)
To: linux-arm-kernel
On Thu, Jul 21, 2016 at 11:15:27AM +0100, Suzuki K. Poulose wrote:
> 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@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: James Morse <james.morse@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Queued for 4.8, with Mark's comment and a cc stable for 4.7
--
Catalin
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