linux-kernel - Re: [PATCH v3 2/3] RISC-V: Implement nosmp commandline option.

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Date:   Mon, 29 Apr 2019 16:50:03 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     atish.patra@....com
CC:     linux-kernel@...r.kernel.org, atish.patra@....com,
        aou@...s.berkeley.edu, schwab@...e.de, anup@...infault.org,
        dmitriy@...-tech.org, johan@...nel.org,
        linux-riscv@...ts.infradead.org,
        Paul Walmsley <paul.walmsley@...ive.com>, tglx@...utronix.de,
        Christoph Hellwig <hch@...radead.org>
Subject:     Re: [PATCH v3 2/3] RISC-V: Implement nosmp commandline option.

On Tue, 23 Apr 2019 17:02:26 PDT (-0700), atish.patra@....com wrote:
> nosmp command line option sets max_cpus to zero. No secondary harts
> will boot if this is enabled. But present cpu mask will still point to
> all possible masks.
>
> Fix present cpu mask for nosmp usecase.
>
> Signed-off-by: Atish Patra <atish.patra@....com>
> ---
>  arch/riscv/kernel/smpboot.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> index eb533b5c2c8c..a8ad200581aa 100644
> --- a/arch/riscv/kernel/smpboot.c
> +++ b/arch/riscv/kernel/smpboot.c
> @@ -47,6 +47,17 @@ void __init smp_prepare_boot_cpu(void)
>
>  void __init smp_prepare_cpus(unsigned int max_cpus)
>  {
> +	int cpuid;
> +
> +	/* This covers non-smp usecase mandated by "nosmp" option */
> +	if (max_cpus == 0)
> +		return;
> +
> +	for_each_possible_cpu(cpuid) {
> +		if (cpuid == smp_processor_id())
> +			continue;
> +		set_cpu_present(cpuid, true);
> +	}
>  }
>
>  void __init setup_smp(void)
> @@ -74,7 +85,6 @@ void __init setup_smp(void)
>
>  		cpuid_to_hartid_map(cpuid) = hart;
>  		set_cpu_possible(cpuid, true);
> -		set_cpu_present(cpuid, true);
>  		cpuid++;
>  	}

Thanks.  I've taken all three of these into for-next.