linux-kernel - Re: arch/riscv: disable too many harts before pick main boot hart

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Date:   Fri, 13 Sep 2019 12:04:32 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     merle@...denedlinux.org
CC:     Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        citypw@...denedlinux.org
Subject:     Re: arch/riscv: disable too many harts before pick main boot hart

On Thu, 05 Sep 2019 23:51:15 PDT (-0700), merle@...denedlinux.org wrote:
> From 12300865d1103618c9d4c375f7d7fbe601b6618c Mon Sep 17 00:00:00 2001
> From: Xiang Wang <merle@...denedlinux.org>
> Date: Fri, 6 Sep 2019 11:56:09 +0800
> Subject: [PATCH] arch/riscv: disable too many harts before pick main boot hart
>
> These harts with id greater than or equal to CONFIG_NR_CPUS need to be disabled.
> But pick the main Hart can choose any one. So, before pick the main hart, you
> need to disable the hart with id greater than or equal to CONFIG_NR_CPUS.
>
> Signed-off-by: Xiang Wang <merle@...denedlinux.org>
> ---
> arch/riscv/kernel/head.S | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index 0f1ba17e476f..cfffea38eb17 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -63,6 +63,11 @@ _start_kernel:
> li t0, SR_FS
> csrc sstatus, t0
>
> +#ifdef CONFIG_SMP
> + li t0, CONFIG_NR_CPUS
> + bgeu a0, t0, .Lsecondary_park
> +#endif
> +
> /* Pick one hart to run the main boot sequence */
> la a3, hart_lottery
> li a2, 1
> @@ -154,9 +159,6 @@ relocate:
>
> .Lsecondary_start:
> #ifdef CONFIG_SMP
> - li a1, CONFIG_NR_CPUS
> - bgeu a0, a1, .Lsecondary_park
> -
> /* Set trap vector to spin forever to help debug */
> la a3, .Lsecondary_park
> csrw CSR_STVEC, a3

It would be better to decouple the hart masks from NR_CPUS, as there's really 
no reason for these to be the same.

Reviewed-by: Palmer Dabbelt <palmer@...ive.com>