linux-kernel - Re: [PATCH] riscv: force __cpu_up_ variables to put in data section

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Date:   Thu, 30 Apr 2020 11:22:59 -0700
From:   Atish Patra <atishp@...shpatra.org>
To:     Zong Li <zong.li@...ive.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] riscv: force __cpu_up_ variables to put in data section

On Thu, Apr 30, 2020 at 2:53 AM Zong Li <zong.li@...ive.com> wrote:
>
> Put __cpu_up_stack_pointer and __cpu_up_task_pointer in data section.
> Currently, these two variables are put in bss section, there is a
> potential risk that secondary harts get the uninitialized value before
> main hart finishing the bss clearing. In this case, all secondary
> harts would go through the waiting loop and enable the MMU before
> main hart set up the page table.
>

That would be only true if you are using random booting protocol with
SBI v0.1 implementation.
With HSM extension in place, all the secondary cores are waiting in
firmware. The booting core
will bring them up one by one from cpu_up method.

The HSM extension is already available in OpenSBI v0.7 and Linux
kernel 5.7-rc1 onwards.

> Signed-off-by: Zong Li <zong.li@...ive.com>
> ---
>  arch/riscv/kernel/cpu_ops.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/kernel/cpu_ops.c b/arch/riscv/kernel/cpu_ops.c
> index c4c33bf02369..0ec22354018c 100644
> --- a/arch/riscv/kernel/cpu_ops.c
> +++ b/arch/riscv/kernel/cpu_ops.c
> @@ -15,8 +15,8 @@
>
>  const struct cpu_operations *cpu_ops[NR_CPUS] __ro_after_init;
>
> -void *__cpu_up_stack_pointer[NR_CPUS];
> -void *__cpu_up_task_pointer[NR_CPUS];
> +void *__cpu_up_stack_pointer[NR_CPUS] __section(.data);
> +void *__cpu_up_task_pointer[NR_CPUS] __section(.data);
>
>  extern const struct cpu_operations cpu_ops_sbi;
>  extern const struct cpu_operations cpu_ops_spinwait;
> --
> 2.26.1
>
>


-- 
Regards,
Atish