linux-kernel - Re: [PATCH 2/2] riscv: provide default implementations for __sbi_set_timer and __sbi_send_ipi

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Message-ID: <CAOnJCULdeHn4GmrP8PLsWS43g=HYjUwiA2txisEqgzSmuCoA7w@mail.gmail.com>
Date:   Mon, 13 Dec 2021 18:10:21 -0800
From:   Atish Patra <atishp@...shpatra.org>
To:     Heiko Stuebner <heiko@...ech.de>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup@...infault.org>,
        Jisheng Zhang <jszhang@...nel.org>,
        Christoph Müllner <christoph.muellner@...ll.eu>,
        Philipp Tomsich <philipp.tomsich@...ll.eu>,
        Nick Kossifidis <mick@....forth.gr>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] riscv: provide default implementations for
 __sbi_set_timer and __sbi_send_ipi

On Mon, Dec 13, 2021 at 3:21 AM Heiko Stuebner <heiko@...ech.de> wrote:
>
> The mentioned function pointers get called from different sbi functions
> which may get called from other areas of the kernel without fully
> checking if the sbi initialization was done.

SBI initialization happens in sbi_init which is called from setup_arch.
setup_smp happens after that. Thus, there won't be an IPI issued
before SMP is set up.

For __sbi_set_timer, the first time it will be called from this path.
time_init->timer_probe->riscv_timer_init_dt

time_init is called from start_kernel after setup_arch. In fact,
setup_arch is called very early
in the start_kernel.

Is there any other scenario where these SBI functions can be invoked
before SBI is initialized ?

>
> So similarly to sbi_remote_fence_i, provide empty functions for them
> to prevent any null-pointer dereferences in the future.
>
> Signed-off-by: Heiko Stuebner <heiko@...ech.de>
> ---
>  arch/riscv/kernel/sbi.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
> index 69d0a96b97d0..6a21345c6712 100644
> --- a/arch/riscv/kernel/sbi.c
> +++ b/arch/riscv/kernel/sbi.c
> @@ -14,6 +14,13 @@
>  unsigned long sbi_spec_version __ro_after_init = SBI_SPEC_VERSION_DEFAULT;
>  EXPORT_SYMBOL(sbi_spec_version);
>
> +static void __sbi_set_timer_none(uint64_t stime_value) {}
> +
> +static int __sbi_send_ipi_none(const unsigned long *hart_mask)
> +{
> +       return -EOPNOTSUPP;
> +}
> +
>  static int __sbi_rfence_none(int fid, const unsigned long *hart_mask,
>                              unsigned long start, unsigned long size,
>                              unsigned long arg4, unsigned long arg5)
> @@ -21,8 +28,9 @@ static int __sbi_rfence_none(int fid, const unsigned long *hart_mask,
>         return -EOPNOTSUPP;
>  }
>
> -static void (*__sbi_set_timer)(uint64_t stime) __ro_after_init;
> -static int (*__sbi_send_ipi)(const unsigned long *hart_mask) __ro_after_init;
> +static void (*__sbi_set_timer)(uint64_t stime) __ro_after_init = __sbi_set_timer_none;
> +static int (*__sbi_send_ipi)(const unsigned long *hart_mask)
> +                           __ro_after_init = __sbi_send_ipi_none;
>  static int (*__sbi_rfence)(int fid, const unsigned long *hart_mask,
>                            unsigned long start, unsigned long size,
>                            unsigned long arg4, unsigned long arg5)
> --
> 2.30.2
>
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

-- 
Regards,
Atish

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