linux-kernel - Re: [PATCH v2 01/19] riscv: hwprobe: factorize hwprobe ISA extension reporting

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Message-ID: <CALs-HssL=wNwj9nRuZwpZhy1CB9p9-X=OqgwBw9zvgA7hA4fEg@mail.gmail.com>
Date:   Wed, 18 Oct 2023 10:24:15 -0700
From:   Evan Green <evan@...osinc.com>
To:     Clément Léger <cleger@...osinc.com>
Cc:     linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        Palmer Dabbelt <palmer@...osinc.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Jonathan Corbet <corbet@....net>,
        Andrew Jones <ajones@...tanamicro.com>,
        Conor Dooley <conor@...nel.org>,
        Samuel Ortiz <sameo@...osinc.com>
Subject: Re: [PATCH v2 01/19] riscv: hwprobe: factorize hwprobe ISA extension reporting

On Tue, Oct 17, 2023 at 6:15 AM Clément Léger <cleger@...osinc.com> wrote:
>
> Factorize ISA extension reporting by using a macro rather than
> copy/pasting extension names. This will allow adding new extensions more
> easily.
>
> Signed-off-by: Clément Léger <cleger@...osinc.com>
> ---
>  arch/riscv/kernel/sys_riscv.c | 32 ++++++++++++++++++--------------
>  1 file changed, 18 insertions(+), 14 deletions(-)
>
> diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
> index 473159b5f303..e207874e686e 100644
> --- a/arch/riscv/kernel/sys_riscv.c
> +++ b/arch/riscv/kernel/sys_riscv.c
> @@ -145,20 +145,24 @@ static void hwprobe_isa_ext0(struct riscv_hwprobe *pair,
>         for_each_cpu(cpu, cpus) {
>                 struct riscv_isainfo *isainfo = &hart_isa[cpu];
>
> -               if (riscv_isa_extension_available(isainfo->isa, ZBA))
> -                       pair->value |= RISCV_HWPROBE_EXT_ZBA;
> -               else
> -                       missing |= RISCV_HWPROBE_EXT_ZBA;
> -
> -               if (riscv_isa_extension_available(isainfo->isa, ZBB))
> -                       pair->value |= RISCV_HWPROBE_EXT_ZBB;
> -               else
> -                       missing |= RISCV_HWPROBE_EXT_ZBB;
> -
> -               if (riscv_isa_extension_available(isainfo->isa, ZBS))
> -                       pair->value |= RISCV_HWPROBE_EXT_ZBS;
> -               else
> -                       missing |= RISCV_HWPROBE_EXT_ZBS;
> +#define CHECK_ISA_EXT(__ext)                                                   \
> +               do {                                                            \
> +                       if (riscv_isa_extension_available(isainfo->isa, __ext)) \
> +                               pair->value |= RISCV_HWPROBE_EXT_##__ext;       \
> +                       else                                                    \
> +                               missing |= RISCV_HWPROBE_EXT_##__ext;           \
> +               } while (false)
> +
> +               /*
> +                * Only use CHECK_ISA_EXT() for extensions which can be exposed
> +                * to userspace, regardless of the kernel's configuration, as no
> +                * other checks, besides presence in the hart_isa bitmap, are
> +                * made.

This comment alludes to a dangerous trap, but I'm having trouble
understanding what it is. Perhaps some rewording to more explicitly
state the danger would be appropriate. Other than that:

Reviewed-by: Evan Green <evan@...osinc.com>