linux-kernel - Re: [PATCH v2] RISC-V: recognize S/U mode bits in print

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Date:   Fri, 16 Nov 2018 08:52:16 -0800 (PST)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     me@...ki.ch
CC:     linux-riscv@...ts.infradead.org, me@...ki.ch,
        aou@...s.berkeley.edu, atish.patra@....com, anup@...infault.org,
        linux-kernel@...r.kernel.org
Subject:     Re: [PATCH v2] RISC-V: recognize S/U mode bits in print_isa

On Fri, 09 Nov 2018 13:42:16 PST (-0800), me@...ki.ch wrote:
> Removes the warning about an unsupported ISA when reading /proc/cpuinfo
> on QEMU. The "S" extension is not being returned as it is not accessible
> from userspace.
>
> Signed-off-by: Patrick Stählin <me@...ki.ch>
> ---
>  arch/riscv/kernel/cpu.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> index 3a5a2ee31547..b4a7d4427fbb 100644
> --- a/arch/riscv/kernel/cpu.c
> +++ b/arch/riscv/kernel/cpu.c
> @@ -64,7 +64,7 @@ int riscv_of_processor_hartid(struct device_node *node)
>
>  static void print_isa(struct seq_file *f, const char *orig_isa)
>  {
> -	static const char *ext = "mafdc";
> +	static const char *ext = "mafdcsu";
>  	const char *isa = orig_isa;
>  	const char *e;
>
> @@ -88,11 +88,14 @@ static void print_isa(struct seq_file *f, const char *orig_isa)
>  	/*
>  	 * Check the rest of the ISA string for valid extensions, printing those
>  	 * we find.  RISC-V ISA strings define an order, so we only print the
> -	 * extension bits when they're in order.
> +	 * extension bits when they're in order. Hide the supervisor (S)
> +	 * extension from userspace as it's not accessible from there.
>  	 */
>  	for (e = ext; *e != '\0'; ++e) {
>  		if (isa[0] == e[0]) {
> -			seq_write(f, isa, 1);
> +			if (isa[0] != 's')
> +				seq_write(f, isa, 1);
> +
>  			isa++;
>  		}
>  	}

This looks good to me.  I'll target it for the RCs, as it's fairly small and 
that warning fires too often.

Thanks!