linux-kernel - Re: [PATCH] riscv: require alternatives framework when selecting FPU support

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Message-ID: <20230322124631.7p67thzeblrawsqj@orel>
Date:   Wed, 22 Mar 2023 13:46:31 +0100
From:   Andrew Jones <ajones@...tanamicro.com>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Jisheng Zhang <jszhang@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup@...infault.org>,
        Atish Patra <atishp@...shpatra.org>,
        Heiko Stuebner <heiko@...ech.de>,
        Conor Dooley <conor.dooley@...rochip.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org,
        regressions@...mhuis.info, regressions@...ts.linux.dev
Subject: Re: [PATCH] riscv: require alternatives framework when selecting FPU
 support

On Wed, Mar 22, 2023 at 01:09:07PM +0100, Jason A. Donenfeld wrote:
> When moving switch_to's has_fpu() over to using riscv_has_extension_
> likely() rather than static branchs, the FPU code gained a dependency on
> the alternatives framework. If CONFIG_RISCV_ALTERNATIVE isn't selected
> when CONFIG_FPU is, then has_fpu() returns false, and switch_to does not
> work as intended. So select CONFIG_RISCV_ALTERNATIVE when CONFIG_FPU is
> selected.
> 
> Fixes: 702e64550b12 ("riscv: fpu: switch has_fpu() to riscv_has_extension_likely()")
> Link: https://lore.kernel.org/all/ZBruFRwt3rUVngPu@zx2c4.com/
> Cc: Jisheng Zhang <jszhang@...nel.org>
> Cc: Andrew Jones <ajones@...tanamicro.com>
> Cc: Heiko Stuebner <heiko@...ech.de>
> Cc: Conor Dooley <conor.dooley@...rochip.com>
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
>  arch/riscv/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index c5e42cc37604..0f59350c699d 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -467,6 +467,7 @@ config TOOLCHAIN_HAS_ZIHINTPAUSE
>  config FPU
>  	bool "FPU support"
>  	default y
> +	select RISCV_ALTERNATIVE
>  	help
>  	  Say N here if you want to disable all floating-point related procedure
>  	  in the kernel.
> -- 
> 2.40.0
>

Reviewed-by: Andrew Jones <ajones@...tanamicro.com>

I took a look to see if we missed anything else and see that we should
do the same patch for KVM. I'll send one.

(It's tempting to just select RISCV_ALTERNATIVE from RISCV, but maybe we
 can defer that wedding a bit longer.)

Thanks,
drew