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Date:   Wed, 22 Mar 2023 13:46:31 +0100
From:   Andrew Jones <ajones@ventanamicro.com>
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     Jisheng Zhang <jszhang@kernel.org>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Anup Patel <anup@brainfault.org>,
        Atish Patra <atishp@atishpatra.org>,
        Heiko Stuebner <heiko@sntech.de>,
        Conor Dooley <conor.dooley@microchip.com>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, kvm-riscv@lists.infradead.org,
        regressions@leemhuis.info, regressions@lists.linux.dev
Subject: Re: [PATCH] riscv: require alternatives framework when selecting FPU
 support
Message-ID: <20230322124631.7p67thzeblrawsqj@orel>
References: <ZBruFRwt3rUVngPu@zx2c4.com>
 <20230322120907.2968494-1-Jason@zx2c4.com>
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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@kernel.org>
> Cc: Andrew Jones <ajones@ventanamicro.com>
> Cc: Heiko Stuebner <heiko@sntech.de>
> Cc: Conor Dooley <conor.dooley@microchip.com>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.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@ventanamicro.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