linux-kernel - Re: [PATCH v4 05/11] tools: riscv: Add header file vdso/processor.h

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Date:   Wed, 13 Dec 2023 15:02:51 +0100
From:   Andrew Jones <ajones@...tanamicro.com>
To:     Haibo Xu <haibo1.xu@...el.com>
Cc:     xiaobo55x@...il.com, Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Shuah Khan <shuah@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Anup Patel <anup@...infault.org>,
        Atish Patra <atishp@...shpatra.org>,
        Guo Ren <guoren@...nel.org>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Mayuresh Chitale <mchitale@...tanamicro.com>,
        Daniel Henrique Barboza <dbarboza@...tanamicro.com>,
        Jisheng Zhang <jszhang@...nel.org>,
        Samuel Holland <samuel@...lland.org>,
        Minda Chen <minda.chen@...rfivetech.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Peter Xu <peterx@...hat.com>, Like Xu <likexu@...cent.com>,
        Vipin Sharma <vipinsh@...gle.com>,
        Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>,
        Thomas Huth <thuth@...hat.com>,
        Aaron Lewis <aaronlewis@...gle.com>,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        kvm-riscv@...ts.infradead.org
Subject: Re: [PATCH v4 05/11] tools: riscv: Add header file vdso/processor.h

On Tue, Dec 12, 2023 at 05:31:14PM +0800, Haibo Xu wrote:
> Borrow the cpu_relax() definitions from kernel's
> arch/riscv/include/asm/vdso/processor.h to tools/ for riscv.
> 
> Signed-off-by: Haibo Xu <haibo1.xu@...el.com>
> ---
>  tools/arch/riscv/include/asm/vdso/processor.h | 32 +++++++++++++++++++
>  1 file changed, 32 insertions(+)
>  create mode 100644 tools/arch/riscv/include/asm/vdso/processor.h
> 
> diff --git a/tools/arch/riscv/include/asm/vdso/processor.h b/tools/arch/riscv/include/asm/vdso/processor.h
> new file mode 100644
> index 000000000000..662aca039848
> --- /dev/null
> +++ b/tools/arch/riscv/include/asm/vdso/processor.h
> @@ -0,0 +1,32 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +#ifndef __ASM_VDSO_PROCESSOR_H
> +#define __ASM_VDSO_PROCESSOR_H
> +
> +#ifndef __ASSEMBLY__
> +
> +#include <asm-generic/barrier.h>
> +
> +static inline void cpu_relax(void)
> +{
> +#ifdef __riscv_muldiv
> +	int dummy;
> +	/* In lieu of a halt instruction, induce a long-latency stall. */
> +	__asm__ __volatile__ ("div %0, %0, zero" : "=r" (dummy));
> +#endif
> +
> +#ifdef CONFIG_TOOLCHAIN_HAS_ZIHINTPAUSE
> +	/*
> +	 * Reduce instruction retirement.
> +	 * This assumes the PC changes.
> +	 */
> +	__asm__ __volatile__ ("pause");
> +#else
> +	/* Encoding of the pause instruction */
> +	__asm__ __volatile__ (".4byte 0x100000F");
> +#endif
> +	barrier();
> +}
> +
> +#endif /* __ASSEMBLY__ */
> +
> +#endif /* __ASM_VDSO_PROCESSOR_H */
> -- 
> 2.34.1
>

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