linux-kernel - Re: [PATCH v4 1/5] x86/asm: move the raw asm in iosubmit_cmds512() to special

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Date:   Wed, 23 Sep 2020 12:41:58 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Dave Jiang <dave.jiang@...el.com>
Cc:     vkoul@...nel.org, tglx@...utronix.de, mingo@...hat.com,
        dan.j.williams@...el.com, tony.luck@...el.com, jing.lin@...el.com,
        ashok.raj@...el.com, sanjay.k.kumar@...el.com,
        fenghua.yu@...el.com, kevin.tian@...el.com,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/5] x86/asm: move the raw asm in iosubmit_cmds512()
 to special_insns.h

> Subject: Re: [PATCH v4 1/5] x86/asm: move the raw asm in iosubmit_cmds512() to special_insns.h

Start patch name with a capital letter: "Move the asm definition.."

Also, calling stuff "raw" and "core" is misleading in the kernel context
- you wanna say simply: "Carve out a generic movdir64b() helper... "

On Thu, Sep 17, 2020 at 02:15:16PM -0700, Dave Jiang wrote:
> diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h
> index 59a3e13204c3..7bc8e714f37e 100644
> --- a/arch/x86/include/asm/special_insns.h
> +++ b/arch/x86/include/asm/special_insns.h
> @@ -234,6 +234,23 @@ static inline void clwb(volatile void *__p)
>  
>  #define nop() asm volatile ("nop")
>  
> +static inline void movdir64b(void *__dst, const void *src)

Make __dst be the function local variable name and keep "dst", i.e.,
without the underscores, the function parameter name.

> +	/*
> +	 * Note that this isn't an "on-stack copy", just definition of "dst"
> +	 * as a pointer to 64-bytes of stuff that is going to be overwritten.
> +	 * In the MOVDIR64B case that may be needed as you can use the
> +	 * MOVDIR64B instruction to copy arbitrary memory around. This trick
> +	 * lets the compiler know how much gets clobbered.
> +	 */
> +	volatile struct { char _[64]; } *dst = __dst;
> +
> +	/* MOVDIR64B [rdx], rax */
> +	asm volatile(".byte 0x66, 0x0f, 0x38, 0xf8, 0x02"
> +		     : "=m" (dst)
> +		     : "d" (src), "a" (dst));
> +}
> +
>  #endif /* __KERNEL__ */
>  
>  #endif /* _ASM_X86_SPECIAL_INSNS_H */
> 

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette