linux-kernel - Re: [PATCH v1 2/3] x86/msr: Switch between WRMSRNS and WRMSR with the alternatives mechanism

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Message-ID: <871q302ofz.ffs@tglx>
Date: Wed, 07 Aug 2024 20:11:12 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: "Xin Li (Intel)" <xin@...or.com>, linux-kernel@...r.kernel.org
Cc: mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
 x86@...nel.org, hpa@...or.com, peterz@...radead.org,
 andrew.cooper3@...rix.com, seanjc@...gle.com
Subject: Re: [PATCH v1 2/3] x86/msr: Switch between WRMSRNS and WRMSR with
 the alternatives mechanism

On Tue, Aug 06 2024 at 22:47, Xin Li wrote:
>  
> +/* Instruction opcode for WRMSRNS supported in binutils >= 2.40 */
> +#define WRMSRNS _ASM_BYTES(0x0f,0x01,0xc6)
> +
> +/* Non-serializing WRMSR, when available.  Falls back to a serializing WRMSR. */
>  static __always_inline void wrmsrns(u32 msr, u64 val)
>  {
> -	__wrmsrns(msr, val, val >> 32);
> +	/*
> +	 * WRMSR is 2 bytes.  WRMSRNS is 3 bytes.  Pad WRMSR with a redundant
> +	 * DS prefix to avoid a trailing NOP.
> +	 */
> +	asm volatile("1: "
> +		     ALTERNATIVE("ds wrmsr",
> +				 WRMSRNS, X86_FEATURE_WRMSRNS)

Please get rid of this horrible line break. You have 100 characters line width.

Thanks,

        tglx