linux-kernel - Re: [PATCH] x86/cpufeatures: Add enumeration for serialize instruction

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Date:   Fri, 3 Apr 2020 10:12:17 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Ricardo Neri <ricardo.neri@...el.com>, x86@...nel.org,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>
Subject: Re: [PATCH] x86/cpufeatures: Add enumeration for serialize
 instruction

On Thu, Apr 02, 2020 at 06:40:26PM -0700, Ricardo Neri wrote:
> The serialize instruction ensures that before the next instruction is
> fetched and executed, all the modifications to flags, registers, and memory
> made by previous instructions are completed, draining all buffered writes
> to memory.
> 
> Importantly, the serialize instruction does not modify registers,
> arithmetic flags or memory.
> 
> Hence, the serialize instructions provides a better way for software
> to serialize execution than using instructions such as cpuid, which does
> modify registers and, in virtual machines, causes a VM exit.
> 
> This instruction is supported by the CPU if CPUID.7H.EDX[bit 14] is
> set.
> 
> Cc: x86@...nel.org
> Cc: "Ravi V. Shankar" <ravi.v.shankar@...el.com>
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> ---
> This new instruction is documented in the latest version of the Intel
> Architecture Instruction Set Extensions and Future Features Programming
> Reference Chapter 2.1 located at
> https://software.intel.com/sites/default/files/managed/c5/15/architecture-instruction-set-extensions-programming-reference.pdf
> ---
>  arch/x86/include/asm/cpufeatures.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index db189945e9b0..cd9b1ec022ec 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -364,6 +364,7 @@
>  #define X86_FEATURE_AVX512_VP2INTERSECT (18*32+ 8) /* AVX-512 Intersect for D/Q */
>  #define X86_FEATURE_MD_CLEAR		(18*32+10) /* VERW clears CPU buffers */
>  #define X86_FEATURE_TSX_FORCE_ABORT	(18*32+13) /* "" TSX_FORCE_ABORT */
> +#define X86_FEATURE_SERIALIZE		(18*32+14) /* SERIALIZE instruction */
>  #define X86_FEATURE_PCONFIG		(18*32+18) /* Intel PCONFIG */
>  #define X86_FEATURE_SPEC_CTRL		(18*32+26) /* "" Speculation Control (IBRS + IBPB) */
>  #define X86_FEATURE_INTEL_STIBP		(18*32+27) /* "" Single Thread Indirect Branch Predictors */
> -- 

Send this together with code which is using it, pls.

Thx.

-- 
Regards/Gruss,
    Boris.

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