linux-kernel - Re: [PATCHv8 02/17] x86/asm: Introduce inline memcpy and memset

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Message-ID: <49f7c370-1e28-494b-96a9-f45e06ed4631@intel.com>
Date: Thu, 3 Jul 2025 10:13:44 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
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Subject: Re: [PATCHv8 02/17] x86/asm: Introduce inline memcpy and memset

On 7/1/25 02:58, Kirill A. Shutemov wrote:
> Extract memcpy and memset functions from copy_user_generic() and
> __clear_user().
> 
> They can be used as inline memcpy and memset instead of the GCC builtins
> whenever necessary. LASS requires them to handle text_poke.

Why are we messing with the normal user copy functions? Code reuse is
great, but as you're discovering, the user copy code is highly
specialized and not that easy to reuse for other things.

Don't we just need a dirt simple chunk of code that does (logically):

	stac();
	asm("rep stosq...");
	clac();

Performance doesn't matter for text poking, right? It could be stosq or
anything else that you can inline. It could be a for() loop for all I
care as long as the compiler doesn't transform it into some out-of-line
memset. Right?