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Message-ID: <otaa7t5kq4wtj5zk3vis7ldqw56i7bwzga7yg7pskgeps7zthg@fthlgikkmlhh>
Date: Fri, 4 Jul 2025 12:04:25 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Andy Lutomirski <luto@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, 
	Peter Zijlstra <peterz@...radead.org>, Ard Biesheuvel <ardb@...nel.org>, 
	"Paul E. McKenney" <paulmck@...nel.org>, Josh Poimboeuf <jpoimboe@...nel.org>, 
	Xiongwei Song <xiongwei.song@...driver.com>, Xin Li <xin3.li@...el.com>, 
	"Mike Rapoport (IBM)" <rppt@...nel.org>, Brijesh Singh <brijesh.singh@....com>, 
	Michael Roth <michael.roth@....com>, Tony Luck <tony.luck@...el.com>, 
	Alexey Kardashevskiy <aik@....com>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
	Jonathan Corbet <corbet@....net>, Sohil Mehta <sohil.mehta@...el.com>, 
	Ingo Molnar <mingo@...nel.org>, Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, 
	Daniel Sneddon <daniel.sneddon@...ux.intel.com>, Kai Huang <kai.huang@...el.com>, 
	Sandipan Das <sandipan.das@....com>, Breno Leitao <leitao@...ian.org>, 
	Rick Edgecombe <rick.p.edgecombe@...el.com>, Alexei Starovoitov <ast@...nel.org>, 
	Hou Tao <houtao1@...wei.com>, Juergen Gross <jgross@...e.com>, 
	Vegard Nossum <vegard.nossum@...cle.com>, Kees Cook <kees@...nel.org>, Eric Biggers <ebiggers@...gle.com>, 
	Jason Gunthorpe <jgg@...pe.ca>, "Masami Hiramatsu (Google)" <mhiramat@...nel.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Luis Chamberlain <mcgrof@...nel.org>, 
	Yuntao Wang <ytcoode@...il.com>, Rasmus Villemoes <linux@...musvillemoes.dk>, 
	Christophe Leroy <christophe.leroy@...roup.eu>, Tejun Heo <tj@...nel.org>, Changbin Du <changbin.du@...wei.com>, 
	Huang Shijie <shijie@...amperecomputing.com>, Geert Uytterhoeven <geert+renesas@...der.be>, 
	Namhyung Kim <namhyung@...nel.org>, Arnaldo Carvalho de Melo <acme@...hat.com>, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org, 
	linux-mm@...ck.org
Subject: Re: [PATCHv8 02/17] x86/asm: Introduce inline memcpy and memset

On Thu, Jul 03, 2025 at 10:13:44AM -0700, Dave Hansen wrote:
> 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?

Yeah, performance doesn't matter for text poking. And this approach
simplifies the code quite a bit. I will use direct asm() for text poke.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

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