From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 17C2FC3DA78 for ; Sat, 14 Jan 2023 16:17:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229682AbjANQRk (ORCPT ); Sat, 14 Jan 2023 11:17:40 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54340 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229609AbjANQRg (ORCPT ); Sat, 14 Jan 2023 11:17:36 -0500 Received: from mail.skyhub.de (mail.skyhub.de [5.9.137.197]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8CEEC83DD for ; Sat, 14 Jan 2023 08:17:35 -0800 (PST) Received: from zn.tnic (p5de8e9fe.dip0.t-ipconnect.de [93.232.233.254]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 2DCC61EC050B; Sat, 14 Jan 2023 17:17:34 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1673713054; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=tCppwdAyk0xCDR6yNSq4nEzTRHs/1KkFCfDo0KrtlWk=; b=LesZi11kzjR5X1Ruh9qvR1UHcYHvlUeAHNI6IsqqrhnGzrbfrBhykuqAY0JNjLSfijjCdG sd1MUmHlv4dhzIbYdgrXuZXX5vZ/0ZLciFQ3Z1E8U3Yj2xeAGkToFEFCV9uDHSuFbjTJR7 cb2WpBUOe7TpnbRMG5tspHtz0yGZa1I= Date: Sat, 14 Jan 2023 17:17:28 +0100 From: Borislav Petkov To: Daniel Verkamp Cc: x86@kernel.org, Tony Luck , Jiri Slaby , lkml Subject: Re: [PATCH] x86: combine memmove FSRM and ERMS alternatives Message-ID: References: <20230113203427.1111689-1-dverkamp@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 14, 2023 at 11:42:13AM +0100, Borislav Petkov wrote: > Or, altenatively (pun intended), you can do what copy_user_generic() does and > move all that logic into C and inline asm. Which I'd prefer, actually, instead of > doing ugly asm hacks. Depends on how ugly it gets... Alternatively #2, you can do the below as a minimal fix for stable along with explaining what we're doing there and why and then do the other things I suggested - if you'd like, that is - later and with no pressure. Thx. --- diff --git a/arch/x86/lib/memmove_64.S b/arch/x86/lib/memmove_64.S index 02661861e5dd..d6ffb4164cdb 100644 --- a/arch/x86/lib/memmove_64.S +++ b/arch/x86/lib/memmove_64.S @@ -38,10 +38,9 @@ SYM_FUNC_START(__memmove) cmp %rdi, %r8 jg 2f - /* FSRM implies ERMS => no length checks, do the copy directly */ .Lmemmove_begin_forward: ALTERNATIVE "cmp $0x20, %rdx; jb 1f", "", X86_FEATURE_FSRM - ALTERNATIVE "", "jmp .Lmemmove_erms", X86_FEATURE_ERMS + ALTERNATIVE "cmp $0x20, %rdx; jb 1f", "jmp .Lmemmove_erms", X86_FEATURE_ERMS /* * movsq instruction have many startup latency -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette