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 X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A164BC388F7 for ; Sat, 31 Oct 2020 11:42:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 66BB0206D5 for ; Sat, 31 Oct 2020 11:42:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604144542; bh=nw28/nv4RREXmCNiONjPEjIKWC5A66d799+PkDq2d94=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=XVc1Q31F9tswkieevD7bSX+yzvswmjMACsei5JOOy0Zd35/GEEwO6Ad1k1snyqyDM N5d2pBbSk/jyK9QK8rHjYpKswqT6YfuRfJUYCUeWLp4oGuEfGyzI1nCYxkOb6t6TZk bf0HnJZovCXQjIguKRL5P03zBjthrJkkxHPfBwbM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727842AbgJaLmV (ORCPT ); Sat, 31 Oct 2020 07:42:21 -0400 Received: from mail.kernel.org ([198.145.29.99]:41786 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727086AbgJaLmQ (ORCPT ); Sat, 31 Oct 2020 07:42:16 -0400 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 53D69205F4; Sat, 31 Oct 2020 11:42:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604144535; bh=nw28/nv4RREXmCNiONjPEjIKWC5A66d799+PkDq2d94=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nr2uS8D3tkNGJUgYu3hG3c0Lzm9D95x4oSnBQyJJ0DfJLgqy33NuD2b1vmBMzBO24 EDpicA2XT8w8g7xByq0HWsH7xSbqZs2S5++Pw31rWCMmLRTm/BVhXUcDafMERSYO6y 7CDbr8b6CqKmprJciIqYhsMZdNSeKpdfx9cu+zBg= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Erwin Tsaur , 0day robot , Dan Williams , Borislav Petkov , Tony Luck Subject: [PATCH 5.8 25/70] x86/copy_mc: Introduce copy_mc_enhanced_fast_string() Date: Sat, 31 Oct 2020 12:35:57 +0100 Message-Id: <20201031113500.710656518@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201031113459.481803250@linuxfoundation.org> References: <20201031113459.481803250@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dan Williams commit 5da8e4a658109e3b7e1f45ae672b7c06ac3e7158 upstream. The motivations to go rework memcpy_mcsafe() are that the benefit of doing slow and careful copies is obviated on newer CPUs, and that the current opt-in list of CPUs to instrument recovery is broken relative to those CPUs. There is no need to keep an opt-in list up to date on an ongoing basis if pmem/dax operations are instrumented for recovery by default. With recovery enabled by default the old "mcsafe_key" opt-in to careful copying can be made a "fragile" opt-out. Where the "fragile" list takes steps to not consume poison across cachelines. The discussion with Linus made clear that the current "_mcsafe" suffix was imprecise to a fault. The operations that are needed by pmem/dax are to copy from a source address that might throw #MC to a destination that may write-fault, if it is a user page. So copy_to_user_mcsafe() becomes copy_mc_to_user() to indicate the separate precautions taken on source and destination. copy_mc_to_kernel() is introduced as a non-SMAP version that does not expect write-faults on the destination, but is still prepared to abort with an error code upon taking #MC. The original copy_mc_fragile() implementation had negative performance implications since it did not use the fast-string instruction sequence to perform copies. For this reason copy_mc_to_kernel() fell back to plain memcpy() to preserve performance on platforms that did not indicate the capability to recover from machine check exceptions. However, that capability detection was not architectural and now that some platforms can recover from fast-string consumption of memory errors the memcpy() fallback now causes these more capable platforms to fail. Introduce copy_mc_enhanced_fast_string() as the fast default implementation of copy_mc_to_kernel() and finalize the transition of copy_mc_fragile() to be a platform quirk to indicate 'copy-carefully'. With this in place, copy_mc_to_kernel() is fast and recovery-ready by default regardless of hardware capability. Thanks to Vivek for identifying that copy_user_generic() is not suitable as the copy_mc_to_user() backend since the #MC handler explicitly checks ex_has_fault_handler(). Thanks to the 0day robot for catching a performance bug in the x86/copy_mc_to_user implementation. [ bp: Add the "why" for this change from the 0/2th message, massage. ] Fixes: 92b0729c34ca ("x86/mm, x86/mce: Add memcpy_mcsafe()") Reported-by: Erwin Tsaur Reported-by: 0day robot Signed-off-by: Dan Williams Signed-off-by: Borislav Petkov Reviewed-by: Tony Luck Tested-by: Erwin Tsaur Cc: Link: https://lkml.kernel.org/r/160195562556.2163339.18063423034951948973.stgit@dwillia2-desk3.amr.corp.intel.com Signed-off-by: Greg Kroah-Hartman --- arch/x86/lib/copy_mc.c | 32 +++++++++++++++++++++++--------- arch/x86/lib/copy_mc_64.S | 36 ++++++++++++++++++++++++++++++++++++ tools/objtool/check.c | 1 + 3 files changed, 60 insertions(+), 9 deletions(-) --- a/arch/x86/lib/copy_mc.c +++ b/arch/x86/lib/copy_mc.c @@ -45,6 +45,8 @@ void enable_copy_mc_fragile(void) #define copy_mc_fragile_enabled (0) #endif +unsigned long copy_mc_enhanced_fast_string(void *dst, const void *src, unsigned len); + /** * copy_mc_to_kernel - memory copy that handles source exceptions * @@ -52,9 +54,11 @@ void enable_copy_mc_fragile(void) * @src: source address * @len: number of bytes to copy * - * Call into the 'fragile' version on systems that have trouble - * actually do machine check recovery. Everyone else can just - * use memcpy(). + * Call into the 'fragile' version on systems that benefit from avoiding + * corner case poison consumption scenarios, For example, accessing + * poison across 2 cachelines with a single instruction. Almost all + * other uses case can use copy_mc_enhanced_fast_string() for a fast + * recoverable copy, or fallback to plain memcpy. * * Return 0 for success, or number of bytes not copied if there was an * exception. @@ -63,6 +67,8 @@ unsigned long __must_check copy_mc_to_ke { if (copy_mc_fragile_enabled) return copy_mc_fragile(dst, src, len); + if (static_cpu_has(X86_FEATURE_ERMS)) + return copy_mc_enhanced_fast_string(dst, src, len); memcpy(dst, src, len); return 0; } @@ -72,11 +78,19 @@ unsigned long __must_check copy_mc_to_us { unsigned long ret; - if (!copy_mc_fragile_enabled) - return copy_user_generic(dst, src, len); + if (copy_mc_fragile_enabled) { + __uaccess_begin(); + ret = copy_mc_fragile(dst, src, len); + __uaccess_end(); + return ret; + } + + if (static_cpu_has(X86_FEATURE_ERMS)) { + __uaccess_begin(); + ret = copy_mc_enhanced_fast_string(dst, src, len); + __uaccess_end(); + return ret; + } - __uaccess_begin(); - ret = copy_mc_fragile(dst, src, len); - __uaccess_end(); - return ret; + return copy_user_generic(dst, src, len); } --- a/arch/x86/lib/copy_mc_64.S +++ b/arch/x86/lib/copy_mc_64.S @@ -124,4 +124,40 @@ EXPORT_SYMBOL_GPL(copy_mc_fragile) _ASM_EXTABLE(.L_write_words, .E_write_words) _ASM_EXTABLE(.L_write_trailing_bytes, .E_trailing_bytes) #endif /* CONFIG_X86_MCE */ + +/* + * copy_mc_enhanced_fast_string - memory copy with exception handling + * + * Fast string copy + fault / exception handling. If the CPU does + * support machine check exception recovery, but does not support + * recovering from fast-string exceptions then this CPU needs to be + * added to the copy_mc_fragile_key set of quirks. Otherwise, absent any + * machine check recovery support this version should be no slower than + * standard memcpy. + */ +SYM_FUNC_START(copy_mc_enhanced_fast_string) + movq %rdi, %rax + movq %rdx, %rcx +.L_copy: + rep movsb + /* Copy successful. Return zero */ + xorl %eax, %eax + ret +SYM_FUNC_END(copy_mc_enhanced_fast_string) + + .section .fixup, "ax" +.E_copy: + /* + * On fault %rcx is updated such that the copy instruction could + * optionally be restarted at the fault position, i.e. it + * contains 'bytes remaining'. A non-zero return indicates error + * to copy_mc_generic() users, or indicate short transfers to + * user-copy routines. + */ + movq %rcx, %rax + ret + + .previous + + _ASM_EXTABLE_FAULT(.L_copy, .E_copy) #endif /* !CONFIG_UML */ --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -550,6 +550,7 @@ static const char *uaccess_safe_builtin[ "csum_partial_copy_generic", "copy_mc_fragile", "copy_mc_fragile_handle_tail", + "copy_mc_enhanced_fast_string", "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */ NULL };