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, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 8B234C4727F for ; Wed, 23 Sep 2020 17:00:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 508AC206BE for ; Wed, 23 Sep 2020 17:00:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726744AbgIWRAd (ORCPT ); Wed, 23 Sep 2020 13:00:33 -0400 Received: from mga01.intel.com ([192.55.52.88]:53062 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726342AbgIWRAd (ORCPT ); Wed, 23 Sep 2020 13:00:33 -0400 IronPort-SDR: gdsSle//WznQkkUjb3H+CmyOd7kIIkBhUDYZ+8Xs+J+zvpQGnhbPAkGUQs6Njd2H/kHZvE0jpJ lBb7txvvVsiw== X-IronPort-AV: E=McAfee;i="6000,8403,9753"; a="179039892" X-IronPort-AV: E=Sophos;i="5.77,293,1596524400"; d="scan'208";a="179039892" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Sep 2020 10:00:32 -0700 IronPort-SDR: jnHAKwgf8h4PajpgTsZPB6zIhrdKJGUsVrBsIVLBdmuexYjdqgi5B04gncq89JRYdUDRJRG3Vk 1CuXEALuFCUg== X-IronPort-AV: E=Sophos;i="5.77,293,1596524400"; d="scan'208";a="342495812" Received: from dwillia2-desk3.jf.intel.com (HELO dwillia2-desk3.amr.corp.intel.com) ([10.54.39.16]) by fmsmga002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Sep 2020 10:00:32 -0700 Subject: [PATCH v9 2/2] x86/copy_mc: Introduce copy_mc_generic() From: Dan Williams To: mingo@redhat.com Cc: x86@kernel.org, stable@vger.kernel.org, Borislav Petkov , Vivek Goyal , "H. Peter Anvin" , Andy Lutomirski , Thomas Gleixner , Peter Zijlstra , Linus Torvalds , Tony Luck , Erwin Tsaur , Erwin Tsaur , 0day robot , tglx@linutronix.de, x86@kernel.org, linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org, jack@suse.cz Date: Wed, 23 Sep 2020 09:42:09 -0700 Message-ID: <160087932379.3520.599786267031023589.stgit@dwillia2-desk3.amr.corp.intel.com> In-Reply-To: <160087928642.3520.17063139768910633998.stgit@dwillia2-desk3.amr.corp.intel.com> References: <160087928642.3520.17063139768910633998.stgit@dwillia2-desk3.amr.corp.intel.com> User-Agent: StGit/0.18-3-g996c MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 platform 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_generic() 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 'fragility'. 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. Cc: x86@kernel.org Cc: Cc: Ingo Molnar Cc: Borislav Petkov Cc: Vivek Goyal Cc: "H. Peter Anvin" Cc: Andy Lutomirski Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Linus Torvalds Reviewed-by: Tony Luck Reported-by: Erwin Tsaur Tested-by: Erwin Tsaur Reported-by: 0day robot Fixes: 92b0729c34ca ("x86/mm, x86/mce: Add memcpy_mcsafe()") Signed-off-by: Dan Williams --- arch/x86/include/asm/uaccess.h | 3 +++ arch/x86/lib/copy_mc.c | 13 ++++++------- arch/x86/lib/copy_mc_64.S | 40 ++++++++++++++++++++++++++++++++++++++++ tools/objtool/check.c | 1 + 4 files changed, 50 insertions(+), 7 deletions(-) diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index 9bed6471c7f3..4935833cc891 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -467,6 +467,9 @@ copy_mc_to_user(void *to, const void *from, unsigned len); unsigned long __must_check copy_mc_fragile(void *dst, const void *src, unsigned cnt); + +unsigned long __must_check +copy_mc_generic(void *dst, const void *src, unsigned cnt); #else static inline void enable_copy_mc_fragile(void) { diff --git a/arch/x86/lib/copy_mc.c b/arch/x86/lib/copy_mc.c index cdb8f5dc403d..afac844c8f45 100644 --- a/arch/x86/lib/copy_mc.c +++ b/arch/x86/lib/copy_mc.c @@ -23,7 +23,7 @@ void enable_copy_mc_fragile(void) * * Call into the 'fragile' version on systems that have trouble * actually do machine check recovery. Everyone else can just - * use memcpy(). + * use copy_mc_generic(). * * Return 0 for success, or number of bytes not copied if there was an * exception. @@ -33,8 +33,7 @@ copy_mc_to_kernel(void *dst, const void *src, unsigned cnt) { if (static_branch_unlikely(©_mc_fragile_key)) return copy_mc_fragile(dst, src, cnt); - memcpy(dst, src, cnt); - return 0; + return copy_mc_generic(dst, src, cnt); } EXPORT_SYMBOL_GPL(copy_mc_to_kernel); @@ -56,11 +55,11 @@ copy_mc_to_user(void *to, const void *from, unsigned len) { unsigned long ret; - if (!static_branch_unlikely(©_mc_fragile_key)) - return copy_user_generic(to, from, len); - __uaccess_begin(); - ret = copy_mc_fragile(to, from, len); + if (static_branch_unlikely(©_mc_fragile_key)) + ret = copy_mc_fragile(to, from, len); + else + ret = copy_mc_generic(to, from, len); __uaccess_end(); return ret; } diff --git a/arch/x86/lib/copy_mc_64.S b/arch/x86/lib/copy_mc_64.S index 35a67c50890b..a08e7a4d9e28 100644 --- a/arch/x86/lib/copy_mc_64.S +++ b/arch/x86/lib/copy_mc_64.S @@ -2,7 +2,9 @@ /* Copyright(c) 2016-2020 Intel Corporation. All rights reserved. */ #include +#include #include +#include #include #include @@ -122,4 +124,42 @@ EXPORT_SYMBOL_GPL(copy_mc_fragile) _ASM_EXTABLE(.L_write_leading_bytes, .E_leading_bytes) _ASM_EXTABLE(.L_write_words, .E_write_words) _ASM_EXTABLE(.L_write_trailing_bytes, .E_trailing_bytes) + +/* + * copy_mc_generic - 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_generic) + ALTERNATIVE "jmp copy_mc_fragile", "", X86_FEATURE_ERMS + movq %rdi, %rax + movq %rdx, %rcx +.L_copy: + rep movsb + /* Copy successful. Return zero */ + xorl %eax, %eax + ret +SYM_FUNC_END(copy_mc_generic) +EXPORT_SYMBOL_GPL(copy_mc_generic) + + .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 diff --git a/tools/objtool/check.c b/tools/objtool/check.c index cf2d076f6ba5..9677dfa0f983 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -548,6 +548,7 @@ static const char *uaccess_safe_builtin[] = { "__ubsan_handle_shift_out_of_bounds", /* misc */ "csum_partial_copy_generic", + "copy_mc_generic", "copy_mc_fragile", "copy_mc_fragile_handle_tail", "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */