Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933635AbbLORpH (ORCPT ); Tue, 15 Dec 2015 12:45:07 -0500 Received: from mail-qk0-f176.google.com ([209.85.220.176]:34749 "EHLO mail-qk0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932211AbbLORpF (ORCPT ); Tue, 15 Dec 2015 12:45:05 -0500 MIME-Version: 1.0 In-Reply-To: <20151215131135.GE25973@pd.tnic> References: <23b2515da9d06b198044ad83ca0a15ba38c24e6e.1449861203.git.tony.luck@intel.com> <20151215131135.GE25973@pd.tnic> Date: Tue, 15 Dec 2015 09:45:04 -0800 Message-ID: Subject: Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover from machine checks From: Dan Williams To: Borislav Petkov Cc: Tony Luck , Ingo Molnar , Andrew Morton , Andy Lutomirski , "linux-kernel@vger.kernel.org" , Linux MM , linux-nvdimm , X86 ML Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2189 Lines: 46 On Tue, Dec 15, 2015 at 5:11 AM, Borislav Petkov wrote: > On Thu, Dec 10, 2015 at 04:21:50PM -0800, Tony Luck wrote: >> Using __copy_user_nocache() as inspiration create a memory copy >> routine for use by kernel code with annotations to allow for >> recovery from machine checks. >> >> Notes: >> 1) Unlike the original we make no attempt to copy all the bytes >> up to the faulting address. The original achieves that by >> re-executing the failing part as a byte-by-byte copy, >> which will take another page fault. We don't want to have >> a second machine check! >> 2) Likewise the return value for the original indicates exactly >> how many bytes were not copied. Instead we provide the physical >> address of the fault (thanks to help from do_machine_check() >> 3) Provide helpful macros to decode the return value. >> >> Signed-off-by: Tony Luck >> --- >> arch/x86/include/asm/uaccess_64.h | 5 +++ >> arch/x86/kernel/x8664_ksyms_64.c | 2 + >> arch/x86/lib/copy_user_64.S | 91 +++++++++++++++++++++++++++++++++++++++ >> 3 files changed, 98 insertions(+) > > ... > >> + * mcsafe_memcpy - Uncached memory copy with machine check exception handling >> + * Note that we only catch machine checks when reading the source addresses. >> + * Writes to target are posted and don't generate machine checks. >> + * This will force destination/source out of cache for more performance. > > ... and the non-temporal version is the optimal one even though we're > defaulting to copy_user_enhanced_fast_string for memcpy on modern Intel > CPUs...? At least the pmem driver use case does not want caching of the source-buffer since that is the raw "disk" media. I.e. in pmem_do_bvec() we'd use this to implement memcpy_from_pmem(). However, caching the destination-buffer may prove beneficial since that data is likely to be consumed immediately by the thread that submitted the i/o. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/