From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yk0-f171.google.com (mail-yk0-f171.google.com [209.85.160.171]) by kanga.kvack.org (Postfix) with ESMTP id 58F686B0009 for ; Mon, 1 Feb 2016 18:16:55 -0500 (EST) Received: by mail-yk0-f171.google.com with SMTP id u9so35979829ykd.1 for ; Mon, 01 Feb 2016 15:16:55 -0800 (PST) Received: from mail-yk0-x231.google.com (mail-yk0-x231.google.com. [2607:f8b0:4002:c07::231]) by mx.google.com with ESMTPS id i8si12525855ybi.113.2016.02.01.15.16.54 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 01 Feb 2016 15:16:54 -0800 (PST) Received: by mail-yk0-x231.google.com with SMTP id z7so91398334yka.3 for ; Mon, 01 Feb 2016 15:16:54 -0800 (PST) MIME-Version: 1.0 In-Reply-To: References: <20160110112635.GC22896@pd.tnic> <20160111104425.GA29448@gmail.com> <20160114043956.GA8496@pd.tnic> <20160130102803.GB15296@pd.tnic> Date: Mon, 1 Feb 2016 15:16:54 -0800 Message-ID: Subject: Re: [PATCH v8 3/3] x86, mce: Add __mcsafe_copy() From: Dan Williams Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Tony Luck Cc: Ingo Molnar , Borislav Petkov , Andy Lutomirski , linux-nvdimm , "linux-kernel@vger.kernel.org" , Andrew Morton , Robert , "linux-mm@kvack.org" , X86 ML On Mon, Feb 1, 2016 at 3:10 PM, Tony Luck wrote: >> The most optimal way of alternatively calling two functions would be >> something like this, IMO: >> >> alternative_call(memcpy, __mcsafe_copy, X86_FEATURE_MCRECOVERY, >> ASM_OUTPUT2("=a" (mcsafe_ret.trapnr), "=d" (mcsafe_ret.remain)), >> "D" (dst), "S" (src), "d" (len)); >> >> I hope I've not messed up the calling convention but you want the inputs >> in %rdi, %rsi, %rdx and the outputs in %rax, %rdx, respectively. Just >> check the asm gcc generates and do not trust me :) >> >> The other thing you probably would need to do is create our own >> __memcpy() which returns struct mcsafe_ret so that the signatures of >> both functions match. >> >> Yeah, it is a bit of jumping through hoops but this way we do a CALL >> directly in asm, without any JMPs or NOPs padding the other >> alternatives methods add. >> >> But if you don't care about a small JMP and that is not a hot path, you >> could do the simpler: >> >> if (static_cpu_has(X86_FEATURE_MCRECOVERY)) >> return __mcsafe_copy(...); >> >> return memcpy(); >> >> which adds a JMP or a 5-byte NOP depending on the X86_FEATURE_MCRECOVERY >> setting. > > Dan, > > What do you want the API to look like at the point you make a call > in the libnvdimm code? Something like: > > r = nvcopy(dst, src, len); > > where the innards of nvcopy() does the check for X86_FEATURE_MCE_RECOVERY? > > What is useful to you in the return value? The low level __mcsafe_copy() returns > both a remainder and a trap number. But in your case I don't think you > need the trap > number (if the remaining count is not zero, then there must have been a #MC. #PF > isn't an option for you, right? RIght, we don't need a trap number just an error. This is the v1 attempt at integrating mcsafe_copy: https://lists.01.org/pipermail/linux-nvdimm/2016-January/003869.html I think the only change needed is to use static_cpu_has(X86_FEATURE_MCRECOVERY) like so: +static inline int arch_memcpy_from_pmem(void *dst, const void __pmem *src, + size_t n) +{ + if (static_cpu_has(X86_FEATURE_MCRECOVERY)) { + struct mcsafe_ret ret; + + ret = __mcsafe_copy(dst, (void __force *) src, n); + if (ret.remain) + return -EIO; + return 0; + } + memcpy(dst, (void __force *) src, n); + return 0; +} -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org