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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4691DC43334 for ; Sat, 18 Jun 2022 11:35:57 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 46ABB6B0071; Sat, 18 Jun 2022 07:35:56 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 419706B0072; Sat, 18 Jun 2022 07:35:56 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2E13F6B0073; Sat, 18 Jun 2022 07:35:56 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 200406B0071 for ; Sat, 18 Jun 2022 07:35:56 -0400 (EDT) Received: from smtpin15.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id D832F351EE for ; Sat, 18 Jun 2022 11:35:55 +0000 (UTC) X-FDA: 79591152270.15.CB4B96D Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf11.hostedemail.com (Postfix) with ESMTP id 994A440009 for ; Sat, 18 Jun 2022 11:35:54 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A0510113E; Sat, 18 Jun 2022 04:35:53 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E864F3F7D8; Sat, 18 Jun 2022 04:35:49 -0700 (PDT) Date: Sat, 18 Jun 2022 12:35:35 +0100 From: Mark Rutland To: Tong Tiangen Cc: James Morse , Andrew Morton , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Robin Murphy , Dave Hansen , Catalin Marinas , Will Deacon , Alexander Viro , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , x86@kernel.org, "H . Peter Anvin" , linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Kefeng Wang , Xie XiuQi , Guohanjun Subject: Re: [PATCH -next v5 7/8] arm64: add uaccess to machine check safe Message-ID: References: <20220528065056.1034168-1-tongtiangen@huawei.com> <20220528065056.1034168-8-tongtiangen@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf11.hostedemail.com: domain of mark.rutland@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=mark.rutland@arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1655552155; h=from:from:sender: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:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Kk2yQqwadyskZRkrcZju7N+T1vnhEJeDZpD1iabnjfI=; b=PyFvTLaIlKDyOHJJRRU8qDvNm2WmwzfAuq/FkTsGQwnFU049ysentlzQvFC3uY7l6HY6ne WCAqWN04ikAf5MHKHj8EFCqEJAFGJZ8fZ7aFG5h8dzPUB1IeNbB22BawfYOoX3yLA4715a 8fUMYt/xAdCsDaMiyLhDVTQ47dnn4Xw= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1655552155; a=rsa-sha256; cv=none; b=Y/KLwD5uEo8riJLRaupvxbfYrxzpDKxuDnX3VH6G8hVKSc1gnZbgPZD6aAp4ghWzd2kO0k vO3TW2BTdGQKuBOXGO9ETl5fRjjjXo5Ogk4VEKbKoTfWtGMa/TBF8garoa9+A3PB8JJ/Y/ 9mg8lyHDI6kHp3RlxQbxTWiIDJ4n1Sk= X-Stat-Signature: 36d5dic4fw3zxy11y774ggdgx1ziphhx X-Rspamd-Queue-Id: 994A440009 X-Rspam-User: Authentication-Results: imf11.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf11.hostedemail.com: domain of mark.rutland@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=mark.rutland@arm.com X-Rspamd-Server: rspam10 X-HE-Tag: 1655552154-885161 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sat, Jun 18, 2022 at 05:27:45PM +0800, Tong Tiangen wrote: > > > 在 2022/6/17 17:06, Mark Rutland 写道: > > On Sat, May 28, 2022 at 06:50:55AM +0000, Tong Tiangen wrote: > > > If user access fail due to hardware memory error, only the relevant > > > processes are affected, so killing the user process and isolate the > > > error page with hardware memory errors is a more reasonable choice > > > than kernel panic. > > > > > > Signed-off-by: Tong Tiangen > > > > > --- > > > arch/arm64/lib/copy_from_user.S | 8 ++++---- > > > arch/arm64/lib/copy_to_user.S | 8 ++++---- > > > > All of these changes are to the *kernel* accesses performed as part of copy > > to/from user, and have nothing to do with userspace, so it does not make sense > > to mark these as UACCESS. > > You have a point. so there is no need to modify copy_from/to_user.S in this > patch set. Cool, thanks. If this patch just has the extable change, that's fine by me. > > Do we *actually* need to recover from failues on these accesses? Looking at > > _copy_from_user(), the kernel will immediately follow this up with a memset() > > to the same address which will be fatal anyway, so this is only punting the > > failure for a few instructions. > > If recovery success, The task will be killed and there will be no subsequent > memset(). I don't think that's true. IIUC per the last patch, in the exception handler we'll apply the fixup then force a signal. That doesn't kill the task immediately, and we'll return from the exception handler back into the original context (with the fixup applied). The structure of copy_from_user() is copy_from_user(to, from, n) { _copy_from_user(to, from, n) { res = n; res = raw_copy_from_user(to, from, n); if (res) memset(to + (n - res), 0, res); } } So when the fixup is applied and res indicates that the copy terminated early, there is an unconditinal memset() before the fatal signal is handled in the return to userspace path. > > If we really need to recover from certain accesses to kernel memory we should > > add a new EX_TYPE_KACCESS_ERR_ZERO_MC or similar, but we need a strong > > rationale as to why that's useful. As things stand I do not beleive it makes > > sense for copy to/from user specifically. [...] > > > diff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c > > > index c301dcf6335f..8ca8d9639f9f 100644 > > > --- a/arch/arm64/mm/extable.c > > > +++ b/arch/arm64/mm/extable.c > > > @@ -86,10 +86,10 @@ bool fixup_exception_mc(struct pt_regs *regs) > > > if (!ex) > > > return false; > > > - /* > > > - * This is not complete, More Machine check safe extable type can > > > - * be processed here. > > > - */ > > > + switch (ex->type) { > > > + case EX_TYPE_UACCESS_ERR_ZERO: > > > + return ex_handler_uaccess_err_zero(ex, regs); > > > + } > > > > This addition specifically makes sense to me, so can you split this into a separate patch? > > According to my understanding of the above, only the modification of > extable.c is retained. > > So what do you mean which part is made into a separate patch? As above, if you just retain the extable.c changes, that's fine by me. Thanks, Mark.