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=-4.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 64A1CC7618B for ; Wed, 24 Jul 2019 11:48:06 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 3C7B622387 for ; Wed, 24 Jul 2019 11:48:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="VLfavd/H"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="fW20VpN2" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3C7B622387 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:Mime-Version:References:In-Reply-To: Message-Id:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=8AX/+s3xjuDD1YnmSk6F0ldm1Z6kd9SRsJ0Kgf6v8jM=; b=VLfavd/H+YmQzJ r+/ddH3cl9La/2lpVJqzS+z6WNA3oKnQjeVuQnSEvQ1pBMjdASeg7OpiYDfS/LpHzuuZtd9xhrTii fJEcZjFNnsVKg5E/g9MptRTLCOoei/+7BWJZfMZjUE4hrxYMmyIM29LXoz53svCZ4PEDkiEf/jzDr YjCU/0LC3snGx1WKuyeylhMezVzjjC68cup01efDE/8lVwDkOMN/3ySlb5RysSUWJsaY+v+9VioUc 9COVb+B46PlbgZWAxYvwNcx+SUj35xOAODIyPVuShw96T/TR2URqdoVqQECpcHhQ9LNOmV3lq4Y4u 912zQm39/+GQ3pTYVrdA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hqFkU-0000Gu-Ez; Wed, 24 Jul 2019 11:47:58 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1hqFkQ-0000G8-31 for linux-arm-kernel@lists.infradead.org; Wed, 24 Jul 2019 11:47:57 +0000 Received: from devnote2 (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (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 C506122387; Wed, 24 Jul 2019 11:47:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1563968873; bh=mBlNAmlgpbL8sIsWIS0MT/Km8ZKqFPisBuV/zTsyUU4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=fW20VpN2srzvHeaON2aO9PX860hcw585Lgh8gjeSOCIXozBFl1aXstLO3FISoddd2 mCm+LcnzB1FUNo1wCMfGn3zsJWmTU/ozny13dklCz3DHrxCfJ0X7lJM8EndoFPBA7d l8KF7HLC8T2tQa5sTG83bBoq/dkligeH2bI43MP8= Date: Wed, 24 Jul 2019 20:47:48 +0900 From: Masami Hiramatsu To: James Morse Subject: Re: [PATCH v2 3/4] arm64: Make debug exception handlers visible from RCU Message-Id: <20190724204748.94abebef1f184032d2e77f73@kernel.org> In-Reply-To: <0290c71b-6ed3-c455-eb4a-3f6a670f5e37@arm.com> References: <156378170297.12011.17385386326930403235.stgit@devnote2> <156378173770.12011.3832608237079432765.stgit@devnote2> <0290c71b-6ed3-c455-eb4a-3f6a670f5e37@arm.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190724_044756_036427_EBE8E4E7 X-CRM114-Status: GOOD ( 26.37 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Dan Rue , Daniel Diaz , Anders Roxell , Catalin Marinas , Naresh Kamboju , Will Deacon , linux-kernel@vger.kernel.org, Matt Hart , "Paul E . McKenney" , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, 23 Jul 2019 18:07:56 +0100 James Morse wrote: > Hi, > > On 22/07/2019 08:48, Masami Hiramatsu wrote: > > Make debug exceptions visible from RCU so that synchronize_rcu() > > correctly track the debug exception handler. > > > > This also introduces sanity checks for user-mode exceptions as same > > as x86's ist_enter()/ist_exit(). > > > > The debug exception can interrupt in idle task. For example, it warns > > if we put a kprobe on a function called from idle task as below. > > The warning message showed that the rcu_read_lock() caused this > > problem. But actually, this means the RCU is lost the context which > > is already in NMI/IRQ. > > > So make debug exception visible to RCU can fix this warning. > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > > index 9568c116ac7f..a6b244240db6 100644 > > --- a/arch/arm64/mm/fault.c > > +++ b/arch/arm64/mm/fault.c > > @@ -777,6 +777,42 @@ void __init hook_debug_fault_code(int nr, > > debug_fault_info[nr].name = name; > > } > > > > +/* > > + * In debug exception context, we explicitly disable preemption. > > + * This serves two purposes: it makes it much less likely that we would > > + * accidentally schedule in exception context and it will force a warning > > + * if we somehow manage to schedule by accident. > > + */ > > +static void debug_exception_enter(struct pt_regs *regs) > > +{ > > + if (user_mode(regs)) { > > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); > > Would moving entry.S's context_tracking_user_exit() call to be before do_debug_exception() > also fix this? It sounds like treating only user context, correct? This part is just adding assertion, not fixing the problem which Naresh reported. > > I don't know the reason its done 'after' debug exception handling. Its always been like > this: commit 6c81fe7925cc4c42 ("arm64: enable context tracking"). > > > > + } else { > > + /* > > + * We might have interrupted pretty much anything. In > > + * fact, if we're a debug exception, we can even interrupt > > + * NMI processing. > > > + * We don't want in_nmi() to return true, > > + * but we need to notify RCU. > > How come? If you interrupted an SError or pseudo-nmi, it already is. Those paths should > all be painted no-kprobe, but I'm sure there are gaps. The hw-breakpoints can almost > certainly hook them. I think that sentense means "we don't want that this code makes in_nmi() to return true" So, if the breakpoint interrupts pNMI/SError context, it is OK that in_nmi() returns true. > > > > + */ > > + rcu_nmi_enter(); > > Can we interrupt printk()? Do we need printk_nmi_enter()? ... What about ftrace? Good point! As far as I know, we don't use it because ftrace doesn't use printk. But indeed, kprobes user can use printk and they have to call printk_nmi_enter()/exit(), that must be commented in the documentation. Anyway, basically it is user's choice. > > Because SError and pseudo-nmi can interrupt interrupt-masked code, we describe them as > NMI. The only difference here is these exceptions are synchronous. > > > I suspect we should make these debug exceptions nmi for EL1. We can then use this for the > kprobe-re-entrance stuff so the pre/post hooks don't get run if they interrupted something > also described as NMI. I'm not sure how it can prevent... anyway because we have to run a single-stepping for recovery, and kprobe already check the reentered kprobes and skip user-handlers in such case. Thank you, > > > > + } > > + > > + preempt_disable(); > > + > > + /* This code is a bit fragile. Test it. */ > > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "exception_enter didn't work"); > > +} > > +NOKPROBE_SYMBOL(debug_exception_enter); > > > Thanks, > > James -- Masami Hiramatsu _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel