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=-4.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 3B92DC432BE for ; Tue, 31 Aug 2021 17:46:03 +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 07E0B6103A for ; Tue, 31 Aug 2021 17:46:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 07E0B6103A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc: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=ILJDYtZI+NJ+nyhMR8D2CevRN4/9U0aJTWHDb537IG8=; b=pA/NCVnGxnX24j ouxKcndH1AEhpfCt+rbUJYUtnrmNcdN7wfrS8bL8wSvZ/M0gJsQfQkBs07dhh4O8xWnlJUIlwLqIS jqvyCJkGEJPlrXliBWAoGkYg6i27AVAiFGO5kW5nyNelVeyU+BN1uUsjZ4NUVM9T3Rv8Q1aCwAWj3 7pv2G0EnMkpj+8ImCc5QrPB9ywgSOGo0vWf4k257xnAHrOWtjsQ+1t8s49uoGYXWK+zKvkDByT9pl Raw5yM2+Uhacd3SFkG3nwWVfF+1QqBLA1AL1yaw/nJ6IMfet06HtkccsvcJFHTiUoFFUTYdwayU0G AtpERNeggSyiKYvwGwhQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mL7o5-002qGf-U7; Tue, 31 Aug 2021 17:44:22 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mL7o2-002qG9-AA for linux-arm-kernel@lists.infradead.org; Tue, 31 Aug 2021 17:44:19 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id D92EB6101B; Tue, 31 Aug 2021 17:44:16 +0000 (UTC) Date: Tue, 31 Aug 2021 18:44:14 +0100 From: Catalin Marinas To: Benjamin Herrenschmidt Cc: linux-arm-kernel@lists.infradead.org, Will Deacon , benh@amazon.com, Szabolcs Nagy , Mark Brown Subject: Re: ucontext, kernel vs. userspace (glibc) Message-ID: References: <131d684ea46de6330ab90532ab73729d6c0690bd.camel@kernel.crashing.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <131d684ea46de6330ab90532ab73729d6c0690bd.camel@kernel.crashing.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210831_104418_407659_0A770846 X-CRM114-Status: GOOD ( 15.66 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Ben, On Mon, Aug 30, 2021 at 08:40:03PM +1000, Benjamin Herrenschmidt wrote: > So I'm discovering arm64 intricacies and today, as I was looking at SVE > support (in the context of distro glibc backports.. don't ask), I > noticed that glibc has no provision for dealing with kernel generated > ucontext's in its {get,set,swap}_context functions... > > (It says so explicitly in the code unless I misunderstood). > > So one thing we did to "solve" this on ppc64 a while ago was to create > a swapcontext syscall which can operate as all 3 operations (you can > have NULL arguments), which also handles the sigprocmask (bonus: > atomically with the context get/set from a userspace perspective). > > Would it make sense to do something similar on aarch64 ? (And have > glibc then exploit it). > > The hard-to-solve thing is the case where the SVE context spills > outside of the ucontext itself, in the extra room on the stack, since > programs that "now" about ucontext will not have allocated space for > that, so that's more/less a lost cause already. I haven't fully parsed your email yet but adding a Mark B for SVE and Szabolcs for glibc (and removing Dave who left Arm recently). -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel