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=-3.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED,USER_AGENT_NEOMUTT autolearn=ham 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 697A3C43381 for ; Fri, 29 Mar 2019 12:22:39 +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 379552082F for ; Fri, 29 Mar 2019 12:22:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="HIOhNbm4" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 379552082F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com 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:In-Reply-To:MIME-Version:References: 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=VBlRW8kFgFU9H6PFJUEuSNTITgr6rrFrbJjdLpySwas=; b=HIOhNbm4tWvVX6 JGiR6lGEoIRKkhVsuarvp10gNXapR0xKevbWaRL/JQGsYXnPG6pOtpXZPlPgn1914t2UNyS1I3rEf Emti2dXAA5PDoulQRfw+p0olQMmgDpTLmJ+GfR/HPZ7vb0M/2+PvJIvDdwgituG1Gdu2tKBvWwEW8 pGslMVV8raOc9uvt0SzCapHWwXpEJuS/Xy+QiShjg6n0/wgRmcIs55ixpGXJbNt0wCWo46waC5ZIs 8d8Iw3QKi6C825+WozoxYq0/Xgql4+AFeSCUuTtf3Bv5hYgQEWm3D0JSYUQ4q2CDinStpp2ymYp3F b1vfML8k4caKGj96bKKQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1h9qWn-0000zj-0l; Fri, 29 Mar 2019 12:22:33 +0000 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70] helo=foss.arm.com) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1h9qWc-0000o6-0u for linux-arm-kernel@lists.infradead.org; Fri, 29 Mar 2019 12:22:25 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id AA12815BF; Fri, 29 Mar 2019 05:22:20 -0700 (PDT) Received: from mbp (usa-sjc-mx-foss1.foss.arm.com [217.140.101.70]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 668B93F575; Fri, 29 Mar 2019 05:22:19 -0700 (PDT) Date: Fri, 29 Mar 2019 12:22:16 +0000 From: Catalin Marinas To: Vincenzo Frascino Subject: Re: [PATCH 4/5] arm64: compat: Add KUSER_HELPERS config option Message-ID: <20190329122216.xa6va62qwyynoldt@mbp> References: <20190319151542.19557-1-vincenzo.frascino@arm.com> <20190319151542.19557-5-vincenzo.frascino@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190319151542.19557-5-vincenzo.frascino@arm.com> User-Agent: NeoMutt/20170113 (1.7.2) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190329_052222_647619_AD29A681 X-CRM114-Status: GOOD ( 17.11 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, Mark Rutland , Will Deacon , linux-arm-kernel@lists.infradead.org, Jann Horn 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, Mar 19, 2019 at 03:15:41PM +0000, Vincenzo Frascino wrote: > When kuser helpers are enabled the kernel maps the relative code at > a fixed address (0xffff0000). Making configurable the option to disable > them means that the kernel can remove this mapping and any access to > this memory area results in a sigfault. > > Add a KUSER_HELPERS config option that can be used to disable the > mapping when it is turned off. > > This option can be turned off if and only if the applications are > designed specifically for the platform and they do not make use of the > kuser helpers code. > > Note: kuser helpers is disabled by default with 64K pages. Actually this last sentence is more than just the default y/n for this option. It adds a hard dependency, which means it cannot be enabled. Currently we do allow COMPAT with 64K pages if EXPERT. Is the main reason for this just to be able to subtract PAGE_SIZE for TASK_SIZE_32 in the last patch? What happens if we leave TASK_SIZE_32 set to 0x100000000 for the 64K page configuration? Do we still have the C99 issue mentioned in the cover letter (assuming that the last page is already occupied by the vectors page)? -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel