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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 1DB78CCD1A7 for ; Tue, 21 Oct 2025 14:42:49 +0000 (UTC) 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:MIME-Version:Message-ID:Date:References :In-Reply-To:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=lJhMjUhpMY5/q7oE1vONb8rYGdhy+tfa9P/XCuiF90I=; b=pSVcQgdo6jphxk jPpr93xxlY+/jkLGUaj5bEK7KMBRElVhuPBktGBk7tVnMhiMzZe/+tkn1BLzjUs/weN8NZRxxLbmH QyKLsQkFUIk4LcvQo35ziSnFFdL9h+CBKJ1/46427kj/erY7m2wc4ltISMJJX3iLd4ttOl24Kee1H 9//3QciiZJO2NsCHF9tHx6MTGbuJfI4kVQRzrpWpTfHqoX1S0P/A5CumLoVdD9q64En7ab4hmoBSF ACcJoknLuOOUlCdLQ9UisbwW5R7QzX30DaodetgfU6fS8oJtnHemEQi5U4EZGyo+XqHw8qRO7A/e3 6SmlqhIELsX66gFTK0xA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vBDZE-0000000HMW7-1H8A; Tue, 21 Oct 2025 14:42:28 +0000 Received: from galois.linutronix.de ([193.142.43.55]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vBDZB-0000000HMU4-21nt; Tue, 21 Oct 2025 14:42:26 +0000 From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1761057743; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=c27Kz3PCpHpOUA2hxoFAn/lgFIxKWu9eCciI5q0PFVA=; b=1/g8k/vY5UCh/boWPJmgNdB7ubbYE/A/fsOkfq3wSrNQGzQ5valPHvmdpxXGZqcnRroQ58 Bejn39YCg/SlHMeJklk2aBag1ZZ/ZkJkTivx6X2k6zFCy9QlKITW6ujrMH0xoF2co7FakR /dutCEVT+SfKWOjjeaJTqJRMh89jW+zebxPrs6Ff9MEqAR4Jz/7LUbv+E7A5ITdaxbZChA LQsIRW35kAAcwrybohHORnbCHtCEJbOoM88Ok56KpnArXwbr5s8s3yRrxzfqZOWUQSPOoj HHlLFLvQYsl/+KPI+DNPkp5iCy3GtuWwAiSjCg7LL/RU6tt4yt9gYNWiE4WiKA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1761057743; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=c27Kz3PCpHpOUA2hxoFAn/lgFIxKWu9eCciI5q0PFVA=; b=v+qP/IJ72B74NWtVCOdsRXgUn8qUa/Jvf+CPgpV7YyvANjj4e/t31Aew02eNWfxowW2zLI +slcDYUqT+9nxODg== To: David Laight Cc: LKML , Christophe Leroy , Mathieu Desnoyers , Andrew Cooper , Linus Torvalds , kernel test robot , Russell King , linux-arm-kernel@lists.infradead.org, x86@kernel.org, Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , linuxppc-dev@lists.ozlabs.org, Paul Walmsley , Palmer Dabbelt , linux-riscv@lists.infradead.org, Heiko Carstens , Christian Borntraeger , Sven Schnelle , linux-s390@vger.kernel.org, Julia Lawall , Nicolas Palix , Peter Zijlstra , Darren Hart , Davidlohr Bueso , =?utf-8?Q?Andr=C3=A9?= Almeida , Alexander Viro , Christian Brauner , Jan Kara , linux-fsdevel@vger.kernel.org Subject: Re: [patch V3 07/12] uaccess: Provide scoped masked user access regions In-Reply-To: <877bwoz5sp.ffs@tglx> References: <20251017085938.150569636@linutronix.de> <20251017093030.253004391@linutronix.de> <20251020192859.640d7f0a@pumpkin> <877bwoz5sp.ffs@tglx> Date: Tue, 21 Oct 2025 16:42:22 +0200 Message-ID: <874irsz581.ffs@tglx> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251021_074225_655886_3B1C1CF6 X-CRM114-Status: GOOD ( 15.93 ) X-BeenThere: linux-riscv@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-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On Tue, Oct 21 2025 at 16:29, Thomas Gleixner wrote: > On Mon, Oct 20 2025 at 19:28, David Laight wrote: >> There is no requirement to do the accesses in strict memory order >> (or to access the lowest address first). >> The only constraint is that gaps must be significantly less than 4k. > > The requirement is that the access is not spilling over into the kernel > address space, which means: > > USR_PTR_MAX <= address < (1U << 63) > > USR_PTR_MAX on x86 is either > (1U << 47) - PAGE_SIZE (4-level page tables) > or (1U << 57) - PAGE_SIZE (5-level page tables) > > Which means at least ~8 EiB of unmapped space in both cases. > > The access order does not matter at all. I just noticed that LAM reduces that gap to one page, but then the kernel has a 8EiB gap right at the kernel/user boundary, which means even in the LAM case an access with less than 8EiB offset from USR_PTR_MAX is guaranteed to fault and not to be able to speculatively access actual kernel memory. Thanks, tglx _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv