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 145E4CCA47A for ; Thu, 2 Jun 2022 16:47:42 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A7DC56B0071; Thu, 2 Jun 2022 12:47:41 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A28F76B0073; Thu, 2 Jun 2022 12:47:41 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8EFC16B0074; Thu, 2 Jun 2022 12:47:41 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 80DFE6B0071 for ; Thu, 2 Jun 2022 12:47:41 -0400 (EDT) Received: from smtpin23.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 588D52157F for ; Thu, 2 Jun 2022 16:47:41 +0000 (UTC) X-FDA: 79533877122.23.5AB3B2E Received: from mga12.intel.com (mga12.intel.com [192.55.52.136]) by imf29.hostedemail.com (Postfix) with ESMTP id A9D12120057 for ; Thu, 2 Jun 2022 16:47:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1654188460; x=1685724460; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=A8LiKaAE36i4kEOLQiMiWUcBtJI+3DyK4ToZlO6mza8=; b=mrlQE2ZCYCd/GHMTZ30QE4JCbOY08nxj0xFAle02S38nuh1cIqbqLh6W zIsg8b5Q6ENqJGJNuR4r/Cx6xemkQ/IKfG9jVRJKIlGLy/Xn1aTDU7U5E ZP5yCyR9KOu6OVVKpsO3/DpencR6UZ5+TFrKN5YmrpucSa8PWKiY9UC2Q muUUULiKpUQMoaHTdQ1U+uvCZoqcN3zGNCpt9CXP5N09TfED0JgeycNkQ BX22eJuTCbeota8/Acjkzn1J/SuSKMtfiq4WLIbpTURjSpGiOqYH6F9RG fWxqizuk4phtMdMDALfA7ZbGYQquPmDczsh1wOhQ/WapGqwOoD2iEzozI Q==; X-IronPort-AV: E=McAfee;i="6400,9594,10366"; a="255871761" X-IronPort-AV: E=Sophos;i="5.91,271,1647327600"; d="scan'208";a="255871761" Received: from orsmga007.jf.intel.com ([10.7.209.58]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Jun 2022 09:47:36 -0700 X-IronPort-AV: E=Sophos;i="5.91,271,1647327600"; d="scan'208";a="577592309" Received: from bkakkar-mobl1.amr.corp.intel.com (HELO [10.212.249.147]) ([10.212.249.147]) by orsmga007-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Jun 2022 09:47:35 -0700 Message-ID: <1f0fd9f4-295f-6b44-47ff-b6b56892e680@intel.com> Date: Thu, 2 Jun 2022 09:47:33 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1 Subject: Re: Is _PAGE_PROTNONE set only for user mappings? Content-Language: en-US To: Hyeonggon Yoo <42.hyeyoo@gmail.com> Cc: Mel Gorman , Tom Lendacky , Rick Edgecombe , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , "Kirill A. Shutemov" , Tianyu Lan , "Aneesh Kumar K.V" , linux-kernel@vger.kernel.org, linux-mm@kvack.org, vbabka@suse.cz, akpm@linux-foundation.org, willy@infradead.org References: <20220506051940.156952-1-42.hyeyoo@gmail.com> <56f89895-601e-44c9-bda4-5fae6782e27e@amd.com> <5fe161cb-6c55-6c4d-c208-16c77e115d3f@amd.com> <8c2735ac-0335-6e2a-8341-8266d5d13c30@intel.com> <20220512103748.GH3441@techsingularity.net> <3f2f7c09-ddf3-6052-9860-8554a4ff2798@intel.com> From: Dave Hansen In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=mrlQE2ZC; dmarc=pass (policy=none) header.from=intel.com; spf=none (imf29.hostedemail.com: domain of dave.hansen@intel.com has no SPF policy when checking 192.55.52.136) smtp.mailfrom=dave.hansen@intel.com X-Stat-Signature: fbhstt1cted4j1k68hmusydpf3ci1wec X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: A9D12120057 X-HE-Tag: 1654188446-5876 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 5/29/22 03:32, Hyeonggon Yoo wrote: > On Mon, May 16, 2022 at 07:04:32AM -0700, Dave Hansen wrote: > Writing code I'm a bit confused: > commit d1440b23c922d8 ("x86/mm: Factor out pageattr > _PAGE_GLOBAL setting") says: > > "This unconditional setting of _PAGE_GLOBAL is a problem when we have > PTI and non-PTI and we want some areas to have _PAGE_GLOBAL and some > not." > > Is this this sentence not valid anymore in PTI, > and just unconditionally setting _PAGE_GLOBAL would be okay in kernel > side regardless of PTI? I believe it's still valid. IIRC, there are three cases: 1. No KPTI. All kernel mappings are _PAGE_GLOBAL. Basically, for present mappings, if _PAGE_USER is clear, _PAGE_GLOBAL is set. 2. KPTI with PCID hardware support (or in a few other cases): The kernel image is mostly non-global. Anything mapped into userspace *is* marked global, like entry text. 3. KPTI without PCIDs: Basically case #2, but with more of the kernel image left global. So, not only are there different KPTI modes, there a different pars of the kernel that require different _PAGE_GLOBAL behavior. pti_kernel_image_global_ok() in arch/x86/mm/pti.c explains it pretty well.