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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 327A0C0044C for ; Tue, 6 Nov 2018 00:35:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EEAD420827 for ; Tue, 6 Nov 2018 00:35:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EEAD420827 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-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729184AbeKFJ5k (ORCPT ); Tue, 6 Nov 2018 04:57:40 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:53636 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725839AbeKFJ5k (ORCPT ); Tue, 6 Nov 2018 04:57:40 -0500 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 B078E80D; Mon, 5 Nov 2018 16:35:14 -0800 (PST) Received: from brain-police (usa-sjc-mx-foss1.foss.arm.com [217.140.101.70]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 62F513F718; Mon, 5 Nov 2018 16:35:14 -0800 (PST) Date: Tue, 6 Nov 2018 00:35:10 +0000 From: Will Deacon To: Anshuman Khandual Cc: Andrea Arcangeli , Zi Yan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kirill.shutemov@linux.intel.com, akpm@linux-foundation.org, mhocko@suse.com, Naoya Horiguchi Subject: Re: [PATCH] mm/thp: Correctly differentiate between mapped THP and PMD migration entry Message-ID: <20181106003509.GA27283@brain-police> References: <1539057538-27446-1-git-send-email-anshuman.khandual@arm.com> <7E8E6B14-D5C4-4A30-840D-A7AB046517FB@cs.rutgers.edu> <84509db4-13ce-fd53-e924-cc4288d493f7@arm.com> <1968F276-5D96-426B-823F-38F6A51FB465@cs.rutgers.edu> <5e0e772c-7eef-e75c-2921-e80d4fbe8324@arm.com> <2398C491-E1DA-4B3C-B60A-377A09A02F1A@cs.rutgers.edu> <20181017020930.GN30832@redhat.com> <9d9aaf03-617a-d383-7d59-8b98fdd3c1e7@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9d9aaf03-617a-d383-7d59-8b98fdd3c1e7@arm.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 02, 2018 at 11:45:00AM +0530, Anshuman Khandual wrote: > On 10/17/2018 07:39 AM, Andrea Arcangeli wrote: > > What we need to do during split is an invalidate of the huge TLB. > > There's no pmd_trans_splitting anymore, so we only clear the present > > bit in the PTE despite pmd_present still returns true (just like > > PROT_NONE, nothing new in this respect). pmd_present never meant the > > On arm64, the problem is that pmd_present() is tied with pte_present() which > checks for PTE_VALID (also PTE_PROT_NONE) but which gets cleared during PTE > invalidation. pmd_present() returns false just after the first step of PMD > splitting. So pmd_present() needs to be decoupled from PTE_VALID which is > same as PMD_SECT_VALID and instead should depend upon a pte bit which sticks > around like PAGE_PSE as in case of x86. I am working towards a solution. Could we not just go via a PROT_NONE mapping during the split, instead of having to allocate a new software bit to treat these invalid ptes as present? Will