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 B78F2C7619A for ; Wed, 5 Apr 2023 15:15:20 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 2B14C6B0072; Wed, 5 Apr 2023 11:15:20 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 261B96B0074; Wed, 5 Apr 2023 11:15:20 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 103236B0075; Wed, 5 Apr 2023 11:15:20 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 0073F6B0072 for ; Wed, 5 Apr 2023 11:15:19 -0400 (EDT) Received: from smtpin30.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id B35991C6D9B for ; Wed, 5 Apr 2023 15:15:19 +0000 (UTC) X-FDA: 80647685958.30.2097C80 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf26.hostedemail.com (Postfix) with ESMTP id 3ADB8140011 for ; Wed, 5 Apr 2023 15:15:17 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=PXgGVFyE; spf=pass (imf26.hostedemail.com: domain of peterx@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1680707717; a=rsa-sha256; cv=none; b=7V3aUObIyqnUu2OSlRWAqTGZld5OPV8ULWhot67BFyzeg5MeBNeReb9iBwFkLPti+px0Mq SD/uJeaBE9cVNIPCNYrmiyBrQQ/Acc/wKN08uq1kEnHPoOBn6hzitwFuoMcLmbXHGikklP h9fesKnDaDD0EslQeIv/yy8zEGoCEIs= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=PXgGVFyE; spf=pass (imf26.hostedemail.com: domain of peterx@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1680707717; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=ZCSaElfv8AUmPjWD9J2bsaS+EBjnAjuOP3qTK8N+O8U=; b=WJt2ImV5O0+sgLawwlNVvIXUR+a9nwvZ2Y/vsp4bbfK1vOCzcGGrPqezLnJOwS6wtCpCvT 6mh5nR+c/vgjJ2QcOqX3ugfm63f9G6k1hk1j9Tk6mF7/hYfRVbSweldt6C2AAmd5uShVdd azjJbt9Bn8W7BaNgekYvYTWP8FUwZHQ= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1680707716; 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=ZCSaElfv8AUmPjWD9J2bsaS+EBjnAjuOP3qTK8N+O8U=; b=PXgGVFyEFwzFrIAYr9B6SXjQj0VbD92Kyt+rcIkhaSEsceJyIlwR3MK6hf43CG1wAqPWAl mKqVAySmqch9f1XHXd3CDMMVaBThHeUod0o4bUKk9+SS4jcW5ld/ltaFOT3raQZYp45v76 nyN8RiFm8oVkz5HpSBumzj+GzXpxh7I= Received: from mail-qt1-f198.google.com (mail-qt1-f198.google.com [209.85.160.198]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-113-FAu2manvOemtz4qyzLkf1A-1; Wed, 05 Apr 2023 11:15:15 -0400 X-MC-Unique: FAu2manvOemtz4qyzLkf1A-1 Received: by mail-qt1-f198.google.com with SMTP id d75a77b69052e-3e1522cf031so12190411cf.1 for ; Wed, 05 Apr 2023 08:15:15 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680707715; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=ZCSaElfv8AUmPjWD9J2bsaS+EBjnAjuOP3qTK8N+O8U=; b=HUp0IpO1OaGDjYGnsVkopm/jXxtCWwaOqyL5prUkvZaHl+IY65qhyXpLvZGLJsuUaE QPpD4hd/tMKlCmj2almxAloPgSBzm5ZqKS/36Db4lVBWotZTFe5kdzaV/yiC8Sw6QDpr KnswZFlK2fz34HeNr/AYK59xTOBaZpTyCXosgxmmaIL7O5UyBQRClxOK0+ulXP5fos4r z6x492BreME8zHKLRTdjhwXqNrNBTM0C2C4hL1xqDAc0x8tzMUPsUuTRJC7kFVkdzvel 5fw2iHzwaNyfxIEhMlDmNbqxkhSup6eEcSrAnQocX5NECTLJqbWwFnIu30HjTBx/uTza 7Xqg== X-Gm-Message-State: AAQBX9ffZUXGz/qDYi5zJ8WyEmThPsJoRB1QZR+55QbZUiJtrpWQ9khs pAdJpvGaa0zkzCfgzjCK5b4BLlK39fZyPfc+3fDjS/CjX0xkS05SL/2zgOoPovjooOoPbXK5GlU 48f0KWH4Fs6c= X-Received: by 2002:a05:622a:1ba8:b0:3e3:98cf:68ae with SMTP id bp40-20020a05622a1ba800b003e398cf68aemr6761945qtb.2.1680707714565; Wed, 05 Apr 2023 08:15:14 -0700 (PDT) X-Google-Smtp-Source: AKy350amPFJ+bM/0v8906JhqvyF31P/2ETS/KzMuu4Tg0eaX0KiKrrhsvKyctDwRDtf6mNRyFAbQUw== X-Received: by 2002:a05:622a:1ba8:b0:3e3:98cf:68ae with SMTP id bp40-20020a05622a1ba800b003e398cf68aemr6761866qtb.2.1680707713888; Wed, 05 Apr 2023 08:15:13 -0700 (PDT) Received: from x1n (bras-base-aurron9127w-grc-40-70-52-229-124.dsl.bell.ca. [70.52.229.124]) by smtp.gmail.com with ESMTPSA id z24-20020ac84558000000b003d7e923736asm4096162qtn.6.2023.04.05.08.15.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 05 Apr 2023 08:15:13 -0700 (PDT) Date: Wed, 5 Apr 2023 11:15:12 -0400 From: Peter Xu To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Muhammad Usama Anjum Subject: Re: [PATCH v1 2/2] mm/userfaultfd: don't consider uffd-wp bit of writable migration entries Message-ID: References: <20230405142535.493854-1-david@redhat.com> <20230405142535.493854-3-david@redhat.com> MIME-Version: 1.0 In-Reply-To: <20230405142535.493854-3-david@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspam-User: X-Rspamd-Queue-Id: 3ADB8140011 X-Rspamd-Server: rspam01 X-Stat-Signature: pg1h6yfu1zonaqsj9kgy6driu3atkutz X-HE-Tag: 1680707717-306176 X-HE-Meta: U2FsdGVkX18cPYHBBWIgUa8FrbmRRNlmOSHtA6ZQ4NcTVUj613iJSl5R42DgqlFacrm1ghERl80R4it3o1jnLrSzqp/BE9Vd5z6XhLkaawuVjFITZWHuy/tRzP1k4oqAVdaL9n4poX5zyT5Ca/xqBvxLVFeghMXLQbWTdDTEg4uyITwPrDC7haonc4KbnSIb983LrPNbbK7SH3XNnYhC35X/GZVRO8PtoWCZ7qQ/tGFlXIVSrysVkbaIjNU2ShFIou1NqBZ4iJP75oBqdzrNEEtKUUuYiQdrqKHOuqJfDYpKyW2rvobX/mRPJuXHvZBRdJfBqPo/HfpUOoO+gkKUpj3xd7+P33qOMbAXkqOUcykaIPS7oqHPhTfc8bieKpYtZ9Tu+CZ16d3hTdgLFKxdhPDDBe5PoUcU50xMVY8/DCKDc5iOFA7yHmkpdAht+vFjZaKc1uIoGO/z/u1qBrgnGDdY/sMwoiWbkWiDkJdynvZ24rbP5TEKMIU7Vz9vet6M6pHSEb0X9zKlufbAYFte13ITYlUcBqHCd+XqhR+Nkk8l5r5a+qh3x6gAjrg4BINPo14JBSsjQBME3GCiMhiKgFTWT7I2DfzMH4C+wuFwzhsiEw91TfaQ544pGwBUmpg1jP1JLUX/zVvT1pxj0FlTH743VCbXuqX0WjiZ8PX/u4GgKW/5thV3c088HFf9iwVPQjCFcfaeDVrlkAQz3rvx+aaAD11KXQCTsH7Yi+nj29l8nxw/3RtX6uqUlLRTRq+UN2uU/ElvsnPEyAla+oYX5Q0NUIdUNB6WNhFPo8GkLkdUWw8fBaoVNyTFDbS0pBXDSDq3IHJhP33o6bnIzx8QvyE9JgPpI7+41bSUFzYURll5TUh6d2btTeo3dldc+KuC2VDgMur9HCaGJvJJa6/uE6thkdEENal1VVC6L5vvy7BwXGtoTmFxJu0ZMJPEiKPKeCFIQx6pHMTwDikZwqx rs/TdU3c XOqFyRV6S/od36mtQDUMZAax3u8V4f73xuzfzlY8WJFLJt6BSwddeSvDlsejGzCI3BoUa9rECDT/Qy+M5Sh0cyggqC02U0RnZyraOl+aNqD6bVbZxS5RRbGjP1EWcsCvQU/Na1psRXU46dSwtLJNSLWFEGuGvgFW7syjvidj1MTYTVCzZBMXRIym2ryXG55/GTumsnda1FpnX4tbyw48NqMoH4qh97gbfgxIR4OBr+mO5pUGdf8COPy60rwWHkhIyRGx+q5njWhV99c7yGWLE/CEAmCLF+yl3/45uF02jBNWQtm5RlxRWslZ1tsHF+GLFGQS0v0lzeOyBiSBSk6/1TLtqCHSemSt4oJSV0KuCgcqpz7JTNRZjJW9ObFVmIROHMe9PssvwqemkAKLeDlPmCOmWGg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000081, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Apr 05, 2023 at 04:25:35PM +0200, David Hildenbrand wrote: > If we end up with a writable migration entry that has the uffd-wp bit set, > we already messed up: the source PTE/PMD was writable, which means we could > have modified the page without notifying uffd first. Setting the uffd-wp > bit always implies converting migration entries to !writable migration > entries. > > Commit 8f34f1eac382 ("mm/userfaultfd: fix uffd-wp special cases for > fork()") documents that "3. Forget to carry over uffd-wp bit for a write > migration huge pmd entry", but it doesn't really say why that should be > relevant. > > So let's remove that code to avoid hiding an eventual underlying issue > (in the future, we might want to warn when creating writable migration > entries that have the uffd-wp bit set -- or even better when turning a > PTE writable that still has the uffd-wp bit set). > > This now matches the handling for hugetlb migration entries in > hugetlb_change_protection(). > > In copy_huge_pmd()/copy_nonpresent_pte()/copy_hugetlb_page_range(), we > still transfer the uffd-bit also for writable migration entries, but simply > because we have unified handling for "writable" and "readable-exclusive" > migration entries, and we care about transferring the uffd-wp bit for > the latter. > > Signed-off-by: David Hildenbrand Reviewed-by: Peter Xu I think that's mostly for sanity to carry over one generic bit between present <-> !present, even if uffd-wp is not that generic and currently closely bound to write bit. E.g., we will need to be more careful when we want to change the meaning of uffd-wp bit some day, but that'll always be challenging anyway, so not something this will change. Thanks, -- Peter Xu