From patchwork Thu May 25 15:51:00 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Howells X-Patchwork-Id: 99096 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:a59:994d:0:b0:3d9:f83d:47d9 with SMTP id k13csp483135vqr; Thu, 25 May 2023 09:07:10 -0700 (PDT) X-Google-Smtp-Source: ACHHUZ7hvKg1eLCgXTqnXCQefZJRxC0oYqekcarZJv2y3fFhKi4Ia/wmZtizZjFdNiJWh3ztVR/G X-Received: by 2002:a05:6a20:7d86:b0:10e:d90f:35d5 with SMTP id v6-20020a056a207d8600b0010ed90f35d5mr5583584pzj.51.1685030830599; Thu, 25 May 2023 09:07:10 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1685030830; cv=none; d=google.com; s=arc-20160816; b=BkKesJAkYbp3iENSuxES2enOGiVBFYLn9sbSdT3UqUFDhcj6vM0qDobOzkCMwpFaxO DdR6gyHaB6LtEuaG6YDsofk1Q0H5QO1qxzg9woH+5pEBp5VbGQxEdYF/WvyJ8vQanY4M W1h+1MMYnC2TgmHqdkDj5q5jfJtx+1nG7ktHk2NGSFe6mQu2Get5QAu7l9Fb52MLa/M5 d3RpWliDEbQuNOdHio8HiiXkkWpZOoAYNFn+O9//Ef+PZ9X3AeuXI3JZOnDpNDeq1ehD KTRLN0eJkS48Me3CVrnlnr0fk7Ajf2ykZ8vKmfrh6cQUJdJYpu4Ixn9ZwwlfKDtA8j3p Uw7g== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-transfer-encoding:mime-version :references:in-reply-to:message-id:date:subject:cc:to:from :dkim-signature; bh=VN2ZrpZ7x9fEyIq82GnRy+FAZ1eh7E2WAh2aAKifPL4=; b=DCws5h9hGmyGLDXaDP4kyyokwuQzpybQt0DZf/nFRDMXhaH/NryiPPEcUtAjwCcJLl qGtIXDJgN5tvpyg3I2S8y07rTQbUhhmo5a+9N7GcSyf9X3KH1caYbqhy+VZM24MzhTdA B7g0mdnVrntyCTKUTDqBou5JiTdkz7g7nk+Cf1BJx3v1yVSosNyDcYE3FInliE49qwrC YQhUyCOnONjUJvCv6yxrOc87+dkiWxW+qVpsvDyoFGJcXFoTkaiOM+WMYEka8gLPf/Ha cx2T5cvcTd2CP0BYNDs0f2tYHJ6DeI5f1Q5nnkMZqUeyd1leddg6J8SiBAH2S/u6IHJc Q6PA== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=JBd9IpDH; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from out1.vger.email (out1.vger.email. [2620:137:e000::1:20]) by mx.google.com with ESMTP id f6-20020a637546000000b0053427b6841dsi58698pgn.337.2023.05.25.09.06.54; Thu, 25 May 2023 09:07:10 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=JBd9IpDH; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241726AbjEYPwV (ORCPT + 99 others); Thu, 25 May 2023 11:52:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41406 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241592AbjEYPwG (ORCPT ); Thu, 25 May 2023 11:52:06 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 85AFB197 for ; Thu, 25 May 2023 08:51:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1685029876; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VN2ZrpZ7x9fEyIq82GnRy+FAZ1eh7E2WAh2aAKifPL4=; b=JBd9IpDHLV+EuM1hF8Dgyn4tW0k1HXqy/FmZa7cTvJkRauIcaYkNTFhx2Gw1fjmxYKZtcW AQWKDQi31wEMxOz0SjwOf2X2SxvyGYidUPlgEbNraQF/KdFw1mfR1DAbXQpNLnkcjovie3 hA9nJJMCVeSXHBFMmGWtoB4XZ445yh0= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-554-FDn4oHLSPcWua6K8xvmmRA-1; Thu, 25 May 2023 11:51:11 -0400 X-MC-Unique: FDn4oHLSPcWua6K8xvmmRA-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 9B8FF85A5AA; Thu, 25 May 2023 15:51:10 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.39.192.68]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3BEA6492B0A; Thu, 25 May 2023 15:51:08 +0000 (UTC) From: David Howells To: Christoph Hellwig , David Hildenbrand Cc: David Howells , Jens Axboe , Al Viro , Matthew Wilcox , Jan Kara , Jeff Layton , Jason Gunthorpe , Logan Gunthorpe , Hillf Danton , Christian Brauner , Linus Torvalds , linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton Subject: [RFC PATCH 1/3] mm: Don't pin ZERO_PAGE in pin_user_pages() Date: Thu, 25 May 2023 16:51:00 +0100 Message-Id: <20230525155102.87353-2-dhowells@redhat.com> In-Reply-To: <20230525155102.87353-1-dhowells@redhat.com> References: <20230525155102.87353-1-dhowells@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_NONE,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1766882888017128645?= X-GMAIL-MSGID: =?utf-8?q?1766882888017128645?= Make pin_user_pages*() leave the ZERO_PAGE unpinned if it extracts a pointer to it from the page tables and make unpin_user_page*() correspondingly ignore the ZERO_PAGE when unpinning. We don't want to risk overrunning the zero page's refcount as we're only allowed ~2 million pins on it - something that userspace can conceivably trigger. Signed-off-by: David Howells cc: Christoph Hellwig cc: David Hildenbrand cc: Andrew Morton cc: Jens Axboe cc: Al Viro cc: Matthew Wilcox cc: Jan Kara cc: Jeff Layton cc: Jason Gunthorpe cc: Logan Gunthorpe cc: Hillf Danton cc: Christian Brauner cc: Linus Torvalds cc: linux-fsdevel@vger.kernel.org cc: linux-block@vger.kernel.org cc: linux-kernel@vger.kernel.org cc: linux-mm@kvack.org --- mm/gup.c | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-) diff --git a/mm/gup.c b/mm/gup.c index bbe416236593..d2662aa8cf01 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -51,7 +51,8 @@ static inline void sanity_check_pinned_pages(struct page **pages, struct page *page = *pages; struct folio *folio = page_folio(page); - if (!folio_test_anon(folio)) + if (page == ZERO_PAGE(0) || + !folio_test_anon(folio)) continue; if (!folio_test_large(folio) || folio_test_hugetlb(folio)) VM_BUG_ON_PAGE(!PageAnonExclusive(&folio->page), page); @@ -131,6 +132,13 @@ struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags) else if (flags & FOLL_PIN) { struct folio *folio; + /* + * Don't take a pin on the zero page - it's not going anywhere + * and it is used in a *lot* of places. + */ + if (page == ZERO_PAGE(0)) + return page_folio(ZERO_PAGE(0)); + /* * Can't do FOLL_LONGTERM + FOLL_PIN gup fast path if not in a * right zone, so fail and let the caller fall back to the slow @@ -180,6 +188,8 @@ struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags) static void gup_put_folio(struct folio *folio, int refs, unsigned int flags) { if (flags & FOLL_PIN) { + if (folio == page_folio(ZERO_PAGE(0))) + return; node_stat_mod_folio(folio, NR_FOLL_PIN_RELEASED, refs); if (folio_test_large(folio)) atomic_sub(refs, &folio->_pincount); @@ -224,6 +234,13 @@ int __must_check try_grab_page(struct page *page, unsigned int flags) if (flags & FOLL_GET) folio_ref_inc(folio); else if (flags & FOLL_PIN) { + /* + * Don't take a pin on the zero page - it's not going anywhere + * and it is used in a *lot* of places. + */ + if (page == ZERO_PAGE(0)) + return 0; + /* * Similar to try_grab_folio(): be sure to *also* * increment the normal page refcount field at least once, @@ -3079,6 +3096,9 @@ EXPORT_SYMBOL_GPL(get_user_pages_fast); * * FOLL_PIN means that the pages must be released via unpin_user_page(). Please * see Documentation/core-api/pin_user_pages.rst for further details. + * + * Note that if the zero_page is amongst the returned pages, it will not have + * pins in it and unpin_user_page() will not remove pins from it. */ int pin_user_pages_fast(unsigned long start, int nr_pages, unsigned int gup_flags, struct page **pages) @@ -3161,6 +3181,9 @@ EXPORT_SYMBOL(pin_user_pages); * pin_user_pages_unlocked() is the FOLL_PIN variant of * get_user_pages_unlocked(). Behavior is the same, except that this one sets * FOLL_PIN and rejects FOLL_GET. + * + * Note that if the zero_page is amongst the returned pages, it will not have + * pins in it and unpin_user_page() will not remove pins from it. */ long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages, struct page **pages, unsigned int gup_flags)