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=-9.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable 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 CB5D5C43381 for ; Thu, 14 Feb 2019 00:06:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8EBC9218FF for ; Thu, 14 Feb 2019 00:06:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="rq32CuBk" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404564AbfBNAGd (ORCPT ); Wed, 13 Feb 2019 19:06:33 -0500 Received: from userp2120.oracle.com ([156.151.31.85]:48432 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1733027AbfBNAGd (ORCPT ); Wed, 13 Feb 2019 19:06:33 -0500 Received: from pps.filterd (userp2120.oracle.com [127.0.0.1]) by userp2120.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x1DNxBhK099616; Thu, 14 Feb 2019 00:02:27 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : in-reply-to : references; s=corp-2018-07-02; bh=sphrv7BG0r4M1etaGHVdl0ES/afYZFzSiF3kwKx/qUc=; b=rq32CuBk5X2+Xev+zFjtWbTbukjVYgp052VQoUtKNOTE4Cda9Cy4Byz7X7TyDaf3TQ2I 6Xq6h/PXDcwuH55t84HlJx++IE29KeYzxGnud9iAcqceAw++4jace2g3nP5q9+tVQuDP JKmeME1MBZxG+r3eijrKz+I+/dFivoWQvUM6OVeVIggnFDVOUMogq4PMOpJhjY4t+4Ty T/Rv6uXJl+x2rhUlCA5dHNltlK7OXjBzMdts964clZe9v6/2TNndXTWUZGdIWr0yX2HO Q8vLkyWbeiF65glX8gZob//mF1Popwb6C6Z2TLKwVkfbusnbRd8Lf2e8RxtLEG/+nZ1T cg== Received: from userv0021.oracle.com (userv0021.oracle.com [156.151.31.71]) by userp2120.oracle.com with ESMTP id 2qhree55ng-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 14 Feb 2019 00:02:27 +0000 Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by userv0021.oracle.com (8.14.4/8.14.4) with ESMTP id x1E02QQh001435 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 14 Feb 2019 00:02:26 GMT Received: from abhmp0003.oracle.com (abhmp0003.oracle.com [141.146.116.9]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x1E02OhA014525; Thu, 14 Feb 2019 00:02:25 GMT Received: from concerto.internal (/24.9.64.241) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Wed, 13 Feb 2019 16:02:24 -0800 From: Khalid Aziz To: juergh@gmail.com, tycho@tycho.ws, jsteckli@amazon.de, ak@linux.intel.com, torvalds@linux-foundation.org, liran.alon@oracle.com, keescook@google.com, akpm@linux-foundation.org, mhocko@suse.com, catalin.marinas@arm.com, will.deacon@arm.com, jmorris@namei.org, konrad.wilk@oracle.com Cc: deepa.srinivasan@oracle.com, chris.hyser@oracle.com, tyhicks@canonical.com, dwmw@amazon.co.uk, andrew.cooper3@citrix.com, jcm@redhat.com, boris.ostrovsky@oracle.com, kanth.ghatraju@oracle.com, oao.m.martins@oracle.com, jmattson@google.com, pradeep.vincent@oracle.com, john.haxby@oracle.com, tglx@linutronix.de, kirill.shutemov@linux.intel.com, hch@lst.de, steven.sistare@oracle.com, labbott@redhat.com, luto@kernel.org, dave.hansen@intel.com, peterz@infradead.org, kernel-hardening@lists.openwall.com, linux-mm@kvack.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Khalid Aziz , "Vasileios P . Kemerlis" , Juerg Haefliger , Tycho Andersen , Marco Benatto , David Woodhouse Subject: [RFC PATCH v8 12/14] xpfo, mm: optimize spinlock usage in xpfo_kunmap Date: Wed, 13 Feb 2019 17:01:35 -0700 Message-Id: X-Mailer: git-send-email 2.17.1 In-Reply-To: References: In-Reply-To: References: X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9166 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1902130157 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Julian Stecklina Only the xpfo_kunmap call that needs to actually unmap the page needs to be serialized. We need to be careful to handle the case, where after the atomic decrement of the mapcount, a xpfo_kmap increased the mapcount again. In this case, we can safely skip modifying the page table. Model-checked with up to 4 concurrent callers with Spin. Signed-off-by: Julian Stecklina Signed-off-by: Khalid Aziz Cc: x86@kernel.org Cc: kernel-hardening@lists.openwall.com Cc: Vasileios P. Kemerlis Cc: Juerg Haefliger Cc: Tycho Andersen Cc: Marco Benatto Cc: David Woodhouse --- mm/xpfo.c | 25 ++++++++++++++++--------- 1 file changed, 16 insertions(+), 9 deletions(-) diff --git a/mm/xpfo.c b/mm/xpfo.c index dc03c423c52f..5157cbebce4b 100644 --- a/mm/xpfo.c +++ b/mm/xpfo.c @@ -124,28 +124,35 @@ EXPORT_SYMBOL(xpfo_kmap); void xpfo_kunmap(void *kaddr, struct page *page) { + bool flush_tlb = false; + if (!static_branch_unlikely(&xpfo_inited)) return; if (!PageXpfoUser(page)) return; - spin_lock(&page->xpfo_lock); - /* * The page is to be allocated back to user space, so unmap it from the * kernel, flush the TLB and tag it as a user page. */ if (atomic_dec_return(&page->xpfo_mapcount) == 0) { -#ifdef CONFIG_XPFO_DEBUG - BUG_ON(PageXpfoUnmapped(page)); -#endif - SetPageXpfoUnmapped(page); - set_kpte(kaddr, page, __pgprot(0)); - xpfo_flush_kernel_tlb(page, 0); + spin_lock(&page->xpfo_lock); + + /* + * In the case, where we raced with kmap after the + * atomic_dec_return, we must not nuke the mapping. + */ + if (atomic_read(&page->xpfo_mapcount) == 0) { + SetPageXpfoUnmapped(page); + set_kpte(kaddr, page, __pgprot(0)); + flush_tlb = true; + } + spin_unlock(&page->xpfo_lock); } - spin_unlock(&page->xpfo_lock); + if (flush_tlb) + xpfo_flush_kernel_tlb(page, 0); } EXPORT_SYMBOL(xpfo_kunmap); -- 2.17.1