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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 52A64C31E45 for ; Thu, 13 Jun 2019 21:37:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 31E71208CA for ; Thu, 13 Jun 2019 21:37:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727483AbfFMVh4 (ORCPT ); Thu, 13 Jun 2019 17:37:56 -0400 Received: from mga07.intel.com ([134.134.136.100]:44112 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726806AbfFMVhz (ORCPT ); Thu, 13 Jun 2019 17:37:55 -0400 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga105.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 13 Jun 2019 14:37:55 -0700 X-ExtLoop1: 1 Received: from iweiny-desk2.sc.intel.com ([10.3.52.157]) by orsmga008.jf.intel.com with ESMTP; 13 Jun 2019 14:37:54 -0700 Date: Thu, 13 Jun 2019 14:39:16 -0700 From: Ira Weiny To: Pingfan Liu Cc: linux-mm@kvack.org, Andrew Morton , Mike Rapoport , Dan Williams , Matthew Wilcox , John Hubbard , "Aneesh Kumar K.V" , Keith Busch , Christoph Hellwig , Shuah Khan , linux-kernel@vger.kernel.org Subject: Re: [PATCHv4 2/3] mm/gup: fix omission of check on FOLL_LONGTERM in gup fast path Message-ID: <20190613213915.GE32404@iweiny-DESK2.sc.intel.com> References: <1560422702-11403-1-git-send-email-kernelfans@gmail.com> <1560422702-11403-3-git-send-email-kernelfans@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1560422702-11403-3-git-send-email-kernelfans@gmail.com> User-Agent: Mutt/1.11.1 (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 13, 2019 at 06:45:01PM +0800, Pingfan Liu wrote: > FOLL_LONGTERM suggests a pin which is going to be given to hardware and > can't move. It would truncate CMA permanently and should be excluded. > > FOLL_LONGTERM has already been checked in the slow path, but not checked in > the fast path, which means a possible leak of CMA page to longterm pinned > requirement through this crack. > > Place a check in gup_pte_range() in the fast path. > > Signed-off-by: Pingfan Liu > Cc: Ira Weiny > Cc: Andrew Morton > Cc: Mike Rapoport > Cc: Dan Williams > Cc: Matthew Wilcox > Cc: John Hubbard > Cc: "Aneesh Kumar K.V" > Cc: Keith Busch > Cc: Christoph Hellwig > Cc: Shuah Khan > Cc: linux-kernel@vger.kernel.org > --- > mm/gup.c | 26 ++++++++++++++++++++++++++ > 1 file changed, 26 insertions(+) > > diff --git a/mm/gup.c b/mm/gup.c > index 766ae54..de1b03f 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -1757,6 +1757,14 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, > VM_BUG_ON(!pfn_valid(pte_pfn(pte))); > page = pte_page(pte); > > + /* > + * FOLL_LONGTERM suggests a pin given to hardware. Prevent it > + * from truncating CMA area > + */ > + if (unlikely(flags & FOLL_LONGTERM) && > + is_migrate_cma_page(page)) > + goto pte_unmap; > + > head = try_get_compound_head(page, 1); > if (!head) > goto pte_unmap; > @@ -1900,6 +1908,12 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, > refs++; > } while (addr += PAGE_SIZE, addr != end); > > + if (unlikely(flags & FOLL_LONGTERM) && > + is_migrate_cma_page(page)) { > + *nr -= refs; > + return 0; > + } > + Why can't we place this check before the while loop and skip subtracting the page count? Can is_migrate_cma_page() operate on any "subpage" of a compound page? Here this calls is_magrate_cma_page() on the tail page of the compound page. I'm not an expert on compound pages nor cma handling so is this ok? It seems like you need to call is_migrate_cma_page() on each page within the while loop? > head = try_get_compound_head(pmd_page(orig), refs); > if (!head) { > *nr -= refs; > @@ -1941,6 +1955,12 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, > refs++; > } while (addr += PAGE_SIZE, addr != end); > > + if (unlikely(flags & FOLL_LONGTERM) && > + is_migrate_cma_page(page)) { > + *nr -= refs; > + return 0; > + } > + Same comment here. > head = try_get_compound_head(pud_page(orig), refs); > if (!head) { > *nr -= refs; > @@ -1978,6 +1998,12 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr, > refs++; > } while (addr += PAGE_SIZE, addr != end); > > + if (unlikely(flags & FOLL_LONGTERM) && > + is_migrate_cma_page(page)) { > + *nr -= refs; > + return 0; > + } > + And here. Ira > head = try_get_compound_head(pgd_page(orig), refs); > if (!head) { > *nr -= refs; > -- > 2.7.5 >