From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752688AbbARRNW (ORCPT ); Sun, 18 Jan 2015 12:13:22 -0500 Received: from smtp.codeaurora.org ([198.145.11.231]:51081 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751562AbbARRNV (ORCPT ); Sun, 18 Jan 2015 12:13:21 -0500 Date: Sun, 18 Jan 2015 22:43:16 +0530 From: Shiraz Hashim To: Naoya Horiguchi Cc: "linux-mm@kvack.org" , "akpm@linux-foundation.org" , "oleg@redhat.com" , "gorcunov@openvz.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 1/1] mm: pagemap: limit scan to virtual region being asked Message-ID: <20150118171315.GA25218@shashim-linux.in.qualcomm.com> References: <1421152024-6204-1-git-send-email-shashim@codeaurora.org> <20150114010830.GA16100@hori1.linux.bs1.fc.nec.co.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150114010830.GA16100@hori1.linux.bs1.fc.nec.co.jp> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 14, 2015 at 01:08:40AM +0000, Naoya Horiguchi wrote: > On Tue, Jan 13, 2015 at 05:57:04PM +0530, Shiraz Hashim wrote: > > pagemap_read scans through the virtual address space of a > > task till it prepares 'count' pagemaps or it reaches end > > of task. > > > > This presents a problem when the page walk doesn't happen > > for vma with VM_PFNMAP set. In which case walk is silently > > skipped and no pagemap is prepare, in turn making > > pagemap_read to scan through task end, even crossing beyond > > 'count', landing into a different vma region. This leads to > > wrong presentation of mappings for that vma. > > > > Fix this by limiting end_vaddr to the end of the virtual > > address region being scanned. > > > > Signed-off-by: Shiraz Hashim > > This patch works in some case, but there still seems a problem in > another case. > > Consider that we have two vmas within some narrow > (PAGEMAP_WALK_SIZE) region. One vma in lower address is VM_PFNMAP, > and the other vma in higher address is not. Then a single call of > walk_page_range() skips the first vma and scans the second vma, but > the pagemap record of the second vma will be stored on the wrong > offset in the buffer, because we just skip vma(VM_PFNMAP) without > calling any callbacks (within which add_to_pagemap() increments > pm.pos). > > So calling pte_hole() for vma(VM_PFNMAP) looks a better fix to me. > Thanks. That makes sense, If you are okay, I can send following patch formally. diff --git a/mm/pagewalk.c b/mm/pagewalk.c index ad83195..b16ea60 100644 --- a/mm/pagewalk.c +++ b/mm/pagewalk.c @@ -200,6 +200,11 @@ int walk_page_range(unsigned long addr, unsigned long end, if ((vma->vm_start <= addr) && (vma->vm_flags & VM_PFNMAP)) { next = vma->vm_end; + if (walk->pte_hole) + err = walk->pte_hole(addr, next, walk); + if (err) + break; + pgd = pgd_offset(walk->mm, next); continue; } regards Shiraz