From patchwork Thu Nov 19 00:36:24 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ross Zwisler X-Patchwork-Id: 546255 Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id B6BE4141497 for ; Thu, 19 Nov 2015 11:37:43 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932297AbbKSAg1 (ORCPT ); Wed, 18 Nov 2015 19:36:27 -0500 Received: from mga14.intel.com ([192.55.52.115]:31912 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757338AbbKSAgZ (ORCPT ); Wed, 18 Nov 2015 19:36:25 -0500 Received: from orsmga002.jf.intel.com ([10.7.209.21]) by fmsmga103.fm.intel.com with ESMTP; 18 Nov 2015 16:36:25 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.20,315,1444719600"; d="scan'208";a="854133134" Received: from theros.lm.intel.com (HELO linux.intel.com) ([10.232.112.87]) by orsmga002.jf.intel.com with ESMTP; 18 Nov 2015 16:36:24 -0800 Date: Wed, 18 Nov 2015 17:36:24 -0700 From: Ross Zwisler To: Toshi Kani Cc: Dan Williams , Ross Zwisler , linux-nvdimm , Ross Zwisler , linux-fsdevel , linux-ext4 Subject: Re: dax pmd fault handler never returns to userspace Message-ID: <20151119003624.GA26287@linux.intel.com> Mail-Followup-To: Ross Zwisler , Toshi Kani , Dan Williams , linux-nvdimm , Ross Zwisler , linux-fsdevel , linux-ext4 References: <20151118170014.GB10656@linux.intel.com> <20151118182320.GA7901@linux.intel.com> <1447882389.21443.151.camel@hpe.com> <1447884281.21443.154.camel@hpe.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <1447884281.21443.154.camel@hpe.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Wed, Nov 18, 2015 at 03:04:41PM -0700, Toshi Kani wrote: > On Wed, 2015-11-18 at 13:57 -0800, Dan Williams wrote: > > On Wed, Nov 18, 2015 at 1:33 PM, Toshi Kani wrote: > > > I am seeing a similar/same problem in my test. I think the problem is that > > > in > > > case of a WP fault, wp_huge_pmd() -> __dax_pmd_fault() -> > > > vmf_insert_pfn_pmd(), > > > which is a no-op since the PMD is mapped already. We need WP handling for > > > this > > > PMD map. > > > > > > If it helps, I have attached change for follow_trans_huge_pmd(). I have not > > > tested much, though. > > > > Interesting, I didn't get this far because my tests were crashing the > > kernel. I'll add this case the pmd fault test in ndctl. > > I hit this one with mmap(MAP_POPULATE). With this change, I then hit the WP > fault loop when writing to the range. Here's a fix - please let me know if this seems incomplete or incorrect for some reason. -- >8 -- From 02aa9f37d7ec9c0c38413f7e304b2577eb9f974a Mon Sep 17 00:00:00 2001 From: Ross Zwisler Date: Wed, 18 Nov 2015 17:15:09 -0700 Subject: [PATCH] mm: Allow DAX PMD mappings to become writeable Prior to this change DAX PMD mappings that were made read-only were never able to be made writable again. This is because the code in insert_pfn_pmd() that calls pmd_mkdirty() and pmd_mkwrite() would skip these calls if the PMD already existed in the page table. Instead, if we are doing a write always mark the PMD entry as dirty and writeable. Without this code we can get into a condition where we mark the PMD as read-only, and then on a subsequent write fault we get into an infinite loop of PMD faults where we try unsuccessfully to make the PMD writeable. Signed-off-by: Ross Zwisler --- mm/huge_memory.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index bbac913..1b3df56 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -877,15 +877,13 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, spinlock_t *ptl; ptl = pmd_lock(mm, pmd); - if (pmd_none(*pmd)) { - entry = pmd_mkhuge(pfn_pmd(pfn, prot)); - if (write) { - entry = pmd_mkyoung(pmd_mkdirty(entry)); - entry = maybe_pmd_mkwrite(entry, vma); - } - set_pmd_at(mm, addr, pmd, entry); - update_mmu_cache_pmd(vma, addr, pmd); + entry = pmd_mkhuge(pfn_pmd(pfn, prot)); + if (write) { + entry = pmd_mkyoung(pmd_mkdirty(entry)); + entry = maybe_pmd_mkwrite(entry, vma); } + set_pmd_at(mm, addr, pmd, entry); + update_mmu_cache_pmd(vma, addr, pmd); spin_unlock(ptl); }