From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) by kanga.kvack.org (Postfix) with ESMTP id DBC3B6B0003 for ; Tue, 2 Oct 2018 06:05:33 -0400 (EDT) Received: by mail-ed1-f69.google.com with SMTP id g36-v6so983824edb.3 for ; Tue, 02 Oct 2018 03:05:33 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id l12-v6si577192edj.314.2018.10.02.03.05.32 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 02 Oct 2018 03:05:32 -0700 (PDT) Date: Tue, 2 Oct 2018 12:05:31 +0200 From: Jan Kara Subject: Problems with VM_MIXEDMAP removal from /proc//smaps Message-ID: <20181002100531.GC4135@quack2.suse.cz> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="YZ5djTAD1cGYuMQK" Content-Disposition: inline Sender: owner-linux-mm@kvack.org List-ID: To: Dan Williams , Dave Jiang Cc: linux-nvdimm@lists.01.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, jthumshirn@suse.de --YZ5djTAD1cGYuMQK Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Hello, commit e1fb4a086495 "dax: remove VM_MIXEDMAP for fsdax and device dax" has removed VM_MIXEDMAP flag from DAX VMAs. Now our testing shows that in the mean time certain customer of ours started poking into /proc//smaps and looks at VMA flags there and if VM_MIXEDMAP is missing among the VMA flags, the application just fails to start complaining that DAX support is missing in the kernel. The question now is how do we go about this? Strictly speaking, this is a userspace visible regression (as much as I think that application poking into VMA flags at this level is just too bold). Is there any precedens in handling similar issues with smaps which really exposes a lot of information that is dependent on kernel implementation details? I have attached a patch that is an obvious "fix" for the issue - just fake VM_MIXEDMAP flag in smaps. But I'm open to other suggestions... Honza -- Jan Kara SUSE Labs, CR --YZ5djTAD1cGYuMQK Content-Type: text/x-patch; charset=us-ascii Content-Disposition: attachment; filename="0001-proc-Show-DAX-mappings-as-having-VM_MIXEDMAP-flag.patch" --YZ5djTAD1cGYuMQK--