From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ot0-f198.google.com (mail-ot0-f198.google.com [74.125.82.198]) by kanga.kvack.org (Postfix) with ESMTP id 541866B0010 for ; Mon, 7 May 2018 15:30:42 -0400 (EDT) Received: by mail-ot0-f198.google.com with SMTP id l3-v6so21509540otk.4 for ; Mon, 07 May 2018 12:30:42 -0700 (PDT) Received: from mail-sor-f41.google.com (mail-sor-f41.google.com. [209.85.220.41]) by mx.google.com with SMTPS id e80-v6sor10669376oic.44.2018.05.07.12.30.41 for (Google Transport Security); Mon, 07 May 2018 12:30:41 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20180507191857.GA15604@bombadil.infradead.org> References: <1525704627-30114-1-git-send-email-yehs1@lenovo.com> <20180507184622.GB12361@bombadil.infradead.org> <20180507191857.GA15604@bombadil.infradead.org> From: Dan Williams Date: Mon, 7 May 2018 12:30:40 -0700 Message-ID: Subject: Re: [RFC PATCH v1 0/6] use mm to manage NVDIMM (pmem) zone Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox Cc: Huaisheng Ye , Michal Hocko , Linux Kernel Mailing List , linux-nvdimm , Tetsuo Handa , chengnt@lenovo.com, pasha.tatashin@oracle.com, Sasha Levin , Linux MM , Johannes Weiner , Andrew Morton , colyli@suse.de, Mel Gorman , Vlastimil Babka , Dave Hansen On Mon, May 7, 2018 at 12:18 PM, Matthew Wilcox wrote: > On Mon, May 07, 2018 at 11:57:10AM -0700, Dan Williams wrote: >> I think adding yet one more mm-zone is the wrong direction. Instead, >> what we have been considering is a mechanism to allow a device-dax >> instance to be given back to the kernel as a distinct numa node >> managed by the VM. It seems it times to dust off those patches. > > I was wondering how "safe" we think that ability is. NV-DIMM pages > (obviously) differ from normal pages by their non-volatility. Do we > want their contents from the previous boot to be observable? If not, > then we need the BIOS to clear them at boot-up, which means we would > want no kernel changes at all; rather the BIOS should just describe > those pages as if they were DRAM (after zeroing them). Certainly the BIOS could do it, but the impetus for having a kernel mechanism to do the same is for supporting the configuration flexibility afforded by namespaces, or otherwise having the capability when the BIOS does not offer it. However, you are right that there are extra security implications when System-RAM is persisted, perhaps requiring the capacity to be explicitly locked / unlocked could address that concern?