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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 05D6AC433E0 for ; Wed, 24 Jun 2020 05:47:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DDC2020781 for ; Wed, 24 Jun 2020 05:47:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388823AbgFXFrM (ORCPT ); Wed, 24 Jun 2020 01:47:12 -0400 Received: from verein.lst.de ([213.95.11.211]:42776 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726133AbgFXFrL (ORCPT ); Wed, 24 Jun 2020 01:47:11 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 7C6FF68AEF; Wed, 24 Jun 2020 07:47:08 +0200 (CEST) Date: Wed, 24 Jun 2020 07:47:08 +0200 From: Christoph Hellwig To: Keith Busch Cc: Christoph Hellwig , Baolin Wang , axboe@fb.com, sagi@grimberg.me, baolin.wang7@gmail.com, linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/3] nvme-pci: Add controller memory buffer supported macro Message-ID: <20200624054708.GA17008@lst.de> References: <20200623162751.GA4846@lst.de> <20200624025817.GC1291930@dhcp-10-100-145-180.wdl.wdc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200624025817.GC1291930@dhcp-10-100-145-180.wdl.wdc.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 23, 2020 at 07:58:17PM -0700, Keith Busch wrote: > On Tue, Jun 23, 2020 at 06:27:51PM +0200, Christoph Hellwig wrote: > > On Tue, Jun 23, 2020 at 09:24:33PM +0800, Baolin Wang wrote: > > > Introduce a new capability macro to indicate if the controller > > > supports the memory buffer or not, instead of reading the > > > NVME_REG_CMBSZ register. > > > > This is a complex issue. The CMBS bit was only added in NVMe 1.4 as > > a backwards incompatible change, as the CMB addressing scheme can lead > > to data corruption. The CMBS was added as part of the horribe hack > > that also involves the CBA field, which we'll need to see before > > using it to work around the addressing issue. At the same time we > > should also continue supporting the legacy pre-1.4 CMB with a warning > > (and may reject it if we know we run in a VM). > > Well, a CMB from an emulated controller (like qemu's) can be used within > a VM. It's only if you direct assign a PCI function that CMB usage > breaks. But we have no idea if a controller is assigned or emulated.