From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dan Williams <dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Subject: Re: [PATCH v2 2/2] virtio-pmem: Add virtio pmem driver
Date: Sat, 13 Oct 2018 09:10:13 -0700
Message-ID: <CAPcyv4hroaVWA-HgjWCnr7QTd_y7U8sCvS+Up733ttnD6_cKzQ@mail.gmail.com>
References: <20181013050021.11962-1-pagupta@redhat.com>
 <20181013050021.11962-3-pagupta@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org>
In-Reply-To: <20181013050021.11962-3-pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
List-Unsubscribe: <https://lists.01.org/mailman/options/linux-nvdimm>,
 <mailto:linux-nvdimm-request-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org?subject=unsubscribe>
List-Archive: <http://lists.01.org/pipermail/linux-nvdimm/>
List-Post: <mailto:linux-nvdimm-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org>
List-Help: <mailto:linux-nvdimm-request-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org?subject=help>
List-Subscribe: <https://lists.01.org/mailman/listinfo/linux-nvdimm>,
 <mailto:linux-nvdimm-request-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org?subject=subscribe>
Errors-To: linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org
Sender: "Linux-nvdimm" <linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org>
To: Pankaj Gupta <pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: Kevin Wolf <kwolf-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>, Xiao Guangrong <xiaoguangrong.eric-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, KVM list <kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Rik van Riel <riel-ebMLmSuQjDVBDgjK7y7TUQ@public.gmane.org>, linux-nvdimm <linux-nvdimm-y27Ovi1pjclAfugRpC6u6w@public.gmane.org>, David Hildenbrand <david-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Linux Kernel Mailing List <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Qemu Developers <qemu-devel-qX2TKyscuCcdnm+yROfE0A@public.gmane.org>, Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, Igor Mammedov <imammedo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, "Michael S. Tsirkin" <mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Stefan Hajnoczi <stefanha-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, zwisler-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, lcapitulino-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, Paolo Bonzini <pbonzini-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Nitesh Narayan Lal <nilal-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Eric Blake <eblake-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
List-Id: linux-nvdimm@lists.01.org

On Fri, Oct 12, 2018 at 10:01 PM Pankaj Gupta <pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
>
> This patch adds virtio-pmem driver for KVM guest.
>
> Guest reads the persistent memory range information from
> Qemu over VIRTIO and registers it on nvdimm_bus. It also
> creates a nd_region object with the persistent memory
> range information so that existing 'nvdimm/pmem' driver
> can reserve this into system memory map. This way
> 'virtio-pmem' driver uses existing functionality of pmem
> driver to register persistent memory compatible for DAX
> capable filesystems.
>
> This also provides function to perform guest flush over
> VIRTIO from 'pmem' driver when userspace performs flush
> on DAX memory range.

Before we can move forward with this driver we need additional
filesystem enabling to detect when the backing device is fronting DAX
pmem or a paravirtualized page cache through virtio-pmem. Any
interface that requires fsync() and a round trip to the hypervisor to
flush host page cache is not DAX.