Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
In-Reply-To: <20180425112415.12327-2-pagupta@redhat.com>
References: <20180425112415.12327-1-pagupta@redhat.com> <20180425112415.12327-2-pagupta@redhat.com>
From:   Dan Williams <dan.j.williams@intel.com>
Date:   Wed, 25 Apr 2018 07:21:21 -0700
Message-ID: <CAPcyv4hvrB08XPTbVK0xT2_1Xmaid=-v3OMxJVDTNwQucsOHLA@mail.gmail.com>
Subject: Re: [RFC v2 1/2] virtio: add pmem driver
To:     Pankaj Gupta <pagupta@redhat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        KVM list <kvm@vger.kernel.org>,
        Qemu Developers <qemu-devel@nongnu.org>,
        linux-nvdimm <linux-nvdimm@ml01.01.org>,
        Linux MM <linux-mm@kvack.org>, Jan Kara <jack@suse.cz>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        Rik van Riel <riel@surriel.com>,
        Haozhong Zhang <haozhong.zhang@intel.com>,
        Nitesh Narayan Lal <nilal@redhat.com>,
        Kevin Wolf <kwolf@redhat.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        "Zwisler, Ross" <ross.zwisler@intel.com>,
        David Hildenbrand <david@redhat.com>,
        Xiao Guangrong <xiaoguangrong.eric@gmail.com>,
        Christoph Hellwig <hch@infradead.org>,
        Marcel Apfelbaum <marcel@redhat.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        niteshnarayanlal@hotmail.com, Igor Mammedov <imammedo@redhat.com>,
        lcapitulino@redhat.com
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, Apr 25, 2018 at 4:24 AM, Pankaj Gupta <pagupta@redhat.com> wrote:
> This patch adds virtio-pmem driver for KVM
> guest.

Minor nit, please expand your changelog line wrapping to 72 columns.

>
> 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.

We need some additional enabling to disable MAP_SYNC for this
configuration. In other words, if fsync() is required then we must
disable the MAP_SYNC optimization. I think this should be a struct
dax_device property looked up at mmap time in each MAP_SYNC capable
->mmap() file operation implementation.