From mboxrd@z Thu Jan  1 00:00:00 1970
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: [RFC Design Doc] Add vNVDIMM support for Xen
Date: Wed, 3 Feb 2016 10:35:09 -0500
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To: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Juergen Gross <jgross@suse.com>, Haozhong Zhang <haozhong.zhang@intel.com>, Kevin Tian <kevin.tian@intel.com>, Keir Fraser <keir@xen.org>, Ian Campbell <ian.campbell@citrix.com>, George Dunlap <George.Dunlap@eu.citrix.com>, Andrew Cooper <andrew.cooper3@citrix.com>, Xiao Guangrong <guangrong.xiao@linux.intel.com>, Ian Jackson <ian.jackson@eu.citrix.com>, George Dunlap <george.dunlap@citrix.com>, xen-devel@lists.xen.org, Jan Beulich <jbeulich@suse.com>, Jun Nakajima <jun.nakajima@intel.com>, Wei Liu <wei.liu2@citrix.com>
List-Id: xen-devel@lists.xenproject.org

On Wed, Feb 03, 2016 at 03:22:59PM +0000, Stefano Stabellini wrote:
> On Wed, 3 Feb 2016, George Dunlap wrote:
> > On 03/02/16 12:02, Stefano Stabellini wrote:
> > > On Wed, 3 Feb 2016, Haozhong Zhang wrote:
> > >> Or, we can make a file system on /dev/pmem0, create files on it, set
> > >> the owner of those files to xen-qemuuser-domid$domid, and then pass
> > >> those files to QEMU. In this way, non-root QEMU should be able to
> > >> mmap those files.
> > > 
> > > Maybe that would work. Worth adding it to the design, I would like to
> > > read more details on it.
> > > 
> > > Also note that QEMU initially runs as root but drops privileges to
> > > xen-qemuuser-domid$domid before the guest is started. Initially QEMU
> > > *could* mmap /dev/pmem0 while is still running as root, but then it
> > > wouldn't work for any devices that need to be mmap'ed at run time
> > > (hotplug scenario).
> > 
> > This is basically the same problem we have for a bunch of other things,
> > right?  Having xl open a file and then pass it via qmp to qemu should
> > work in theory, right?
> 
> Is there one /dev/pmem? per assignable region? Otherwise it wouldn't be
> safe.

Can be - which may be interleaved on multiple NVDIMMs. But we would operate
on files (on the /dev/pmem which has an DAX enabled filesystem).