From mboxrd@z Thu Jan  1 00:00:00 1970
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: [PATCH 4/4] hvmloader: add support to load extra
 ACPI tables from qemu
Date: Wed, 20 Jan 2016 10:41:06 -0500
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> > > > Neither of these are sufficient however.  That gets Qemu a mapping of
> > > > the NVDIMM, not the guest.  Something, one way or another, has to turn
> > > > this into appropriate add-to-phymap hypercalls.
> > > >
> > > 
> > > Yes, those hypercalls are what I'm going to add.
> > 
> > Why?
> > 
> > What you need (in a rought hand-wave way) is to:
> >  - mount /dev/pmem0
> >  - mmap the file on /dev/pmem0 FS
> >  - walk the VMA for the file - extract the MFN (machien frame numbers)
> 
> Can this step be done by QEMU? Or does linux kernel provide some
> approach for the userspace to do the translation?

I don't know. I would think no - as you wouldn't want the userspace
application to figure out the physical frames from the virtual
address (unless they are root). But then if you look in
/proc/<pid>/maps and /proc/<pid>/smaps there are some data there.

Hm, /proc/<pid>/pagemaps has something intersting

See pagemap_read function. That looks to be doing it?

> 
> Haozhong
> 
> >  - feed those frame numbers to xc_memory_mapping hypercall. The
> >    guest pfns would be contingous.
> >    Example: say the E820_NVDIMM starts at 8GB->16GB, so an 8GB file on
> >    /dev/pmem0 FS - the guest pfns are 0x200000 upward.
> > 
> >    However the MFNs may be discontingous as the NVDIMM could be an
> >    1TB - and the 8GB file is scattered all over.
> > 
> > I believe that is all you would need to do?