Re: [Xen-devel] [PATCH 4/4] hvmloader: add support to load extra ACPI tables from qemu

[Haozhong Zhang <haozhong.zhang@xxxxxxxxx>]

On 01/20/16 10:41, Konrad Rzeszutek Wilk wrote:
> > > > > 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?
>

Interesting and good to know this. I'll have a look at it.

Thanks,
Haozhong

> > 
> > 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?
> 
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