Re: [Xen-devel] [XEN-devel] arm64: fix incorrect pa_range_info table to support 42 bit PA systems.

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 15/05/17 18:11, Feng Kan wrote:
> On Mon, May 15, 2017 at 7:53 AM, Julien Grall <julien.grall@xxxxxxx> wrote:
> > Hello Feng,
> >
> > On 13/05/17 01:26, Feng Kan wrote:
> > > The pa_range_info table contain incorrect root_order and t0sz which
> > > prevent 42 bit PA systems from booting dom0.
> >
> > As I mentioned in the previous thread [1], this is not a bug. What you
> > configure below is the stage-2 page table and not the hypervisor page-table.
> >
> > It is perfectly fine to expose less IPA (Intermediate Physical Address) bits
> > than the number of PA (Physical Address) bits as long as all the address
> > wired are below 40 bits (assumption made by the patch who added this code).
> > Does your hardware have devices/RAM above 40 bits?
> Yes,  the APM X-Gene series have all been 42 bit PA systems.
> Particularly X-Gene 3, which
> has its PCIe0 all the way up starting at 41 bit.
Thank you for the information.

> If so, then you need to
> > mention in the commit message.
> I will be more clear in the commit message.
> > This bring another question, now you will allocate 8 pages by default for
> > both DOM0 and guests. Exposing 42 bits IPA to a guest does not sound
> > necessary, so we would waste memory here. How are you going to address that?
> To be honest, I hadn't thought of that. I had assume system such as
> these would have
> plenty of memory. I will take a look regarding this. If you have any
> suggestions that would
> be greatly appreciated
I am not totally against using 8 pages. Although a TODO will be useful 
in the code and the commit message.
Cheers,

--
Julien Grall

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