Re: [Xen-devel] pvgrub2 for ARM

[Ian Campbell]

On Wed, 2013-11-06 at 15:04 +0100, Vladimir 'φ-coder/phcoder' Serbinenko
wrote:
> On 06.11.2013 14:25, Ian Campbell wrote:
> > On Wed, 2013-11-06 at 14:00 +0100, Vladimir 'φ-coder/phcoder' Serbinenko
> > wrote:
> >> Hello, all. I've ported grub2 to x86_64-xen and i386-xen (PAE only). How
> >> big is the difference between ARM and i386 when seen as pv guest?
> > 
> > Very. Xen on ARM uses hardware functionality for second stage paging, so
> > there is far less porting to do.
> > 
> Well doesn't matter much for GRUB as we change paging only at init,
> before handoff and to init vfb.

Right, I would expect this to all be mostly the same as native ARM even
when running under Xen.

>  What about drivers?

They are the usual Xen PV drivers. There's some additional setup to
enable event channels etc which you won't have seen on PV x86, but it's
very similar to the PVHVM stuff stuff on x86.

> >> What's with 64-bit ARM?
> > 
> > TBH I thought the GRuB On ARM stuff was mainly targeting 64-bit (at
> > least within Linaro). Do you have native grub on 32-bit ARM already
> > then?
> > 
> GRUB on 32-bit ARM works. We have currently 2 ports:
> arm-uboot:
> I've tested it myself on Raspberry pi with U-boot and in qemu (not sure
> which machine right now, I think vexpress) with u-boot
> arm-efi:
> Apparently works but have never been able to test it myself.

Interesting, thanks.

> > As far as 64-bit hardware goes you will have a struggle finding any at
> > all right now, nevermind for under $100.
> > 
> > We should at some point be able to support the freely (as in beer)
> > available Foundation model, but we don't right now.
> > 
> >> Alternatively, I'll probably go for Google HP chromebook 11.
> > 
> > I don;t know about this one, but previous chromebooks have proved a pain
> > to get Xen onto, too hard to debug anything on them...
> > 
> You need to solder couple of pins and connect them to raspberry pi. Or
> get debug board.

Sounds much easier than the existing chromebooks then.

> >> Or may I have access to some server where I'd be able to run VMs with my
> >> kernel (GRUB) and HDD?
> > 
> > I'm afraid we don't here at least.
> > 
> Pity, sth like this would aid OS porters greatly.

This might be something which we can resolve once ARM stuff with virt
extensions becomes more prevalent and easy to get hold of. Although
perhaps by then the issue won't be so critical.

Ian.