Re: [Xen-users] Running Xen on RaspberryPi-3-B

[André Przywara <andre.przywara@xxxxxxx>]

On 23/07/2019 19:09, Rajagopal Aravindan wrote:

Hi

> On Tue, Jul 23, 2019 at 1:57 AM Rajagopal Aravindan
> <a.rajagopal.81@xxxxxxxxx <mailto:a.rajagopal.81@xxxxxxxxx>> wrote:
> 
>     Hello Andre,
> 
>     On Sun 21 Jul, 2019, 5:45 AM André Przywara, <andre.przywara@xxxxxxx
>     <mailto:andre.przywara@xxxxxxx>> wrote:
> 
>         On 20/07/2019 17:39, Julien Grall wrote:
> 
>         Hi,
> 
>         > On 7/20/19 4:39 AM, Rajagopal Aravindan wrote:
>         >> Hello Julien,
>         >>
>         >> Appreciate your reply, thanks.
>         >>
>         >>  > Instead I would recommend to look at the new RPI4.
>         >> Sure, will give it a look-in.
>         >>
>         >>  >It contains a GIC and the port should be easier.
>         >> Does that mean Xen won't run straight away and some porting
>         needs to
>         >> be done ?
> 
>         Not much needed on the Xen side, I got away with a small patch
>         for the
>         UART. Using CONFIG_EARLY_PRINTK=8250,0xfe215040,2 should give
>         you some
>         output even without it:
>         https://pastebin.com/uZqQ2XPm
> 
>         You need to have some more decent firmware than what is shipped,
>         though.
> 
>         > I bought one recently but I haven't yet had the chance to see
>         how much
>         > effort is required to getting Xen running on it.
>         >
>         > For some general guidance on porting a new board to Xen,
>         please see [1].
>         >
>         >> Again, any directions would be helpful, on where/what to
>         start with.
>         >>
>         >>  > So porting Xen on the RPI 3 is probably going to be quite
>         consequent.
>         >> Sounds like Xen & its guests can be made to run on RPi3, assuming
>         >> information on BRCM GIC is available on the net.
>         >
>         > The RPI 3 does not use the GIC so I am not sure what you found
>         online...
>         >
>         >> If yes,
>         >>
>         >>   * Getting Xen to run on RPi3 would be a very good case
>         study for
>         >>     understanding its internals, for Xen beginner like me.
>         >
>         > I don't think trying to port Xen on the RPI 3 is a good way to
>         > understand the internals. It would be best to look at platform
>         that are
>         > closer to Xen requirements...
>         >
>         >>   * Should anyone manage to get it running on RPi3  ...
>         >>       o Would Xen be willing to take it upstream ?
>         >
>         > Not really. See below...
>         >
>         >>       o Or are there reservations about it, since it may NOT
>         be useful
>         >>         on other hardware and hence not worth maintaining ?
>         >
>         > AFAIK, the interrupt controller used by the RPI 3 does not support
>         > virtualization. So this is quite departure from the minimal
>         requirement
>         > used by Xen.
>         >
>         > There are various way to make it working on Xen:
>         >    1) Emulating the interrupt controller
>         >    2) Use a PV interface as used by x86
>         >
>         > In both cases, the work is going to be consequent with very
>         limited
>         > benefits to other platforms.
> 
>         I agree on this, adding support for the RPi3 interrupt
>         controller would
>         be quite painful, and also needs to be integrated with the existing
>         (V)GIC support, which has the potential to introduce regressions.
>         Plus you need to amend the arch timer code, as this is
>         integrated with
>         the GIC for virtualisation purposes.
>         AFAIK the RPi3 is one of the few (if not the only one) ARM64
>         platform
>         without a GIC, and given that the RPi4 fixes this, I don't see
>         much hope
>         for upstreaming this kind of change.
> 
>         If you are desperate for (hardware) virtualisation, KVM supports
>         guests
>         without a (hardware) GIC (via the QEMU emulation), although this is
>         slower and less tested. Or you just go for some container solution.
> 
>         Cheers,
>         Andre.
> 
> 
>     I built Xen with your CONFIG_EARLY_PRINTK but couldn't meet with
>     success.
> 
>     That brings me to your point about decent firmware. I am using
>     u-boot 2019. Is that good enough?
> 
>     Thanks,
>     Rajagopal
> 
> 
>  Could you also please share the fdt set /chosen for xen bootargs, for
> RPi-4, if u-boot 2019 is good enough ?

Not sure what you mean with "U-Boot 2019"? Can't find such thing, it's
v2019.07, at best. But AFAIK RPi4 support has been just seen on the
list, I don't see it merged in there.

So for the firmware I am just using some Trusted Firmware port I came up
with:
https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/1629

You would also need Stefano's series for dealing with reserved-memory,
otherwise Xen will overwrite ATF. Haven't tested this yet, though.

Cheers,
Andre.

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