Re: Xen DomU Bootloader Experiences

[Elliott Mitchell <ehem+xen@xxxxxxx>]

On Thu, Nov 13, 2025 at 10:13:07PM +0200, Grygorii Strashko wrote:
> 
> On 12.11.25 23:13, Elliott Mitchell wrote:
> > 
> > Recommendations:
> > PyGRUB is functional within its limits.  Problems are GRUBv1 syntax and
> > running within Domain 0.  Given this I feel the Xen Project should be
> > heading towards deprecating PyGRUB.  Since PvGRUB works for x86 now, I
> > would default to neither building nor installing PyGRUB on x86.  For
> > other architectures PyGRUB is still useful.
> > 
> > The Xen Project should formally ask the GRUB Project to port PvGRUB to
> > ARM, RISC-V and PowerPC.  The need for PvGRUB on ARM seems rather urgent.
> > Without a proper bootloader VMs aren't too useful.
> > 
> > 
> > The Xen Project needs people to work with EDK2/Tianocore.  The oldest
> > report I've seen of the EDK2/Tianocore issue dates to mid-2023.  Now two
> > years later the bug is still present.
> > 
> > The ability to configure XEN_EFI.fd as a domain kernel is a feature
> > highly worthy of being ported to x86.  For OSes which don't particularly
> > like GRUB, but do have PV drivers this is an ideal boot method.
> 
> Just curious, you did not mention u-boot which is widely used on ARM,
> for example Android guests boot using it.

As I have not used U-Boot to load a DomU I did not write about something
I have not done.  Have you used U-Boot to load a DomU?  Was it a pleasant
experience?  Was it easy to setup?  Was it difficult to setup?

PyGRUB still has a bit of value since it can still load some Linux
guests.  GRUBv1 syntax is a major weakness, so I think the Xen Project
should be heading towards deprecating PyGRUB.  Mostly this needs GRUB's
Xen support to be ported to ARM and RISC-V.

GRUB's Xen support works great for x86.  Pleasant experience with minimal
trouble.  This is great for loading Linux in a DomU.

Tianocore/EDK2 support worked (past tense) great for ARM64.  Pleasant
experience with minimal trouble.  I haven't done full installation, but I
expect full installation will be a breeze (sigh getting patches into some
projects is extremely difficult).



Grygorii Strashko, do you think U-Boot is likely to cover some scenario
not covered by either GRUB or Tianocore/EDK2?  Do you think U-Boot is
likely to do a better job with some scenario than either GRUB or
Tianocore/EDK2?

You mentioned using U-Boot to load Android DomUs on ARM.  Is that likely
to be difficult to switch to Tianocore/EDK2?


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