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Re: [Xen-devel] booting Xen from EFI

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Subject: Re: [Xen-devel] booting Xen from EFI
From: Chris Dalton <cid@xxxxxx>
Date: Fri, 17 Jun 2011 17:15:48 +0100
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On 15/06/11 13:48, Jan Beulich wrote:
> While supposedly (or just theoretically?) it is possible to boot Xen
> indirectly through e.g. GrUB2's EFI support, any use of an
> intermediate boot loader is bogus when using EFI - Linux has to do
> so because of its custom load file format, but Xen certainly doesn't
> have to follow this (as it also uses the more generic multiboot
> protocol when booted from GrUB).

Interesting. I can boot Xen under EFI but do use an external boot loader
(which can be grub). Boot log below from my Sandybridge based system.
This system has a development EFI bios (with no CSM available) and where
the location of things like the RSDP do need to be pulled from the EFI
system table.

The approach I took was to add an EFI signature and system table field
to the multiboot info structure. (Multiboot2 already has these fields
but it seems Xen only ever supported that for powerpc).

Also, I allowed Xen to pickup the framebuffer info which is already part
of the mbi used by the latest versions of grub2. With those mods I get
efi_gop and efi_uga display output. I also modified Xen to access
ACPI/SMBIOS tables, etc from the EFI system table pointer. For dom0 I
used a hypercall (called from xen_start_kernel) to get the EFI info from
Xen (System table address, etc) and poke that into the boot_params field
linux uses for EFI boot.

At the moment, I don't propagate the efi memmap and just keep the mbi
based one (that is why there is a ioremap warning from the linux boot log).

Anyway, a bit hacky and needs tidying up but it does boot ok. (The
warning about not entering efi virtual mode is a work around for a
particular problem with this development BIOS).


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