[Xen-devel] Xen, EFI and kexec

[Sylvain Munaut <s.munaut@xxxxxxxxxxxxxxxxxxxx>]

Hi,


A bit of background: What I'm currently trying to do is to network
boot a first linux image in EFI mode (using UEFI network boot), then
from that image, kexec into Xen in EFI mode as well.

It's not working.

When you kexec into another linux in EFI mode, kexec actually passes
some more infos to the kernel to allow it to use EFI mode properly.
IIUC Linux also maps the various EFI ranges at deterministic addresses
because the seting up EFI virtual address mode is only allowed once
per boot and so both the old and new kernel have to use the same
mappings.

I have seen the patch series by Daniel Kiper to add support for
multiboot2 protocol and EFI support for it. This seems like a good
step toward what I'd like to do. Adding multiboot2 support to kexec
user tools seems like something I could do. This should allow Xen to
get the info it needs.

However I don't think that'll be sufficient.

By the time kexec will launch Xen, the first kernel will have done an
"ExitBootServices". And looking at Daniel's patch, that seems to be an
issue.

I'm also not sure if the EFI virtual address mode will be an issue or
not yet. (i.e. Xen uses the physical address mode, but is that usable
after the first linux setup the virtual mode).

Is there anything else I overlooked that will be an issue ?

Is this a use case worth supporting ? (Obviously I think so, but I'm biased :p)

And if I'm looking at it the wrong way, what way should I be looking at it ?


Cheers,

    Sylvain Munaut


PS: I'm currently making my way through the 2000+ pages of the EFI
specs so I probably got some things wrong above ...

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