Re: [Xen-devel] Xen, EFI and kexec

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Wed, Nov 09, 2016 at 11:24:44AM -0500, Konrad Rzeszutek Wilk wrote:
> On Wed, Nov 09, 2016 at 03:13:16PM +0100, Sylvain Munaut wrote:
> > 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
>
> CC-ing Daniel.
> > issue.

Looks interesting. I thought about that a bit but not much, so, just
hand waving. I have a feeling that in that situation we should skip
whole code in Xen which refers to EFI boot services. We just need to
pass essential info (taken during first boot) to Xen. Probably we can
use some of multiboot2 existing features. However, I have a feeling
that we need also some extensions that would enable us to say that
Xen boots on EFI platform but without access to boot services (kexecing).
This should not be very big issue. If you wish to work on this I am
able to review some design and patches for kexec, multiboot2 and GRUB
if needed. Just CC me.

Daniel

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