Re: [Xen-devel] [PATCH] x86/boot: fix MB2 header to require EFI BS

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Tue, Oct 24, 2017 at 03:28:52PM -0500, Doug Goldstein wrote:
> On 10/24/17 3:08 PM, Daniel Kiper wrote:
> > On Tue, Oct 24, 2017 at 02:40:41PM -0500, Doug Goldstein wrote:
> >> The EFI multiboot2 entry point currently requires EFI BootServices to
> >> not have been exited however the header currently tells the boot
> >> loader that Xen optionally supports EFI BootServices having been exited.
> >> With this change Xen properly advertises that EFI must not be exited
> >> allowing the boot loader to report an error that it cannot boot Xen if
> >> it is unable to meet its needs.
> >>
> >> Signed-off-by: Doug Goldstein <cardoe@xxxxxxxxxx>
> >> ---
> >>
> >> This should likely be applied against Xen 4.9 and Xen 4.10 as well as
> >> staging. I am trying to get multiboot2 support for iPXE and upstream
> >> is concerned that leaving EFI BootServices enabled will not be
> >> compatible with their aims to support Secure Boot. So when I build
> >
> > Hmmm... What are exact arguments for that? How do they implement e.g.
> > chain loading then? What about the shim support?
>
> Look they have concerns about it. As we've talked about this in the past

If I do something I like to know why I have to do it.

> and I encourage you communicate with them. You are the author of the

I remember but, sorry, IIRC, I heard just only vague statements like that.
So, I would like to know exact reasons finally. And I hoped that they told
you more then simple "NO".

> multiboot2 spec. I'm just trying to do my best to PXE boot Xen on EFI
> systems and make all upstreams (Xen & iPXE) happy.

Once again, I am happy to help. Though I have to know why I have to do
this or that. No more no less.

> >> Unfortunately the spec is a bit vague and how I am reading it is:
> >> - no tag = exit boot services in the boot loader
> >> - tag present marked optional = boot loader can or cannot exit boot 
> >> services
> >> - tag present marked required = boot loader cannot exit boot services
> >
> > NACK, please take a look at section 3.1.4, Multiboot2 information request
> > in Multiboot2 spec. OPTIONAL/REQUIRED has different meaning for the 
> > bootloader
> > than you think.
>
> I still don't see any issue with my interpretation based on what you
> pointed me to. There's a hole here with what Xen asks for of the boot
> loader to do.
>
> The boot loader is told that Xen optionally supports the boot loader not
> exiting boot services when in fact Xen requires the boot loader to not
> exit boot services. Somehow we need to convey this to the boot loader.

Sorry, maybe I was too vague this time. Please look at my replay to Andrew.
It should help.

Daniel

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