linux-kernel - Re: [PATCH] efi/libstub/fdt: Standardize the names of EFI stub parameters

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Message-ID: <20150910162302.GN29293@leverpostej>
Date:	Thu, 10 Sep 2015 17:23:02 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	Shannon Zhao <zhaoshenglong@...wei.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"Ian.Campbell@...rix.com" <Ian.Campbell@...rix.com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"ard.biesheuvel@...aro.org" <ard.biesheuvel@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"leif.lindholm@...aro.org" <leif.lindholm@...aro.org>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	"julien.grall@...rix.com" <julien.grall@...rix.com>,
	"freebsd-arm@...ebsd.org" <freebsd-arm@...ebsd.org>,
	"matt.fleming@...el.com" <matt.fleming@...el.com>,
	"christoffer.dall@...aro.org" <christoffer.dall@...aro.org>,
	"jbeulich@...e.com" <jbeulich@...e.com>,
	"peter.huangpeng@...wei.com" <peter.huangpeng@...wei.com>,
	"shannon.zhao@...aro.org" <shannon.zhao@...aro.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"daniel.kiper@...cle.com" <daniel.kiper@...cle.com>
Subject: Re: [PATCH] efi/libstub/fdt: Standardize the names of EFI stub
 parameters

> > C) When you could go:
> > 
> >    DT -> Discover Xen -> Xen-specific stuff -> Xen-specific EFI/ACPI discovery
> 
> I take you mean discovering Xen with the usual Xen hypervisor node on
> device tree. I think that C) is a good option actually. I like it. Not
> sure why we didn't think about this earlier. Is there anything EFI or
> ACPI which is needed before Xen support is discovered by
> arch/arm64/kernel/setup.c:setup_arch -> xen_early_init()?

Currently lots (including the memory map). With the stuff to support
SPCR, the ACPI discovery would be moved before xen_early_init().

> If not, we could just go for this. A lot of complexity would go away.

I suspect this would still be fairly complex, but would at least prevent
the Xen-specific EFI handling from adversely affecting the native case.

> > D) If you want to be generic:
> >    EFI -> EFI application -> EFI tables -> ACPI tables -> Xen-specific stuff
> >           \------------------------------------------/
> > 	   (virtualize these, provide shims to Dom0, but handle
> > 	    everything in Xen itself)
> 
> I think that this is good in theory but could turn out to be a lot of
> work in practice. We could probably virtualize the RuntimeServices but
> the BootServices are troublesome.

What's troublesome with the boot services?

What can't be simulated?

> > E) Partially-generic option:
> >    EFI -> EFI application -> Xen detected by registered GUID -> Xen-specific EFI bootloader stuff -> OS in Xen-specific configuration
> > 
> > 
> > > > > In any case this should be separate from the shim ABI discussion.
> > > > 
> > > > I disagree; I think this is very much relevant to the ABI discussion.
> > > > That's not to say that I insist on a particular approach, but I think
> > > > that they need to be considered together.
> > > 
> > > Let's suppose Xen didn't expose any RuntimeServices at all, would that
> > > make it easier to discuss about the EFI stub parameters?
> > 
> > It would simply the protocol specific to Xen, certainly.
> > 
> > > In the grant scheme of things, they are not that important, as Ian
> > > wrote what is important is how to pass the RSDP.
> > 
> > Unfortunately we're still going to have to care about this eventually,
> > even if for something like kexec. So we still need to spec out the state
> > of things if this is going to be truly generic.
>  
> Fair enough. My position is that if we restrict this to RuntimeServices,
> it might be possible, but I still prefer C).

Regardless of what we do we still need a well-defined state here, which
brings us back to the initial problem eventually.

Thanks,
Mark.
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