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

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Message-ID: <alpine.DEB.2.02.1509111410180.2672@kaball.uk.xensource.com>
Date:	Fri, 11 Sep 2015 14:14:09 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Daniel Kiper <daniel.kiper@...cle.com>
CC:	Mark Rutland <mark.rutland@....com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	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>
Subject: Re: [PATCH] efi/libstub/fdt: Standardize the names of EFI stub
 parameters

On Fri, 11 Sep 2015, Daniel Kiper wrote:
> On Thu, Sep 10, 2015 at 05:23:02PM +0100, Mark Rutland wrote:
> > > > 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?
> 
> How do you want to access bare metal EFI boot services from dom0 if they
> were shutdown long time ago before loading dom0 image? What do you need
> from EFI boot services in dom0?

That's right. Trying to emulate BootServices after the real
ExitBootServices has already been called seems like a very bad plan.

I think that whatever interface we come up with, would need to be past
ExitBootServices.
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