linux-kernel - Re: [RFC v1 4/8] x86/init: add linker table support

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Date:	Thu, 21 Jan 2016 11:25:41 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Roger Pau Monné <roger.pau@...rix.com>,
	"Luis R. Rodriguez" <mcgrof@...not-panic.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Andy Lutomirski <luto@...capital.net>, mcb30@...e.org,
	Juergen Gross <jgross@...e.com>,
	Jan Beulich <JBeulich@...e.com>, joro@...tes.org,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	andreyknvl@...gle.com, long.wanglong@...wei.com,
	qiuxishi@...wei.com, aryabinin@...tuozzo.com,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Valentin Rothberg <valentinrothberg@...il.com>,
	Peter Senna Tschudin <peter.senna@...il.com>,
	X86 ML <x86@...nel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC v1 4/8] x86/init: add linker table support

On 01/21/16 05:45, Boris Ostrovsky wrote:
>> I don't think the hypervisor should be setting Linux specific boot
>> related parameters, the boot ABI should be OS agnostic. IMHO, a small
>> shim should be added to Linux in order to set what Linux requires when
>> entering from a Xen entry point.

For the record, this is exactly what hardware_subarch is meant to do:
revector to a stub to do this kind of setup, for a subarchitecture which
doesn't have a natural stub like BIOS or EFI.  In the case of Xen PV, or
lguest, there are special care that has to be done very early in the
path due to the nonstandard handling of page tables, which is another
reason for this field.

> And that's exactly what HVMlite does. Most of this shim layer is setting
> up boot_params, after which we jump to standard x86 boot path (i.e.
> startup_{32|64}). With hardware_subarch set to zero.

Which is the way to do it as long as the early code can be the same.

	-hpa