linux-kernel - Re: [RFC PATCH 1/3] Replace paravirt_probe with "platform type" boot header field

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Date:	Fri, 04 May 2007 08:01:39 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Andi Kleen <ak@...e.de>, Chris Wright <chrisw@...s-sol.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Zachary Amsden <zach@...are.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 1/3] Replace paravirt_probe with "platform type" boot header field

Rusty Russell <rusty@...tcorp.com.au> writes:

> [ This patch won't apply, even to -mm: it comes after the documentation
> patch.  But it's hopefully readable ]
>
> 1) This code assumes that 0x23C is going to be the "platform type"
>    field of the next version of the Linux boot header format.
>
> 2) This doesn't actually assume that P=V, but unlike the paravirt
>    probe code doesn't assume that V=P+PAGE_OFFSET either.
>
> The following patch actually fixes up lguest to boot with P=V.

We should place that initial branch right after startup_32,
we don't need the startup_paravirt at all now.

ENTRY(startup_32)
#ifdef CONFIG_LGUEST_GUEST
        cmpl	$1, 0x23c(%esi)
	je      lguest_init
#endif

...

Although it might make sense to do:
ENTRY(startup_32)
	cmpl	$0, 0x23c(%esi)
        jnz	startup_subarch

To get the branches out of the main flow of execution but
that is minor.  This isn't a performance critical path.

Eric
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