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

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Message-ID: <m14pmspeqk.fsf@ebiederm.dsl.xmission.com>
Date:	Fri, 04 May 2007 13:31:47 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>, 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>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 1/3] Replace paravirt_probe with "platform type" boot header field

"H. Peter Anvin" <hpa@...or.com> writes:

> Indeed.  I think, yes, what has been there up to now has pretty much
> been at least in part experimental, and I fear there will be unavoidable
> breakage as part of sanitizing it.  C'est la vie, I guess.

The one significant one I left out I think is the VISWS.  I'm not certain
what we do there, but I know it never went through setup.S

Yes.  At the same time we have been sufficiently disciplined (baring
paravirt) that the changes should be quite small, and we have a big
enough sample size now that we can pretty clearly see ways in which
the code will vary.

>>>> And 4K seems to be our maximum size for backwards compatibility.  Although
>>>> we use it in a fairly sparse way, so we should be ok.
>>> Sort of.  It's pretty full.
>> 
>> True.  For small little extensions we have room.  For big things probably
>> not.
>
> For big extensions we'll probably have to go the pointer route already
> done with the command line.

Likely.  It is tricky because if we actually have to do a normal BIOS
query to get it things a little sticky, because we can't allocate
memory.  Hmm.  It looks like we need a way to export the size of
our parameter area to the bootloader.  We have setup_sects for 16bit
real mode bootloaders and that should be good enough, but we need
something equivalent for the 32bit entry point.

Requirements analysis here we come.

Eric
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