linux-kernel - Re: Extending boot protocol & bzImage for paravirt

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Message-ID: <46609636.4050208@zytor.com>
Date:	Fri, 01 Jun 2007 14:57:10 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Chris Wright <chrisw@...s-sol.org>,
	Virtualization Mailing List <virtualization@...ts.osdl.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Extending boot protocol & bzImage for paravirt_ops

Jeremy Fitzhardinge wrote:
> H. Peter Anvin wrote:
>>> Do we care particularly? If 8 bytes is enough for the subarch, do we
>>> care whether its a pointer or literal? After all, this is just a private
>>> channel between the bootloader and some subarch-specific piece of code
>>> in the kernel.
>>>
>>>     
>> I see two options: either we make it a pointer *and a length* so that a
>> loader can reshuffle it at will (that also implies no absolute pointers
>> within the data), or it's an opaque cookie anyway.
> 
> No, it has to be completely opaque.  It might be a pointer to some
> special shared memory or something, and not movable.
> 

Well, if we define is as a movable object then it has to be treated as
such.  It's a protocol definition issue.  If we define it opaque, though
-- of for that matter, if we don't -- we should define what memory it
can live in, though.  Right now, the only "available" memory we have is
end of setup to 0xa0000; the command line is defined to be allocated
from this memory.

	-hpa
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