linux-kernel - Re: [PATCH 23/25] [PATCH] paravirt hooks for arch initialization

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Message-ID: <46BCC6DF.2040301@redhat.com>
Date:	Fri, 10 Aug 2007 17:13:19 -0300
From:	Glauber de Oliveira Costa <gcosta@...hat.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>, ak@...e.de
CC:	Glauber de Oliveira Costa <glommer@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, lguest@...abs.org,
	linux-kernel@...r.kernel.org, chrisw@...s-sol.org,
	anthony@...emonkey.ws, Steven@...p2.linux-foundation.org,
	akpm@...ux-foundation.org,
	virtualization@...ts.linux-foundation.org, mingo@...e.hu,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 23/25] [PATCH] paravirt hooks for arch initialization

Jeremy Fitzhardinge escreveu:
> Glauber de Oliveira Costa wrote:
>> I think the idea you gave me earlier of using probe_kernel_address could
>> work. Xen/lguest/put_yours_here that won't use an ebda would then have
>> to unmap the page, to make sure a read would fault.
> 
> Hm, the memory might be mapped anyway, but we could make sure its all
> zero.  discover_ebda should be able to deal with that OK.
> 
>     J
Indeed, as the EBDA_ADDR_POINTER is not aligned, this may work even better.

It seems to me safe to assume that if we read zero on that line:

ebda_addr = *(unsigned short *)__va(EBDA_ADDR_POINTER);

We could just do ebda_size = 0 and go home happy, skipping the rest of 
the process.

Andi, are you okay with it ?

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