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

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Date:	Fri, 10 Aug 2007 16:17:25 -0300
From:	Glauber de Oliveira Costa <gcosta@...hat.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
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
Subject: Re: [PATCH 23/25] [PATCH] paravirt hooks for arch initialization

Jeremy Fitzhardinge escreveu:
> Glauber de Oliveira Costa wrote:
>> On 8/9/07, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
>>   
>>>> What's the EBDA actually used for?  The only place which seems to use
>>>> ebda_addr is in the e820 code to avoid that area as RAM.
>>>>       
>>> It belongs to the firmware.
>>>     
>> Wouldn't it be better, then, to just skip this step unconditionally if
>> we are running a paravirtualized guest? What do we from doing it?
>>   
> 
> It's better to make discover_ebda() quietly cope with a missing ebda for
> whatever reason.  We could add an explicit interface to paravirt_ops to
> handle this one little corner, but it isn't very important, not very
> general and really its just clutter.  Its much better to have things
> cope with being virtualized quietly on their own rather than hit them
> all with the pv_ops hammer.   pv_ops is really for things where the
> hypervisor-specific code really has to get actively involved.
> 
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.


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