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Re: [Xen-devel] conditional clearing of dom0_l2 in i386's zap_low_mappin

To: "Keir Fraser" <keir@xxxxxxx>
Subject: Re: [Xen-devel] conditional clearing of dom0_l2 in i386's zap_low_mappings() ?
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Fri, 29 Oct 2010 07:51:15 +0100
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>>> On 28.10.10 at 18:06, Keir Fraser <keir@xxxxxxx> wrote:
> On 28/10/2010 16:49, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
>>>>> On 28.10.10 at 17:30, Keir Fraser <keir@xxxxxxx> wrote:
>>> On 28/10/2010 15:50, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
>>>> What is the reason for not unconditionally clearing the whole L2
>>>> directory here? There shouldn't be anything in the first Gb that
>>>> wasn't placed there just temporarily by Xen...
>>> You mean the conditional within the for loop that clears dom0 l2 entries? If
>>> we zapped all of dom0's l2 entries, we'd also be zapping the entries
>>> legitimately just created by the dom0 builder!
>> Oh, I didn't look closely enough. I actually just meant all the
>> entries in the first of the four L2 tables.
> Oh I see. Well possibly. But you might still need the conditional for the
> other three slots anyway, so it wouldn't be a simplification in that case.

I'm not after a simplification really. I'm trying to eliminate some
restrictions on initrd size (as well as possible collisions between
the various memory areas used during early boot), and in the
process I need to switch the 1:1 mapping of the first Gb to a
more flexible model (the target is x86-64, but to avoid adding
more conditionals in the Dom0 building code I prefer to do the
same to i386 too).

I was just asking because I may need to flush out temporary
mappings in Dom0's first L2 that wouldn't match those under
idle_page_table_l2[0] (though right now I think I may get away
without having to).


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