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Re: [Xen-devel] xen does not see more than 173800500k of memory

To: Jan Beulich <jbeulich@xxxxxxxxxx>, Susan Krysan <KRYSANS@xxxxxxxxxx>
Subject: Re: [Xen-devel] xen does not see more than 173800500k of memory
From: Keir Fraser <keir@xxxxxxxxxxxxx>
Date: Thu, 23 Aug 2007 16:53:16 +0100
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It's not a Xen security risk though. If you happen to use a compat guest
with page flipping then it just won't work. I think it's fair to say at this
point that that is just 'too bad'. If anyone really cares then they will
need to add a copy-to-low-memory path in Xen's page transfer code. The 166GB
restriction has to go.

 -- Keir

On 23/8/07 15:51, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

>>>> Keir Fraser <keir@xxxxxxxxxxxxx> 23.08.07 16:27 >>>
>> This should be easily fixed by properly applying
>> domain_clamp_alloc_bitsize() in __alloc_domheap_pages(). Why is it only
>> applied when the bitsize is explicitly specified by the caller?
>> 
>> I think that's the only thing to fix to allow the 166GB boot-time
>> restriction to be lifted, but am I missing something, Jan?
> 
> We had this discussion before - the problem is not restricting the allocations
> a domain does, but pages getting passed to it from other domains, which (if
> they happen to lie outside the 166Gb range) the domain then can't control.
> And yes, you said page flipping is basically dead, but this isn't being
> enforced (and probably can't as long as you want to support older guests
> potentially using it).
> 
> Jan
> 
> 
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