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Re: [Xen-devel] Baffled by multipage_allocation_permitted()

To: "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx>, "Dave McCracken" <dcm@xxxxxxxx>
Subject: Re: [Xen-devel] Baffled by multipage_allocation_permitted()
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Tue, 16 Jun 2009 10:19:46 +0100
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>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 15.06.09 23:57 >>>
>On 15/06/2009 22:44, "Dave McCracken" <dcm@xxxxxxxx> wrote:
>
>> #define multipage_allocation_permitted(d)   \
>>    (!rangeset_is_empty((d)->iomem_caps) || \
>>     !rangeset_is_empty((d)->arch.ioport_caps))
>> 
>> I had never tracked down the significance of this macro since it didn't 
>> appear
>> to be an issue.  Now it's suddenly denying me the ability to work in 2M 
>> pages.
>> 
>> What is this macro trying to achieve?  Why is it necessary?  Is there any
>> compelling reason we can't just remove it and allow multipage allocations 
>> from
>> any domain?
>
>We can just get rid of it I think. There are arguably worse other things we
>already allow, like any guest can allocate low memory by specifying a small
>value of XENMEMF_address_bits().

Wouldn't it be better to tighten things rather than relaxing them?

Jan


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