Re: [PATCH 1/1] Xen PV support for hugepages

["Jan Beulich" <jbeulich@novell.com>]

>>> Dave McCracken <dcm@mccr.org> 06.11.08 14:44 >>>
>> Finally, no longer hiding X86_FEATURE_PSE from the guest seems rather
>> risky: I'm pretty sure the pv-ops kernel relies on this flag being clear -
>> when set, it would blindly (i.e. without ensuring the underlying memory is
>> contiguous and suitably aligned) try to use 2Mb mappings for e.g. the 1:1
>> mapping. I would think this capability ought to be propagated by another
>> means. Likewise I'm uncertain about letting X86_CR4_PSE shine through.
>>
>> And a general question: How is a trivial DomU going to be able to make
>> use of this, without being permitted to allocate non-order-zero chunks of
>> memory?
>
>This is the point of having hugepages a command line option.  It should only 
>be turned on if you intend to run guests who enforce the alignment rules.  

You mean 'if you intend to run *only* guests ...', including dom0. Any guest
unaware of the connection of X86_FEATURE_PSE and the need to create
contiguous 2M chunks would fail, and any guest not having I/O memory
assigned would never manage to create such chunks.

Jan