1GB hugepages and intel_xc_cpuid_policy by default disables it.

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

Hey,

It occured to me that when booting Linux HVM guests, the 1GB hugepage
cpuid is not exposed. One needs to manually do:

 cpuid= ['0x80000001:edx=xxxxx1xxxxxxxxxxxxxxxxxxxxxxxxxx'] 
or 
 cpuid="host,page1gb=k"

(see http://lists.xenproject.org/archives/html/xen-users/2013-09/msg00083.html
for some discussion about it).

The machine I am using is supporting it:

 (XEN) HVM: HAP page sizes: 4kB, 2MB, 1GB 

and this is the only way to get hugepages working
(for reference here is what I have in the guest command line:
"default_hugepagesz=1G hugepagesz=1G hugepages=2 hugepagesz=2M
hugepages=100" and without this cpuid I get:
 hugepagesz: Unsupported page size 1024 M 

because the 1GB flag is not exposed.

I was wondering why we don't check the host cpuid and set the 1GB
flag (pdpe1gb) for those cases? It seems that all the pieces are in
place for this to work?

Thanks!