hugepages support in a XEN virtual guest

• hugepages cannot be used in a paravirtualized XEN guest. RHEL 5 doesn't have this feature enabled. If vm.nr_hugepages is set in RHEL 6 the pages can be allocated, but as soon as they are used the paravirtualized guest will crash.

• hugepages can be used in a fully virtualized (HVM) XEN guest as well as in a KVM environment.

On an fully virtualized guest, it will report the BIOS vendor as "xen" and the System product name will be "HVM domU".

[root@test2 ~]# dmidecode
# dmidecode 2.12
SMBIOS 2.4 present.
10 structures occupying 347 bytes.
Table at 0x000E901F.

Handle 0x0000, DMI type 0, 24 bytes
BIOS Information
    Vendor: Xen
    Version: 3.1.2-371.4.1.el5
    Release Date: 05/07/2013
    Address: 0xE8000
    Runtime Size: 96 kB
    ROM Size: 64 kB
    Characteristics:
        Targeted content distribution is supported
    BIOS Revision: 3.1

Handle 0x0100, DMI type 1, 27 bytes
System Information
    Manufacturer: Red Hat
    Product Name: HVM domU
    Version: 3.1.2-371.4.1.el5
    Serial Number: 4c63d1ea-8876-89a3-d0e7-342fe676a41f
    UUID: 4C63D1EA-8876-89A3-D0E7-342FE676A41F
    Wake-up Type: Power Switch
    SKU Number: Not Specified
    Family: Red Hat Enterprise Linux

On a paravirtualized guest, dmidecode will be empty

[root@test ~]# dmidecode
# dmidecode 2.11
# No SMBIOS nor DMI entry point found, sorry.