[wily] squashfs decompression failures on Xen HVM guest

[Stefan Bader]

Base: Desktop 64bit installation ISO
Guest: Xen HVM, 2 vCPUs, 1/2/4 G memory

The wily desktop install iso fails to boot into the GUI lightdm selection screen because of squashfs decompression failures. This happens with 1 and 2 GB of virtual memory. 4 GB succeeds. Using KVM with a comparable setup shows no issues with 1 and 2 GB of memory.

Normally KVM guests may differ in the number of hotplug CPUs but I tried with 2GB memory and 128 possible CPUs as KVM guest and that worked as well.

The Vivid desktop iso will successfully start as Xen HVM guest with 2G of memory (have not tried 1G there yet). I also tried Vivid as host (Xen version and dom0 kernel) with the same results. So it seems to be an issue with the wily iso. So it seems to be something in the Wily kernel.

Memory layout did not look wrong. At least I could see no difference in the e820 tables of a Vivid (3.19) and a Wily (4.2) kernel. Also looks roughly the same as for a KVM boot.