Unfortunately I have not yet figured out why this happens, but can confirm by
compiling with or without CONFIG_RANDOMIZE_BASE being set that without KASLR all
is ok, but with it enabled there are issues (actually a dom0 does not even boot
as a follow up error).

Details can be seen in [1] but basically this is always some portion of a
vmalloc allocation failing after hitting a freshly allocated PTE space not being
PTE_NONE (usually from a module load triggered by systemd-udevd). In the
non-dom0 case this repeats many times but ends in a guest that allows login. In
the dom0 case there is a more fatal error at some point causing a crash.

I have not tried this for a normal PV guest but for dom0 it also does not help
to add "nokaslr" to the kernel command-line.

-Stefan

19:35:02 [ 2.547049] ------------[ cut here ]------------
19:35:02 [ 2.547065] WARNING: CPU: 0 PID: 97 at
/build/buildd/linux-3.16.0/mm/vmalloc.c:128 vmap_page_range_noflush+0x2d1/0x370()
19:35:02 [ 2.547069] Modules linked in:
19:35:02 [ 2.547073] CPU: 0 PID: 97 Comm: systemd-udevd Not tainted
3.16.0-6-generic #11-Ubuntu
19:35:02 [ 2.547077] 0000000000000009 ffff880002defb98 ffffffff81755538
0000000000000000
19:35:02 [ 2.547082] ffff880002defbd0 ffffffff8106bb0d ffff88000400ec88
0000000000000001
19:35:02 [ 2.547086] ffff880002fcfb00 ffffffffc0391000 0000000000000000
ffff880002defbe0
19:35:02 [ 2.547090] Call Trace:
19:35:02 [ 2.547096] [<ffffffff81755538>] dump_stack+0x45/0x56
19:35:02 [ 2.547101] [<ffffffff8106bb0d>] warn_slowpath_common+0x7d/0xa0
19:35:02 [ 2.547104] [<ffffffff8106bbea>] warn_slowpath_null+0x1a/0x20
19:35:02 [ 2.547108] [<ffffffff81197c31>] vmap_page_range_noflush+0x2d1/0x370
19:35:02 [ 2.547112] [<ffffffff81197cfe>] map_vm_area+0x2e/0x40
19:35:02 [ 2.547115] [<ffffffff8119a058>] __vmalloc_node_range+0x188/0x280
19:35:02 [ 2.547120] [<ffffffff810e92b4>] ? module_alloc_update_bounds+0x14/0x70
19:35:02 [ 2.547124] [<ffffffff810e92b4>] ? module_alloc_update_bounds+0x14/0x70
19:35:02 [ 2.547129] [<ffffffff8104f294>] module_alloc+0x74/0xd0
19:35:02 [ 2.547132] [<ffffffff810e92b4>] ? module_alloc_update_bounds+0x14/0x70
19:35:02 [ 2.547135] [<ffffffff810e92b4>] module_alloc_update_bounds+0x14/0x70
19:35:02 [ 2.547146] [<ffffffff810e9a6c>] layout_and_allocate+0x74c/0xc70
19:35:02 [ 2.547149] [<ffffffff810ea063>] load_module+0xd3/0x1b70
19:35:02 [ 2.547154] [<ffffffff811cfeb1>] ? vfs_read+0xf1/0x170
19:35:02 [ 2.547157] [<ffffffff810e7aa1>] ? copy_module_from_fd.isra.46+0x121/0x180
19:35:02 [ 2.547161] [<ffffffff810ebc76>] SyS_finit_module+0x86/0xb0
19:35:02 [ 2.547167] [<ffffffff8175de7f>] tracesys+0xe1/0xe6
19:35:02 [ 2.547169] ---[ end trace 8a5de7fc66e75fe4 ]---
19:35:02 [ 2.547172] vmalloc: allocation failure, allocated 20480 of 24576 bytes
19:35:02 [ 2.547175] systemd-udevd: page allocation failure: order:0, mode:0xd2


[1] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1350522