Bug#903767: Stretch kernel 4.9.110-1 boot-loops with Xen Hypervisor 4.8

["Michael J. Redd" <micredd@gmail.com>]

This also apparently affects at least PV guests. Upgrading a PV domU to
 kernel 4.9.110-1 and rebooting yields the following output via xl's
console:


Loading Linux 4.9.0-6-amd64 ...
Loading Linux 4.9.0-7-amd64 ...
Loading initial ramdisk ...   [ vmlinuz-4.9.0-7-
amd6  2.69MiB  66%  1.67MiB/s ]
[    0.128044] dmi: Firmware registration
failed.a  17.29MiB  100%  9.75MiB/s ]
[    1.408778] dmi-sysfs: dmi entry is absent.
[    1.427758] general protection fault: 0000 [#1] SMP
[    1.427767] Modules linked in:
[    1.427778] CPU: 0 PID: 1 Comm: init Not tainted 4.9.0-7-amd64 #1
Debian 4.9.110-1
[    1.427789] task: ffff88000ee36040 task.stack: ffffc90040068000
[    1.427798] RIP: e030:[<ffffffff81614d4d>]  [<ffffffff81614d4d>]
ret_from_fork+0x2d/0x70
[    1.427815] RSP: e02b:ffffc9004006bf50  EFLAGS: 00010006
[    1.427823] RAX: 00000002175f5000 RBX: ffffffff816076d0 RCX:
ffffea0000310e1f
[    1.427833] RDX: 0000000000000002 RSI: 0000000000000002 RDI:
ffffc9004006bf58
[    1.427840] RBP: 0000000000000000 R08: 0000000000000000 R09:
ffff88000a9e5000
[    1.427847] R10: 8080808080808080 R11: fefefefefefefeff R12:
0000000000000000
[    1.427854] R13: 179f3966a73fde7b R14: 06f99905e8f3edfb R15:
cf60f5f9fd8e4751
[    1.427866] FS:  0000000000000000(0000) GS:ffff88000fc00000(0000)
knlGS:0000000000000000
[    1.427873] CS:  e033 DS: 0000 ES: 0000 CR0: 0000000080050033
[    1.427879] CR2: 00007ffd37e72eb9 CR3: 000000000a9f4000 CR4:
0000000000042660
[    1.427889] Stack:
[    1.427893]  0000000000000000 0000000000000000 0000000000000000
0000000000000000
[    1.427906]  0000000000000000 0000000000000000 0000000000000000
0000000000000000
[    1.427921]  0000000000000000 0000000000000000 0000000000000000
0000000000000000
[    1.427943] Call Trace:
[    1.427951] Code: c7 e8 b8 fe a8 ff 48 85 db 75 2f 48 89 e7 e8 5b ed
9e ff 50 90 0f 20 d8 65 48 0b 04 25 e0 02 01 00 78 08 65 88 04 25 e7 02
01 00 <0f> 22 d8 58 66 66 90 66 66 90 e9 c1 07 00 00 4c 89 e7 eb 11 e8 
[    1.428148] RIP  [<ffffffff81614d4d>] ret_from_fork+0x2d/0x70
[    1.428160]  RSP <ffffc9004006bf50>
[    1.428168] ---[ end trace cb1a96e88a7c4794 ]---
[    1.428298] Kernel panic - not syncing: Attempted to kill init!
exitcode=0x0000000b
[    1.428298] 
[    1.428316] Kernel Offset: disabled


Note that the guest bootloader being used here is pvGRUB; not sure if
that is relevant but thought I would include it. Similarly, rolling the
domU back to the previous kernel/selecting the previous kernel via
pvGRUB allows the VM to boot normally.