Update grub freezes when copying host CPU configuration

[Marcelo Cerri]

Currently when using linux-kvm (4.4.0-1013 or 4.4.0-1015), if the virtual machine is configured to copy the host CPU configuration, `update-grub` freezes and never completes (that's also true when installing a new kernel).

These are the guest CPU flags (from /proc/cpuinfo) when copying the host CPU configuration:

flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ss syscall nx pdpe1gb rdtscp lm constant_tsc rep_good nopl pni pclmulqdq vmx ssse3 fma cx16 pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes avx f16c rdrand hypervisor lahf_lm abm invpcid_single tpr_shadow vnmi flexpriority ept vpid fsgsbase bmi1 avx2 smep bmi2 erms invpcid arat

.. And when using the Hypervisor defaults (that's the scenario where the issue does not happen):

flags : fpu de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pse36 clflush mmx fxsr sse sse2 syscall nx lm rep_good nopl pni vmx cx16 x2apic hypervisor lahf_lm tpr_shadow vnmi flexpriority ept vpid

Also, when copying the host CPU configuration, the following stack trace is shown during boot:

--->8---
Begin: Loading essential drivers ... done.
Begin: Running /scripts/init-premount ... done.
Begin: Mounting root file system ... Begin: Running /scripts/local-top ... done.
Begin: Running /scripts/local-premount ... [ 1.899866] raid6: sse2x1 gen() 6551 MB/s
[ 1.967889] raid6: sse2x1 xor() 5061 MB/s
[ 2.035882] raid6: sse2x2 gen() 5855 MB/s
[ 2.103866] raid6: sse2x2 xor() 5538 MB/s
[ 2.171867] raid6: sse2x4 gen() 9813 MB/s
[ 2.239875] raid6: sse2x4 xor() 6767 MB/s
[ 2.243885] invalid opcode: 0000 [#1] SMP
[ 2.244520] Modules linked in: raid6_pq(+)
[ 2.245129] CPU: 0 PID: 235 Comm: modprobe Not tainted 4.4.0-1015-kvm #20-Ubuntu
[ 2.245989] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
[ 2.246881] task: ffff88001f58eb40 ti: ffff88001f5b0000 task.ti: ffff88001f5b0000
[ 2.247563] RIP: 0010:[<ffffffffc03ab9f1>] [<ffffffffc03ab9f1>] 0xffffffffc03ab9f1
[ 2.248333] RSP: 0018:ffff88001f5b3bd0 EFLAGS: 00010246
[ 2.248865] RAX: 0000000000000001 RBX: ffff88001f5b3c10 RCX: 00000000fffedd22
[ 2.249547] RDX: ffff88001f5b3c10 RSI: 0000000000001000 RDI: 0000000000000012
[ 2.250222] RBP: 0000000000000012 R08: 000000000000000a R09: 0000000000000124
[ 2.250946] R10: ffff88001f695fd0 R11: 0000000000000124 R12: 0000000000001000
[ 2.251764] R13: ffff88001f694000 R14: ffff88001f695000 R15: 0000000000000080
[ 2.252684] FS: 00007f3335cd0700(0000) GS:ffff88001fc00000(0000) knlGS:0000000000000000
[ 2.253767] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2.254558] CR2: 00007ffd707ba398 CR3: 000000001f6a8000 CR4: 0000000000120630
[ 2.255548] Stack:
[ 2.255852] ffffffffc03be4a0 0000000000000001 0000000000003624 0000000000002741
[ 2.256997] ffff88001f694000 ffffffffc03abf38 ffffffffc03c110e 00000000fffedd22
[ 2.258137] ffffffffc03ae300 ffffffffc03af300 ffffffffc03b0300 ffffffffc03b1300
[ 2.259296] Call Trace:
[ 2.259666] [<ffffffffc03c110e>] ? 0xffffffffc03c110e
[ 2.260174] [<ffffffffc03c1000>] ? 0xffffffffc03c1000
[ 2.260681] [<ffffffff97c00414>] ? 0xffffffff97c00414
[ 2.261166] [<ffffffff97cb2732>] ? 0xffffffff97cb2732
[ 2.261671] [<ffffffff97c92dee>] ? 0xffffffff97c92dee
[ 2.262165] [<ffffffff97c91110>] ? 0xffffffff97c91110
[ 2.262672] [<ffffffff97c913e3>] ? 0xffffffff97c913e3
[ 2.263208] [<ffffffff97c93110>] ? 0xffffffff97c93110
[ 2.263709] [<ffffffff9800e8d5>] ? 0xffffffff9800e8d5
[ 2.264237] Code: 98 41 56 48 83 c0 01 41 55 4c 8d 3c c5 00 00 00 00 41 54 49 89 f4 55 89 fd 53 48 89 d3 4c 8b 2c c2 4e 8b 74 3a 08 e8 4f 2d 87 d7 <c5> fd 6f 05 27 2c 01 00 c5 e5 ef db 4d 85 e4 0f 84 a7 00 00 00
[ 2.268055] RIP [<ffffffffc03ab9f1>] 0xffffffffc03ab9f1
[ 2.268593] RSP <ffff88001f5b3bd0>
[ 2.268959] ---[ end trace f633f39e1b0e512e ]---
Segmentation fault
done.
Warning: fsck not present, so skipping root file system
--->8---