[BISECTED REGRESSION] v4.0+ KVM: x86: allow TSC deadline timer on all hosts

["Matwey V. Kornilov" <matwey.kornilov@gmail.com>]

Hello,

I've bisected that commit defcf51fa93929bd ("KVM: x86: allow TSC
deadline timer on all hosts") makes guest kernels crash under specific
circumstances.
The issue itself is the following. I use host linux kernel (was
bisected) to run guest linux kernels using qemu-kvm (version 2.3.1.
earlier version 2.1 has also been checked and found demonstrating the
same behavior)

I've found that

1) the following qemu command

qemu-system-x86_64 -machine accel=kvm -nodefaults -no-reboot
-nographic -cpu host -vga none  -kernel kernel  -initrd initrd -append
'panic=1 no-kvmclock console=ttyS0 loglevel=7' -m 1024 -serial stdio

successfully boots the guest kernel when host kernel version is prior
defcf51fa93929bd (3.16 3.18 3.19 was checked)

2) the same command leads to the guest kernel failure with the same
qemu binary and the same kernel and initrd images when host kernel
4.0+ is used (4.0 4.4 4.9 was checked):

[    0.588000] divide error: 0000 [#1] SMP
[    0.588000] Modules linked in:
[    0.588000] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G        W
3.16.6-2-default #1
[    0.588000] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS rel-1.8.1-0-g4adadbd-20150316_085822-nilsson.home.kraxel.org
04/01/2014
[    0.588000] task: ffff88003d61e010 ti: ffff88003d63c000 task.ti:
ffff88003d63c000
[    0.588000] RIP: 0010:[<ffffffff810c6e7f>]  [<ffffffff810c6e7f>]
clockevents_config.part.3+0x1f/0xa0
[    0.588000] RSP: 0000:ffff88003d63fe90  EFLAGS: 00010246
[    0.588000] RAX: ffffffffffffffff RBX: ffff88003f80ce80 RCX: 0000000000000000
[    0.588000] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffffffffffff
[    0.588000] RBP: 000000000000b060 R08: 0000000000000001 R09: ffffffff81ee84b0
[    0.588000] R10: 00000000000000bb R11: 0000000000000003 R12: 000000000000b0a0
[    0.588000] R13: 0000000000000200 R14: 0000000000000000 R15: 0000000000000000
[    0.588000] FS:  0000000000000000(0000) GS:ffff88003f800000(0000)
knlGS:0000000000000000
[    0.588000] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[    0.588000] CR2: 00000000ffffffff CR3: 0000000001c13000 CR4: 00000000000006f0
[    0.588000] Stack:
[    0.588000]  ffff88003f80ce80 000000000000b060 000000000000b0a0
ffffffff810c73cc
[    0.588000]  0000000000000000 ffffffff81d15952 ffffffff81e63338
0000000000000000
[    0.588000]  0000000000000000 0000000000000000 ffffffff81d0910c
0000000000000000
[    0.588000] Call Trace:
[    0.588000]  [<ffffffff810c73cc>] clockevents_config_and_register+0x1c/0x30
[    0.588000]  [<ffffffff81d15952>] native_smp_prepare_cpus+0x3a1/0x3d0
[    0.588000]  [<ffffffff81d0910c>] kernel_init_freeable+0xc1/0x202
[    0.588000]  [<ffffffff815bc04a>] kernel_init+0xa/0xf0
[    0.588000]  [<ffffffff815d0b7c>] ret_from_fork+0x7c/0xb0
[    0.588000] Code: 66 66 66 2e 0f 1f 84 00 00 00 00 00 66 66 66 66
90 41 54 31 d2 89 f1 89 f6 41 b8 01 00 00 00 55 53 48 89 fb 48 8b 7f
70 48 89 f8 <48> f7 f6 48 85 c0 74 0b 48 3d 58 02 00 00 41 89 c0 77 4e
4c 8d
[    0.588000] RIP  [<ffffffff810c6e7f>] clockevents_config.part.3+0x1f/0xa0
[    0.588000]  RSP <ffff88003d63fe90>
[    0.592000] ---[ end trace 6dcb37223984f47d ]---
[    0.596000] Kernel panic - not syncing: Attempted to kill init!
exitcode=0x0000000b

As soon as the guest kernel were bootable before in this
configuration, I think this could be a regression. But I am not sure
how the commit exactly affects the behavior.

I've also tried to understand what was happening inside the guest
kernel native_calibrate_tsc() function. Nothing interesting except
that both tsc1 and tsc2 are ULLONG_MAX after the for loop.

References: https://bugzilla.opensuse.org/show_bug.cgi?id=1023358

-- 
With best regards,
Matwey V. Kornilov
http://blog.matwey.name
xmpp://0x2207@jabber.ru