I got a hard failure on AWS m1.small, while running the seccomp tests:

 * Starting xinetd daemon
    [74G[ OK ]
[ 3726.335940] general protection fault: 0000 [#1] SMP 
[ 3726.335961] Modules linked in: iptable_filter ip_tables x_tables acpiphp [last unloaded: signpost]
[ 3726.335976] 
[ 3726.335981] Pid: 24386, comm: seccomp_tests Not tainted 3.0.0-23-virtual #39-Ubuntu  
[ 3726.335992] EIP: 0061:[<c010372d>] EFLAGS: 00010202 CPU: 0
[ 3726.336004] EIP is at xen_write_cr4+0xd/0x20
[ 3726.336010] EAX: 00000664 EBX: 00000016 ECX: c08b4740 EDX: 00000000
[ 3726.336010] ESI: eb011980 EDI: b76e4bb0 EBP: eb00ff60 ESP: eb00ff60
[ 3726.336010]  DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0069
[ 3726.336010] Process seccomp_tests (pid: 24386, ti=eb00e000 task=eb011980 task.ti=eb00e000)
[ 3726.336010] Stack:
[ 3726.336010]  eb00ff68 c0110bc6 eb00ff70 c01116f5 eb00ff7c c01b6868 00000001 eb00ffac
[ 3726.336010]  c01676cc b76e4bb0 00000000 c10a0680 000003e8 eb00ffac c016646a 4a13f267
[ 3726.336010]  00000016 b76e4bb0 00000000 eb00e000 c065f644 00000016 00000001 0804bd41
[ 3726.336010] Call Trace:
[ 3726.336010]  [<c0110bc6>] hard_disable_TSC+0x16/0x20
[ 3726.336010]  [<c01116f5>] disable_TSC+0x25/0x30
[ 3726.336010]  [<c01b6868>] prctl_set_seccomp+0x38/0x60
[ 3726.336010]  [<c01676cc>] sys_prctl+0xbc/0x300
[ 3726.336010]  [<c016646a>] ? sys_setresuid+0x10a/0x150
[ 3726.336010]  [<c065f644>] syscall_call+0x7/0xb
[ 3726.336010] Code: e5 3e 8d 74 26 00 5d c3 8d b6 00 00 00 00 55 89 e5 3e 8d 74 26 00 31 c0 5d c3 8d 74 26 00 55 89 e5 3e 8d 74 26 00 25 6f ff fb ff <0f> 22 e0 5d c3 8d b4 26 00 00 00 00 8d bc 27 00 00 00 00 55 89 
[ 3726.336010] EIP: [<c010372d>] xen_write_cr4+0xd/0x20 SS:ESP 0069:eb00ff60
[ 3726.336259] ---[ end trace d66d75245de68efa ]---
[ 3726.337986] general protection fault: 0000 [#2] SMP 
[ 3726.337997] Modules linked in: iptable_filter ip_tables x_tables acpiphp [last unloaded: signpost]
[ 3726.338011] 
[ 3726.338016] Pid: 494, comm: rs:main Q:Reg Tainted: G      D     3.0.0-23-virtual #39-Ubuntu  
[ 3726.338027] EIP: 0061:[<c010372d>] EFLAGS: 00010002 CPU: 0
[ 3726.338033] EIP is at xen_write_cr4+0xd/0x20
[ 3726.338039] EAX: 00000664 EBX: eb011980 ECX: 00000000 EDX: 00000001
[ 3726.338045] ESI: eb016600 EDI: c1388000 EBP: eb00fd74 ESP: eb00fd74
[ 3726.338052]  DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0069
[ 3726.338058] Process rs:main Q:Reg (pid: 494, ti=eb00e000 task=eb016600 task.ti=c1388000)
[ 3726.338065] Stack:
[ 3726.338069]  eb00fd7c c0110bc6 eb00fd9c c011182f eb00fd9c ec693a00 00000000 eb011980
[ 3726.338084]  eb016600 00000000 eb00fdc4 c0109145 0119b000 00000000 eb011c84 00000000
[ 3726.338098]  ec693a00 4a13f267 eb08da00 00000000 c1389e5c c065d237 eb00fe54 00000286
[ 3726.338113] Call Trace:
[ 3726.338119]  [<c0110bc6>] hard_disable_TSC+0x16/0x20
[ 3726.338126]  [<c011182f>] __switch_to_xtra+0x8f/0x130
[ 3726.338134]  [<c0109145>] __switch_to+0x1d5/0x1f0
[ 3726.338141]  [<c065d237>] __schedule+0x2d7/0x620
[ 3726.338149]  [<c0106fae>] ? __raw_callee_save_xen_restore_fl+0x6/0x8
[ 3726.338158]  [<c0151161>] ? vprintk+0x151/0x430
[ 3726.338165]  [<c065f45d>] ? _raw_spin_lock_irqsave+0x2d/0x40
[ 3726.338173]  [<c014a21b>] ? __cond_resched+0x1b/0x30
[ 3726.338180]  [<c065d5f9>] ? _cond_resched+0x29/0x30
[ 3726.338187]  [<c065e770>] ? down_read+0x10/0x1f
[ 3726.338194]  [<c0194684>] ? acct_collect+0x44/0x180
[ 3726.338202]  [<c0154bf9>] ? do_exit+0x2b9/0x3a0
[ 3726.338209]  [<c064b7e0>] ? printk+0x2d/0x2f
[ 3726.338217]  [<c0660886>] ? oops_end+0x96/0xd0
[ 3726.338224]  [<c010caa4>] ? die+0x54/0x80
[ 3726.338231]  [<c0660306>] ? do_general_protection+0xa6/0x220
[ 3726.338239]  [<c0106fae>] ? __raw_callee_save_xen_restore_fl+0x6/0x8
[ 3726.338247]  [<c0660260>] ? default_do_nmi+0x290/0x290
[ 3726.338254]  [<c065fd2f>] ? error_code+0x67/0x6c
[ 3726.338261]  [<c010372d>] ? xen_write_cr4+0xd/0x20
[ 3726.338268]  [<c0110bc6>] ? hard_disable_TSC+0x16/0x20
[ 3726.338275]  [<c01116f5>] ? disable_TSC+0x25/0x30
[ 3726.338282]  [<c01b6868>] ? prctl_set_seccomp+0x38/0x60
[ 3726.338289]  [<c01676cc>] ? sys_prctl+0xbc/0x300
[ 3726.338296]  [<c016646a>] ? sys_setresuid+0x10a/0x150
[ 3726.338303]  [<c065f644>] ? syscall_call+0x7/0xb
[ 3726.338309] Code: e5 3e 8d 74 26 00 5d c3 8d b6 00 00 00 00 55 89 e5 3e 8d 74 26 00 31 c0 5d c3 8d 74 26 00 55 89 e5 3e 8d 74 26 00 25 6f ff fb ff <0f> 22 e0 5d c3 8d b4 26 00 00 00 00 8d bc 27 00 00 00 00 55 89 
[ 3726.338383] EIP: [<c010372d>] xen_write_cr4+0xd/0x20 SS:ESP 0069:eb00fd74
[ 3726.338394] ---[ end trace d66d75245de68efb ]---