Bug 36222

Summary: kvm: 100% CPU usage after 3.0.0-rc1 guest shutdown
Product: Virtualization Reporter: Török Edwin (edwin+bugs)
Component: kvmAssignee: virtualization_kvm
Status: CLOSED CODE_FIX    
Severity: normal CC: alan, avi, florian
Priority: P1    
Hardware: All   
OS: Linux   
Kernel Version: 3.0.0-rc1 Tree: Mainline
Regression: Yes
Attachments: config-3.0.0-rc1
kvm_stat output
trace-cmd record -e kvm; ^C; trace-cmd report

Description Török Edwin 2011-05-30 08:40:23 UTC
Created attachment 60022 [details]
config-3.0.0-rc1

Host is 3.0.0-rc1, guest is 3.0.0-rc1.
After shutting down the guest, KVM on the host uses 100% CPU. 
gdb shows for KVM:
  6 Thread 0x7f00d1875700 (LWP 32105)  0x0000003e278ce2f7 in ioctl () at ../sysdeps/unix/syscall-template.S:82
  5 Thread 0x7f00d1074700 (LWP 32106)  0x0000003e278ce2f7 in ioctl () at ../sysdeps/unix/syscall-template.S:82
  4 Thread 0x7f00d0873700 (LWP 32107)  0x0000003e278ce2f7 in ioctl () at ../sysdeps/unix/syscall-template.S:82
  3 Thread 0x7f00d0072700 (LWP 32108)  0x0000003e278ce2f7 in ioctl () at ../sysdeps/unix/syscall-template.S:82
  2 Thread 0x7f00cf871700 (LWP 32109)  0x0000003e278ce2f7 in ioctl () at ../sysdeps/unix/syscall-template.S:82
* 1 Thread 0x7f00d1e95760 (LWP 32100)  0x0000003e278ceda3 in select () at ../sysdeps/unix/syscall-template.S:82

This seems to be a problem with the 3.0.0-rc1 guest, because if I boot 2.6.39 in the guest (still keeping same 3.0.0-rc1 running on the host), then shutdown completes normally, no 100% CPU usage loop.

.config for KVM guest attached.
KVM command-line (created by libvirt):
/usr/bin/kvm -S -M pc-0.14 -cpu phenom,+wdt,+skinit,+osvw,+3dnowprefetch,+misalignsse,+sse4a,+abm,+cr8legacy,+extapic,+cmp_legacy,+lahf_lm,+rdtscp,+pdpe1gb,+popcnt,+cx16,+ht,+vme -enable-nesting -enable-kvm -m 3072 -smp 5,sockets=5,cores=1,threads=1 -name debian-enc -uuid 55782a0a-937c-fa7b-8db5-86876d151a08 -nodefconfig -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/debian-enc.monitor,server,nowait -mon chardev=charmonitor,id=monitor,mode=readline -rtc base=utc -boot order=c,menu=off -drive file=/var/lib/libvirt/images/debian-enc.img,if=none,id=drive-virtio-disk0,boot=on,format=raw -device virtio-blk-pci,bus=pci.0,addr=0x5,drive=drive-virtio-disk0,id=virtio-disk0 -drive if=none,media=cdrom,id=drive-ide0-1-0,readonly=on,format=raw -device ide-drive,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 -netdev tap,fd=18,id=hostnet0,vhost=on,vhostfd=19 -device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:52:de:54,bus=pci.0,addr=0x3 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -usb -device usb-tablet,id=input0 -vnc 127.0.0.1:0 -vga cirrus -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x6

Bisecting...
Comment 1 Avi Kivity 2011-05-30 08:48:43 UTC
Please also post

- kvm_stat output
- trace-cmd record -e kvm; trace-cmd report
- qemu monitor
    (qemu) info registers
    (qemu) x/40i $eip - 32
Comment 2 Török Edwin 2011-05-30 09:18:31 UTC
Created attachment 60032 [details]
kvm_stat output

when the 100% cpu usage happens
Comment 3 Török Edwin 2011-05-30 09:20:06 UTC
Created attachment 60042 [details]
trace-cmd record -e kvm; ^C; trace-cmd report

(In reply to comment #1)
> Please also post
> 
> - kvm_stat output
> - trace-cmd record -e kvm; trace-cmd report

Doesn't seem to be part of mainline, are you refering to this trace-cmd?
git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/trace-cmd.git
Comment 4 Török Edwin 2011-05-30 09:25:58 UTC
(In reply to comment #1)
> - qemu monitor
>     (qemu) info registers
>     (qemu) x/40i $eip - 32

Hmm libvirt doesn't provide access to qemu monitor on purpose.
Run it manually like this:
/usr/bin/kvm -S -cpu phenom,+wdt,+skinit,+osvw,+3dnowprefetch,+misalignsse,+sse4a,+abm,+cr8legacy,+extapic,+cmp_legacy,+lahf_lm,+rdtscp,+pdpe1gb,+popcnt,+cx16,+ht,+vme -enable-nesting -enable-kvm -m 3072 -smp 5,sockets=5,cores=1,threads=1 -name debian-enc -uuid 55782a0a-937c-fa7b-8db5-86876d151a08  -rtc base=utc -boot order=c,menu=off -drive file=/var/lib/libvirt/images/debian-enc.img,if=none,id=drive-virtio-disk0,boot=on,format=raw -device virtio-blk-pci,bus=pci.0,addr=0x5,drive=drive-virtio-disk0,id=virtio-disk0 -drive if=none,media=cdrom,id=drive-ide0-1-0,readonly=on,format=raw -device ide-drive,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0   -usb -device usb-tablet,id=input0  -vga cirrus -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x6 -monitor stdio

(qemu) info registers
RAX=ffffffff81ca0ac0 RBX=ffff8800ba5a3d48 RCX=ffffffff81c9b020 RDX=0000000000000000
RSI=00000000000000ff RDI=00000000000000f0 RBP=ffff8800bf003f88 RSP=ffff8800bf003f88
R8 =0000000000000000 R9 =0000000000000001 R10=0000000000000001 R11=00000090ffffff90
R12=0000000000000004 R13=ffff8800ba5a3d6c R14=ffff8800ba5a3d00 R15=ffff8800bf00d1c0
RIP=ffffffff81023f75 RFL=00000046 [---Z-P-] CPL=0 II=0 A20=1 SMM=0 HLT=1
ES =0000 0000000000000000 ffffffff 00000000
CS =0010 0000000000000000 ffffffff 00a09b00 DPL=0 CS64 [-RA]
SS =0018 0000000000000000 ffffffff 00c09300 DPL=0 DS   [-WA]
DS =0000 0000000000000000 ffffffff 00000000
FS =0000 00007fc3a9d4b700 ffffffff 00000000
GS =0000 ffff8800bf000000 ffffffff 00000000
LDT=0000 0000000000000000 0000ffff 00000000
TR =0040 ffff8800bf00e640 00002087 00008b00 DPL=0 TSS64-busy
GDT=     ffff8800bf004000 0000007f
IDT=     ffffffff81dd5000 00000fff
CR0=8005003b CR2=00000000019093dc CR3=00000000bab17000 CR4=000006f0
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
EFER=0000000000000d01
FCW=037f FSW=3800 [ST=7] FTW=80 MXCSR=00001f80
FPR0=8200000000000000 c01d FPR1=0000000000000000 0000
FPR2=0000000000000000 0000 FPR3=0000000000000000 0000
FPR4=0000000000000000 0000 FPR5=0000000000000000 0000
FPR6=0000000000000000 0000 FPR7=0000000000000000 0000
XMM00=00ff0000000000000000000000000000 XMM01=00000000000000000000000000000000
XMM02=ffffffff00000000000000ff00000000 XMM03=ffffffff00000000000000ff00000000
XMM04=776f6e206c6c695700000000019039e0 XMM05=00000000000000000000000000000000
XMM06=00000000000000000000000000000000 XMM07=00000000000000000000000000000000
XMM08=00000000000000000000000000000000 XMM09=00000000000000000000000000000000
XMM10=00000000000000000000000000000000 XMM11=00000000000000000000000000000000
XMM12=00000000000000000000000000000000 XMM13=00000000000000000000000000000000
XMM14=00000000000000000000000000000000 XMM15=00000000000000000000000000000000

(qemu)  x/40i $eip - 32
0xffffffff81023f55:  leaveq 
0xffffffff81023f56:  retq   
0xffffffff81023f57:  nopw   0x0(%rax,%rax,1)
0xffffffff81023f60:  push   %rbp
0xffffffff81023f61:  mov    %rsp,%rbp
0xffffffff81023f64:  sti    
0xffffffff81023f65:  hlt    
0xffffffff81023f66:  leaveq 
0xffffffff81023f67:  retq   
0xffffffff81023f68:  nopl   0x0(%rax,%rax,1)
0xffffffff81023f70:  push   %rbp
0xffffffff81023f71:  mov    %rsp,%rbp
0xffffffff81023f74:  hlt    
0xffffffff81023f75:  leaveq 
0xffffffff81023f76:  retq   
0xffffffff81023f77:  nopw   0x0(%rax,%rax,1)
0xffffffff81023f80:  push   %rbp
0xffffffff81023f81:  mov    %rsp,%rbp
0xffffffff81023f84:  clts   
0xffffffff81023f86:  leaveq 
0xffffffff81023f87:  retq   
0xffffffff81023f88:  nopl   0x0(%rax,%rax,1)
0xffffffff81023f90:  push   %rbp
0xffffffff81023f91:  mov    %rsp,%rbp
0xffffffff81023f94:  mov    %cr0,%rax
0xffffffff81023f97:  leaveq 
0xffffffff81023f98:  retq   
0xffffffff81023f99:  nopl   0x0(%rax)
0xffffffff81023fa0:  push   %rbp
0xffffffff81023fa1:  mov    %rsp,%rbp
0xffffffff81023fa4:  mov    %rdi,%cr0
0xffffffff81023fa7:  leaveq 
0xffffffff81023fa8:  retq   
0xffffffff81023fa9:  nopl   0x0(%rax)
0xffffffff81023fb0:  push   %rbp
0xffffffff81023fb1:  mov    %rsp,%rbp
0xffffffff81023fb4:  mov    %cr2,%rax
0xffffffff81023fb7:  leaveq 
0xffffffff81023fb8:  retq   
0xffffffff81023fb9:  nopl   0x0(%rax)
Comment 5 Avi Kivity 2011-05-30 10:31:43 UTC
On 05/30/2011 12:20 PM, bugzilla-daemon@bugzilla.kernel.org wrote:
> https://bugzilla.kernel.org/show_bug.cgi?id=36222
>
>
>
>
>
> --- Comment #3 from Török Edwin<edwintorok@gmail.com>   2011-05-30 09:20:06
> ---
> Created an attachment (id=60042)
>   -->  (https://bugzilla.kernel.org/attachment.cgi?id=60042)
> trace-cmd record -e kvm; ^C; trace-cmd report
>
> (In reply to comment #1)
> >  Please also post
> >
> >  - kvm_stat output
> >  - trace-cmd record -e kvm; trace-cmd report
>
> Doesn't seem to be part of mainline, are you refering to this trace-cmd?
> git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/trace-cmd.git
>

Yes.  Install udis86 and udis86-devel before building it, please.
Comment 6 Avi Kivity 2011-05-30 10:55:39 UTC
On 05/30/2011 12:26 PM, bugzilla-daemon@bugzilla.kernel.org wrote:
> https://bugzilla.kernel.org/show_bug.cgi?id=36222
>
>
>
>
>
> --- Comment #4 from Török Edwin<edwintorok@gmail.com>   2011-05-30 09:25:58
> ---
> (In reply to comment #1)
> >  - qemu monitor
> >      (qemu) info registers
> >      (qemu) x/40i $eip - 32

> 0xffffffff81023f74:  hlt
> 0xffffffff81023f75:  leaveq
> 0xffffffff81023f76:  retq

Looks like the ordinary idle loop.  What does the guest say while it's 
shutting down?

Seems like some daemon can't stop itself, not a host issue.
Comment 7 Török Edwin 2011-05-30 10:58:47 UTC
It says:
Will now halt.
_
Comment 8 Török Edwin 2011-05-30 11:01:00 UTC
And that corresponds to this script:
	log_action_msg "Will now halt"
	halt -d -f $netdown $poweroff $hddown
Comment 9 Török Edwin 2011-05-30 11:09:45 UTC
Using -serial stdio, and console=ttyS0 I see an Oops when running 'halt -f -p' in the guest:
/[   36.308445] invalid opcode: 0000 [#1] SMP 
[   36.308445] CPU 1 
[   36.308445] Modules linked in:
[   36.308445] 
[   36.308445] Pid: 0, comm: kworker/0:0 Not tainted 3.0.0-rc1 #8 Bochs Bochs
[   36.308445] RIP: 0010:[<ffffffff8101cf19>]  [<ffffffff8101cf19>] native_play_dead+0xd9/0xf0
[   36.308445] RSP: 0018:ffff8800bbeb1ef8  EFLAGS: 00010046
[   36.308445] RAX: ffff8800bbeb0010 RBX: ffff8800bbeb0010 RCX: 0000000000000000
[   36.308445] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8800bbeb1ee4
[   36.308445] RBP: ffff8800bbeb1f08 R08: ffff8800bbeb1edc R09: ffff8800bbeb1ed8
[   36.308445] R10: 0000000874121b10 R11: 0000000000000000 R12: 00000000ffffffff
[   36.308445] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[   36.308445] FS:  00007f0c93b3f700(0000) GS:ffff8800bf100000(0000) knlGS:0000000000000000
[   36.308445] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[   36.308445] CR2: 00007f9c8e7c0f80 CR3: 0000000001c93000 CR4: 00000000000006e0
[   36.308445] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   36.308445] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[   36.308445] Process kworker/0:0 (pid: 0, threadinfo ffff8800bbeb0000, task ffff8800bbe76740)
[   36.308445] Stack:
[   36.308445]  ffff8800bbeb0010 ffffffff81d10810 ffff8800bbeb1f28 ffffffff810018ae
[   36.308445]  0000000000000001 0000000000000000 ffff8800bbeb1f48 ffffffff8162c73b
[   36.308445]  0000000000000000 0000000000000000 0000000000000000 0000000000000000
[   36.308445] Call Trace:
[   36.308445]  [<ffffffff810018ae>] cpu_idle+0x9e/0xb0
[   36.308445]  [<ffffffff8162c73b>] start_secondary+0x177/0x17c
[   36.308445] Code: 09 f4 65 48 8b 1c 25 c8 b5 00 00 48 81 eb c8 1f 00 00 0f 09 66 66 90 66 90 31 c9 0f 1f 80 00 00 00 00 0f ae 3b 48 89 d8 48 89 ca <0f> 01 c8 0f ae f0 4c 89 e0 0f 01 c9 eb e9 66 0f 1f 84 00 00 00 
[   36.308445] RIP  [<ffffffff8101cf19>] native_play_dead+0xd9/0xf0
[   36.308445]  RSP <ffff8800bbeb1ef8>
[   36.308445] ---[ end trace b72c6a73fe4299e2 ]---
[   36.330393] invalid opcode: 0000 [#2] SMP 
[   36.330393] CPU 2 
[   36.330393] Modules linked in:
[   36.330393] 
[   36.330393] Pid: 0, comm: kworker/0:1 Tainted: G      D     3.0.0-rc1 #8 Bochs Bochs
[   36.330393] RIP: 0010:[<ffffffff8101cf19>]  [<ffffffff8101cf19>] native_play_dead+0xd9/0xf0
[   36.330393] RSP: 0018:ffff8800bbecfef8  EFLAGS: 00010046
[   36.330393] RAX: ffff8800bbece010 RBX: ffff8800bbece010 RCX: 0000000000000000
[   36.330393] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8800bbecfee4
[   36.330393] RBP: ffff8800bbecff08 R08: ffff8800bbecfedc R09: ffff8800bbecfed8
[   36.330393] R10: 000000166d13e921 R11: 0000000000000000 R12: 00000000ffffffff
[   36.330393] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[   36.330393] FS:  00007ff8f51e97a0(0000) GS:ffff8800bf200000(0000) knlGS:0000000000000000
[   36.330393] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[   36.330393] CR2: 00007ff8f4aa7920 CR3: 0000000001c93000 CR4: 00000000000006e0
[   36.330393] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   36.330393] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[   36.330393] Process kworker/0:1 (pid: 0, threadinfo ffff8800bbece000, task ffff8800bbec0ec0)
[   36.330393] Stack:
[   36.330393]  ffff8800bbece010 ffffffff81d10810 ffff8800bbecff28 ffffffff810018ae
[   36.330393]  0000000000000002 0000000000000000 ffff8800bbecff48 ffffffff8162c73b
[   36.330393]  0000000000000000 0000000000000000 0000000000000000 0000000000000000
[   36.330393] Call Trace:
[   36.330393]  [<ffffffff810018ae>] cpu_idle+0x9e/0xb0
[   36.330393]  [<ffffffff8162c73b>] start_secondary+0x177/0x17c
[   36.330393] Code: 09 f4 65 48 8b 1c 25 c8 b5 00 00 48 81 eb c8 1f 00 00 0f 09 66 66 90 66 90 31 c9 0f 1f 80 00 00 00 00 0f ae 3b 48 89 d8 48 89 ca <0f> 01 c8 0f ae f0 4c 89 e0 0f 01 c9 eb e9 66 0f 1f 84 00 00 00 
[   36.330393] RIP  [<ffffffff8101cf19>] native_play_dead+0xd9/0xf0
[   36.330393]  RSP <ffff8800bbecfef8>
[   36.330393] ---[ end trace b72c6a73fe4299e3 ]---
[   36.330393] Kernel panic - not syncing: Attempted to kill the idle task!
[   36.330393] Pid: 0, comm: kworker/0:1 Tainted: G      D     3.0.0-rc1 #8
[   36.330393] Call Trace:
[   36.330393]  [<ffffffff81630721>] panic+0x8c/0x190
[   36.330393]  [<ffffffff8104d033>] do_exit+0x6a3/0x8a0
[   36.330393]  [<ffffffff81049544>] ? kmsg_dump+0x44/0x100
[   36.330393]  [<ffffffff81005633>] oops_end+0x83/0xb0
[   36.330393]  [<ffffffff81005766>] die+0x56/0x90
[   36.330393]  [<ffffffff81002bcc>] do_trap+0xbc/0x160
[   36.330393]  [<ffffffff810030c0>] do_invalid_op+0x90/0xb0
[   36.330393]  [<ffffffff8101cf19>] ? native_play_dead+0xd9/0xf0
[   36.330393]  [<ffffffff8103a97b>] ? __dequeue_entity+0x2b/0x50
[   36.330393]  [<ffffffff81024c48>] ? pvclock_clocksource_read+0x58/0xd0
[   36.330393]  [<ffffffff8126f0c5>] ? timerqueue_del+0x35/0x90
[   36.330393]  [<ffffffff8106d396>] ? __remove_hrtimer+0x36/0xa0
[   36.330393]  [<ffffffff81634d5b>] invalid_op+0x1b/0x20
[   36.330393]  [<ffffffff8101cf19>] ? native_play_dead+0xd9/0xf0
[   36.330393]  [<ffffffff8101cec5>] ? native_play_dead+0x85/0xf0
[   36.330393]  [<ffffffff810018ae>] cpu_idle+0x9e/0xb0
[   36.330393]  [<ffffffff8162c73b>] start_secondary+0x177/0x17c
[   36.308445] Kernel panic - not syncing: Attempted to kill the idle task!
[   36.308445] Pid: 0, comm: kworker/0:0 Tainted: G      D     3.0.0-rc1 #8
[   36.308445] Call Trace:
[   36.308445]  [<ffffffff81630721>] panic+0x8c/0x190
[   36.308445]  [<ffffffff8104d033>] do_exit+0x6a3/0x8a0
[   36.308445]  [<ffffffff81049544>] ? kmsg_dump+0x44/0x100
[   36.308445]  [<ffffffff81005633>] oops_end+0x83/0xb0
[   36.308445]  [<ffffffff81005766>] die+0x56/0x90
[   36.308445]  [<ffffffff81002bcc>] do_trap+0xbc/0x160
[   36.308445]  [<ffffffff810030c0>] do_invalid_op+0x90/0xb0
[   36.308445]  [<ffffffff8101cf19>] ? native_play_dead+0xd9/0xf0
[   36.308445]  [<ffffffff81024c48>] ? pvclock_clocksource_read+0x58/0xd0
[   36.308445]  [<ffffffff8126f0c5>] ? timerqueue_del+0x35/0x90
[   36.308445]  [<ffffffff8106d396>] ? __remove_hrtimer+0x36/0xa0
[   36.308445]  [<ffffffff81634d5b>] invalid_op+0x1b/0x20
[   36.308445]  [<ffffffff8101cf19>] ? native_play_dead+0xd9/0xf0
[   36.308445]  [<ffffffff8101cec5>] ? native_play_dead+0x85/0xf0
[   36.308445]  [<ffffffff810018ae>] cpu_idle+0x9e/0xb0
Comment 10 Avi Kivity 2011-05-30 11:38:09 UTC
On 05/30/2011 02:09 PM, bugzilla-daemon@bugzilla.kernel.org wrote:
> [   36.308445]  [<ffffffff810018ae>] cpu_idle+0x9e/0xb0
> [   36.308445]  [<ffffffff8162c73b>] start_secondary+0x177/0x17c
> [   36.308445] Code: 09 f4 65 48 8b 1c 25 c8 b5 00 00 48 81 eb c8 1f 00 00 0f
> 09 66 66 90 66 90 31 c9 0f 1f 80 00 00 00 00 0f ae 3b 48 89 d8 48 89 ca<0f> 
> 01
> c8 0f ae f0 4c 89 e0 0f 01 c9 eb e9 66 0f 1f 84 00 00 00

0f 01 c8                 monitor %rax,%rcx,%rdx

The guest thinks it has monitor/mwait, which kvm doesn't emulate.

What's the guest's /proc/cpuinfo?
Comment 11 Török Edwin 2011-05-30 11:43:37 UTC
With 3.0.0-rc1:
processor       : 4
vendor_id       : AuthenticAMD
cpu family      : 16
model           : 2
model name      : AMD Phenom(tm) 9550 Quad-Core Processor
stepping        : 3
cpu MHz         : 3214.320
cache size      : 512 KB
fpu             : yes
fpu_exception   : yes
cpuid level     : 5
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx mmxext fxsr_opt pdpe1gb lm rep_good nopl extd_apicid pni cx16 popcnt hypervisor lahf_lm cmp_legacy svm cr8_legacy abm sse4a misalignsse 3dnowprefetch npt
bogomips        : 6428.64
TLB size        : 1024 4K pages
clflush size    : 64
cache_alignment : 64
address sizes   : 40 bits physical, 48 bits virtual
power management:

With 2.6.39 (which shuts down properly) it is the same.
Comment 12 Török Edwin 2011-05-30 12:26:19 UTC
Bisection tells me this is the offending commit (see below), but I see you found it too.

commit 349c004e3d31fda23ad225b61861be38047fff16
Author: Christoph Lameter <cl@linux.com>
Date:   Sat Mar 12 12:50:10 2011 +0100

    x86: A fast way to check capabilities of the current cpu
    
    Add this_cpu_has() which determines if the current cpu has a certain
    ability using a segment prefix and a bit test operation.
    
    For that we need to add bit operations to x86s percpu.h.
    
    Many uses of cpu_has use a pointer passed to a function to determine
    the current flags. That is no longer necessary after this patch.
    
    However, this patch only converts the straightforward cases where
    cpu_has is used with this_cpu_ptr. The rest is work for later.
    
    -tj: Rolled up patch to add x86_ prefix and use percpu_read() instead
         of percpu_read_stable().
    
    Signed-off-by: Christoph Lameter <cl@linux.com>
    Acked-by: Tejun Heo <tj@kernel.org>
    Signed-off-by: Tejun Heo <tj@kernel.org>
Comment 13 Florian Mickler 2011-06-06 10:57:48 UTC
A patch referencing this bug report has been merged in v3.0-rc2:

commit 4f3c125c7420c85eaff627145557e392a871922d
Author: Avi Kivity <avi@redhat.com>
Date:   Mon May 30 08:23:57 2011 -0400

    x86: Fix mwait_play_dead() faulting on mwait-incapable cpus