linux-kernel - Re: kvm: unable to handle kernel NULL pointer dereference

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Date:	Thu, 5 Jun 2008 08:09:32 +0200
From:	Tobias Diedrich <ranma+kernel@...edrich.de>
To:	Chris Wright <chrisw@...s-sol.org>
Cc:	Avi Kivity <avi@...ranet.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: kvm: unable to handle kernel NULL pointer dereference

Chris Wright wrote:
> * Tobias Diedrich (ranma+kernel@...edrich.de) wrote:
> > BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
> > IP: [<ffffffff8021d44f>] svm_vcpu_run+0x34/0x351
> > PGD 7e01b067 PUD 7bc86067 PMD 0 
> > Oops: 0000 [1] PREEMPT 
> > CPU 0 
> > Modules linked in: zaurus cdc_ether usbnet snd_hda_intel k8temp radeon drm snd_emu10k1_synth snd_emux_synth snd_seq_virmidi snd_seq_midi_emul snd_emu10k1 snd_seq_midi snd_rawmidi snd_ac97_codec ac97_bus snd_util_mem forcedeth emu10k1_gp gameport snd_hwdep pata_amd [last unloaded: snd_hda_intel]
> > Pid: 11113, comm: kvm Tainted: G        W 2.6.26-rc4 #29
> > RIP: 0010:[<ffffffff8021d44f>]  [<ffffffff8021d44f>] svm_vcpu_run+0x34/0x351
> > RSP: 0018:ffff81007866fc38  EFLAGS: 00010046
> > RAX: ffff810076d42040 RBX: 00000000fffffffc RCX: 0000000000000000
> > RDX: ffff810076d42040 RSI: ffff810079b41000 RDI: ffff810076d42040
> > RBP: ffff81007866fc88 R08: 0000000000000002 R09: 0000000000000001
> > R10: ffffffff804237e5 R11: ffff81007866fc88 R12: ffff810076d42040
> > R13: 0000000000000000 R14: ffff810079b41000 R15: 000000000000ae80
> > FS:  00000000419b1950(0063) GS:ffffffff808bc000(0000) knlGS:00000000f712b6c0
> > CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> > CR2: 0000000000000008 CR3: 0000000079b8d000 CR4: 00000000000006e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> > Process kvm (pid: 11113, threadinfo ffff81007866e000, task ffff810019db8300)
> > Stack:  ffff81007866fc68 ffff810076d42040 ffff810076d42040 ffff81007bc600a8
> >  ffff810076d42040 00000000fffffffc ffff810076d42040 0000000000000000
> >  ffff810079b41000 000000000000ae80 ffff81007866fcc8 ffffffff8020fa41
> > Call Trace:
> >  [<ffffffff8020fa41>] kvm_arch_vcpu_ioctl_run+0x46a/0x6df
> >  [<ffffffff8020ab98>] kvm_vcpu_ioctl+0xfd/0x3d0
> >  [<ffffffff80293df1>] ? kmem_cache_free+0x6e/0x81
> >  [<ffffffff8024cf89>] ? __dequeue_signal+0x1c/0x167
> >  [<ffffffff802a322e>] vfs_ioctl+0x2a/0x77
> >  [<ffffffff802a34d6>] do_vfs_ioctl+0x25b/0x270
> >  [<ffffffff802a352d>] sys_ioctl+0x42/0x65
> >  [<ffffffff8021fffb>] system_call_after_swapgs+0x7b/0x80
> > 
> > Code: 55 41 54 53 48 83 ec 28 48 89 7d b8 48 8b 87 50 15 00 00 48 8b 0d ba 9c 6f 00 c6 40 5c 00 48 8b 45 b8 83 b8 a0 00 00 00 00 75 0d <48> 8b 51 08 48 39 90 68 15 00 00 74 4f 8b 41 14 3b 41 10 76 1a 
> > RIP  [<ffffffff8021d44f>] svm_vcpu_run+0x34/0x351
> 
> Odd, svm_data is NULL, so svm_data->asid_generation is oopsing.
> 
>   static void pre_svm_run(struct vcpu_svm *svm)
>   {
>   	int cpu = raw_smp_processor_id();
>   
>   	struct svm_cpu_data *svm_data = per_cpu(svm_data, cpu);
>   
>   	svm->vmcb->control.tlb_ctl = TLB_CONTROL_DO_NOTHING;
>   	if (svm->vcpu.cpu != cpu ||
>   	    svm->asid_generation != svm_data->asid_generation) <--- here <---
>   		new_asid(svm, svm_data);
>   }
> 
> Doesn't really make any sense to find svm_data == NULL, since it's
> allocated during module init (or boot in this case).  If that allocation
> failed, you shouldn't ever get as far as vcpu_run.
> 
> I'm assuming that:
> gdb -q vmlinux
> (gdb) p/x 0xffffffff8021d456 + 0x6f9cba
> is the same as
> (gdb) p/x &per_cpu__svm_data

Almost:
ranma@...chior:~/src/linux-2.6.26-rc4.forcedwol$ gdb -q vmlinux
Using host libthread_db library "/lib/libthread_db.so.1".
(gdb)  p/x 0xffffffff8021d456 + 0x6f9cba
$1 = 0xffffffff80917110
(gdb) p/x &per_cpu__svm_data
$2 = 0xffffffff809170f8
(gdb) 

> Otherwise, seems a bit like memory corruption (doesn't happen here w/
> your .config).

HTH,

-- 
Tobias						PGP: http://9ac7e0bc.uguu.de
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