WARN_ON in kvm_queue_exception_e triggers

Jan Kiszka
2008-04-28T17:35:10Z

Hi,

sorry, the test environment is not really reproducible (stock kvm-66,
yet unpublished NMI support by Sheng Yang and me, special guest), but
I'm just fishing for some ideas on what may cause the flood of the
following warning in my kernel log:

------------[ cut here ]------------
WARNING: at /data/kvm-66/kernel/x86.c:180
kvm_queue_exception_e+0x30/0x54 [kvm]()
Modules linked in: ipt_MASQUERADE kvm_intel kvm bridge tun ip6t_LOG
nf_conntrack_ipv6 xt_pkttype ipt_LOG xt_limit snd_pcm_oss snd_mixer_oss
snd_seq snd_seq_device nls_utf8 cifs af_packet ip6t_REJECT xt_tcpudp
ipt_REJECT xt_state iptable_mangle iptable_nat nf_nat iptable_filter
ip6table_mangle nf_conntrack_ipv4 nf_conntrack ip_tables ip6table_filter
ip6_tables cpufreq_conservative x_tables cpufreq_userspace
cpufreq_powersave acpi_cpufreq ipv6 microcode fuse ohci_hcd loop rfcomm
l2cap wlan_scan_sta ath_rate_sample ath_pci snd_hda_intel wlan pcmcia
firmware_class hci_usb snd_pcm snd_timer ath_hal(P) sdhci battery
bluetooth button ohci1394 mmc_core rtc_cmos parport_pc intel_agp
rtc_core dock ac snd_page_alloc iTCO_wdt ieee1394 sky2 rtc_lib
yenta_socket parport snd_hwdep snd iTCO_vendor_support i2c_i801
rsrc_nonstatic pcmcia_core sg i2c_core soundcore serio_raw joydev
sha256_generic aes_x86_64 aes_generic cbc dm_crypt crypto_blkcipher
usbhid hid ff_memless sd_mod ehci_hcd uhci_hcd usbcore dm_snapshot
dm_mod edd ext3 mbcache jbd fan ata_piix ahci libata scsi_mod thermal
processor
Pid: 4718, comm: qemu-system-x86 Tainted: P N
2.6.25-rc5-git2-109.8-default #1

Call Trace:
[<ffffffff8020d826>] dump_trace+0xc4/0x576
[<ffffffff8020dd18>] show_trace+0x40/0x57
[<ffffffff8044e341>] _etext+0x72/0x7b
[<ffffffff80238137>] warn_on_slowpath+0x58/0x80
[<ffffffff886e2e05>] :kvm:kvm_queue_exception_e+0x30/0x54
[<ffffffff886e3678>] :kvm:kvm_task_switch+0xca/0x20a
[<ffffffff8870d096>] :kvm_intel:handle_task_switch+0x19/0x1b
[<ffffffff8870cb1b>] :kvm_intel:kvm_handle_exit+0x7f/0x9c
[<ffffffff886e51e2>] :kvm:kvm_arch_vcpu_ioctl_run+0x49b/0x686
[<ffffffff886e08c9>] :kvm:kvm_vcpu_ioctl+0xf7/0x3ca
[<ffffffff802ad0ba>] vfs_ioctl+0x2a/0x78
[<ffffffff802ad34f>] do_vfs_ioctl+0x247/0x261
[<ffffffff802ad3be>] sys_ioctl+0x55/0x77
[<ffffffff8020c18a>] system_call_after_swapgs+0x8a/0x8f
[<00007faed2969267>]

---[ end trace 5d286714f3c5c50f ]---

I'm suspecting that it is the way our guest raises a triple fault in
order to initiate a restart. At least it tells us via virtual console
that it wants to restart, and those messages start around the same time.
So, while waiting for my colleagues to dig out the precise triple-fault
code pattern (for a cleaner test case), maybe someone could comment on
potential reasons for this warning - or even ways to resolve them.

Thanks!