Re: WARN_ON in kvm_queue_exception_e triggers

Joerg Roedel
2008-04-28T20:37:02Z

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On Mon, Apr 28, 2008 at 07:35:10PM +0200, Jan Kiszka wrote:
> 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 yet unpublished NMI support by Sheng Yang and me, special guest), but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 ]---

Hmm, seems we have to check for DF and triple faults in the
kvm_queue_exception functions too. Does the attached patch fix the
problem (patch is against kvm-66).

Joerg

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diff --git a/kernel/x86.c b/kernel/x86.c
index ef2aba9..a4da0e8 100644
--- a/kernel/x86.c
+++ b/kernel/x86.c
@@ -144,9 +144,23 @@ void kvm_set_apic_base(struct kvm_vcpu *vcpu, u64 data)
}
EXPORT_SYMBOL_GPL(kvm_set_apic_base);

+static void handle_multiple_faults(struct kvm_vcpu *vcpu)
+{
+ if (vcpu->arch.exception.nr != DF_VECTOR) {
+ printk(KERN_DEBUG "kvm: inject_page_fault:"
+ " double fault\n");
+ vcpu->arch.exception.nr = DF_VECTOR;
+ vcpu->arch.exception.error_code = 0;
+ } else
+ set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests);
+}
+
void kvm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr)
{
- WARN_ON(vcpu->arch.exception.pending);
+ if (vcpu->arch.exception.pending) {
+ handle_multiple_faults(vcpu);
+ return;
+ }
vcpu->arch.exception.pending = true;
vcpu->arch.exception.has_error_code = false;
vcpu->arch.exception.nr = nr;
@@ -157,25 +171,16 @@ void kvm_inject_page_fault(struct kvm_vcpu *vcpu, unsigned long addr,
u32 error_code)
{
++vcpu->stat.pf_guest;
- if (vcpu->arch.exception.pending) {
- if (vcpu->arch.exception.nr == PF_VECTOR) {
- printk(KERN_DEBUG "kvm: inject_page_fault:"
- " double fault 0x%lx\n", addr);
- vcpu->arch.exception.nr = DF_VECTOR;
- vcpu->arch.exception.error_code = 0;
- } else if (vcpu->arch.exception.nr == DF_VECTOR) {
- /* triple fault -> shutdown */
- set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests);
- }
- return;
- }
vcpu->arch.cr2 = addr;
kvm_queue_exception_e(vcpu, PF_VECTOR, error_code);
}

void kvm_queue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32 error_code)
{
- WARN_ON(vcpu->arch.exception.pending);
+ if (vcpu->arch.exception.pending) {
+ handle_multiple_faults(vcpu);
+ return;
+ }
vcpu->arch.exception.pending = true;
vcpu->arch.exception.has_error_code = true;
vcpu->arch.exception.nr = nr;

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