On 2016/10/15 2:36, Andy Lutomirski wrote:
> On Thu, Oct 13, 2016 at 11:14 PM, Kefeng Wang
> <wangkefeng.w...@huawei.com> wrote:
>> Hi all,
>>
>> We met BUG_ON in do_device_not_available(fpu exception handler) when run 
>> redhat7 in kvm guest,
>> and there is no special test on this guest, only some network packet receipt 
>> and transmission.
>>
>> I checked the new kernel version, found this commit 
>> 4ecd16ec7059390b430af34bd8bc3ca2b5dcef9a
>> Author: Andy Lutomirski <l...@kernel.org>
>> Date:   Sun Jan 24 14:38:06 2016 -0800
>>
>>     x86/fpu: Fix math emulation in eager fpu mode
>>
>>     Systems without an FPU are generally old and therefore use lazy FPU
>>     switching. Unsurprisingly, math emulation in eager FPU mode is a
>>     bit buggy. Fix it.
>>
>>     There were two bugs involving kernel code trying to use the FPU
>>     registers in eager mode even if they didn't exist and one BUG_ON()
>>     that was incorrect.
>>
>>
>> The BUG_ON() is incorrect, but I have no idea about eager fpu, why the 
>> BUG_ON is incorrect?
>> Should we backport the patch to v3.10, or is there some bugs in the qemu-kvm?
>> Any reply will be appreciated.
> 
> The BUG_ON was incorrect because you could hit it if FPU emulation was
> enabled.  But, unless you explicitly set the "eagerfpu=" option or you
> have some really weird set of cpu flags, old kernels shouldn't have
> hit it.  Is the cpuinfo you pasted below from the guest?  Also, could
> you attach whatever dmesg has to say about FPU in a crashing guest?
> 
> --Andy
> 

Hi Andy and Rik, thanks for your quick response.

Attach more information, and we have no special configuration for fpu, and only 
met this issue once(can't reproduce).


1) cmdline

BOOT_IMAGE=/vmlinuz-3.10.0-229.20.1.x86_64 root=/dev/vda2 oops=panic 
softlockup_panic=1 net.ifnames=0 biosdevname=0 nmi_watchdog=1 selinux=0 
console=tty0 panic=3


2) virsh dumpxml 3 (only cpu parts)
-----------------------
 <memory unit='KiB'>16000000</memory>
  <currentMemory unit='KiB'>16000000</currentMemory>
  <vcpu placement='static'>8</vcpu>
  <resource>
    <partition>/machine</partition>
  </resource>
  <os>
    <type arch='x86_64' machine='pc-i440fx-2.3'>hvm</type>
    <boot dev='cdrom'/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <pae/>
  </features>
  <cpu mode='host-passthrough'>
    <topology sockets='1' cores='8' threads='1'/>
  </cpu>
-----------------------

3) The host os cpuinfo
-----------------------
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 45
model name      : Intel(R) Xeon(R) CPU E5-2690 0 @ 2.90GHz
stepping        : 7
microcode       : 1808
cpu MHz         : 2899.894
cache size      : 20480 KB
physical id     : 0
siblings        : 16
core id         : 0
cpu cores       : 8
apicid          : 0
initial apicid  : 0
fpu             : yes
fpu_exception   : yes
cpuid level     : 13
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov 
pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb 
rdtscp lm constant_tsc arch_perfmon pebs bts rep_good
 nopl xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx 
smx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic popcnt 
tsc_deadline_timer aes xsave avx lahf_lm arat epb xsaveopt pl
n pts dtherm tpr_shadow vnmi flexpriority ept vpid
bogomips        : 5799.78
clflush size    : 64
cache_alignment : 64
address sizes   : 46 bits physical, 48 bits virtual
power management:




4) The guest os cpuinfo

>> [2] The /proc/cpuinfo shows below(show only the first cpu0),
>> --------------------------------
>> localhost:~ # cat /proc/cpuinfo
>> processor       : 0
>> vendor_id       : GenuineIntel
>> cpu family      : 6
>> model           : 45
>> model name      : Intel(R) Xeon(R) CPU E5-2690 0 @ 2.90GHz
>> stepping        : 7
>> microcode       : 0x1
>> cpu MHz         : 2899.992
>> cache size      : 4096 KB
>> physical id     : 0
>> siblings        : 8
>> core id         : 0
>> cpu cores       : 8
>> apicid          : 0
>> initial apicid  : 0
>> fpu             : yes
>> fpu_exception   : yes
>> cpuid level     : 13
>> 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 ss ht syscall nx pdpe1gb rdtscp lm 
>> constant_tsc arch_perfmon rep_good nopl eagerfpu pni pclmulqdq ssse3 cx16 
>> pcid sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx hypervisor 
>> lahf_lm xsaveopt
>> bogomips        : 5799.98
>> clflush size    : 64
>> cache_alignment : 64
>> address sizes   : 42 bits physical, 48 bits virtual
>> power management:
>>
> 

5) parts of bootmsg


 [    0.000000] Booting paravirtualized kernel on KVM
 [    0.000000] setup_percpu: NR_CPUS:5120 nr_cpumask_bits:8 nr_cpu_ids:8 
nr_node_ids:1
 [    0.000000] PERCPU: Embedded 28 pages/cpu @ffff88040f400000 s82816 r8192 
d23680 u262144
 [    0.000000] KVM setup async PF for cpu 0
 [    0.000000] Built 1 zonelists in Zone order, mobility grouping on.  Total 
pages: 3933317
 [    0.000000] Policy zone: Normal
 [    0.000000] Kernel command line: BOOT_IMAGE=/vmlinuz-3.10.0-229.20.1.x86_64 
root=/dev/vda2 oops=panic softlockup_panic=1 net.ifnames=0 biosdevname=0 
nmi_watchdog=1 selinux=0 console=tty0 panic=3
 [    0.000000] PID hash table entries: 4096 (order: 3, 32768 bytes)
 [    0.000000] xsave: enabled xstate_bv 0x7, cntxt size 0x340
 [    0.000000] Checking aperture...
 [    0.000000] No AGP bridge found
 [    0.000000] Memory: 15375712k/17032192k available (6255k kernel code, 
1049096k absent, 607384k reserved, 4184k data, 1604k init)
 [    0.000000] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=8, Nodes=1
 [    0.000000] Hierarchical RCU implementation.
 [    0.000000]         RCU restricting CPUs from NR_CPUS=5120 to nr_cpu_ids=8.
 [    0.000000]         Experimental no-CBs for all CPUs
 [    0.000000]         Experimental no-CBs CPUs: 0-7.
 [    0.000000] NR_IRQS:327936 nr_irqs:744 16
 [    0.000000] Console: colour VGA+ 80x25
 [    0.000000] console [tty0] enabled
 [    0.000000] allocated 63963136 bytes of page_cgroup
 [    0.000000] please try 'cgroup_disable=memory' option if you don't want 
memory cgroups
 [    0.000000] tsc: Detected 2899.992 MHz processor
 [    0.002000] Calibrating delay loop (skipped) preset value.. 5799.98 
BogoMIPS (lpj=2899992)
 [    0.002006] pid_max: default: 32768 minimum: 301
 [    0.003029] Security Framework initialized
 [    0.003584] SELinux:  Disabled at boot.
 [    0.005623] Dentry cache hash table entries: 2097152 (order: 12, 16777216 
bytes)
 [    0.009697] Inode-cache hash table entries: 1048576 (order: 11, 8388608 
bytes)
 [    0.011961] Mount-cache hash table entries: 4096
 [    0.012178] Initializing cgroup subsys memory
 [    0.013011] Initializing cgroup subsys devices
 [    0.013573] Initializing cgroup subsys freezer
 [    0.014004] Initializing cgroup subsys net_cls
 [    0.015003] Initializing cgroup subsys blkio
 [    0.015558] Initializing cgroup subsys perf_event
 [    0.016007] Initializing cgroup subsys hugetlb
 [    0.016637] CPU: Physical Processor ID: 0
 [    0.017003] CPU: Processor Core ID: 0
 [    0.018004] mce: CPU supports 10 MCE banks
 [    0.018597] Last level iTLB entries: 4KB 0, 2MB 0, 4MB 0
                 Last level dTLB entries: 4KB 0, 2MB 0, 4MB 0
                 tlb_flushall_shift: 6
 [    0.019169] Freeing SMP alternatives: 24k freed
 [    0.023150] ACPI: Core revision 20130517
 [    0.024384] ACPI: All ACPI Tables successfully acquired
 [    0.025016] ftrace: allocating 23959 entries in 94 pages
 [    0.031284] Enabling x2apic
 [    0.031884] Enabled x2apic
 [    0.032004] Switched APIC routing to physical x2apic.
 [    0.033629] ..TIMER: vector=0x30 apic1=0 pin1=2 apic2=-1 pin2=-1
 [    0.034002] smpboot: CPU0: Intel(R) Xeon(R) CPU E5-2690 0 @ 2.90GHz (fam: 
06, model: 2d, step
 [    0.035052] Performance Events: 16-deep LBR, SandyBridge events, Intel PMU 
driver.
 [    0.037935] perf_event_intel: PEBS disabled due to CPU errata, please 
upgrade microcode
 [    0.038005] ... version:                2
 [    0.038544] ... bit width:              48
 [    0.039003] ... generic registers:      4
 [    0.039546] ... value mask:             0000ffffffffffff
 [    0.040003] ... max period:             000000007fffffff
 [    0.040565] ... fixed-purpose events:   3
 [    0.041002] ... event mask:             000000070000000f
 [    0.042819] NMI watchdog: enabled on all CPUs, permanently consumes one 
hw-PMU counter.
 [    0.042791] kvm-clock: cpu 1, msr 4:f889041, secondary cpu clock
 [    0.055016] KVM setup async PF for cpu 1
 [    0.055025] kvm-clock: cpu 2, msr 4:f889081, secondary cpu clock
 [    0.067015] KVM setup async PF for cpu 2
 [    0.067022] kvm-clock: cpu 3, msr 4:f8890c1, secondary cpu clock
 [    0.079015] KVM setup async PF for cpu 3
 [    0.079023] kvm-clock: cpu 4, msr 4:f889101, secondary cpu clock
 [    0.091013] KVM setup async PF for cpu 4
 [    0.091019] kvm-clock: cpu 5, msr 4:f889141, secondary cpu clock
 [    0.103014] KVM setup async PF for cpu 5
 [    0.103021] kvm-clock: cpu 6, msr 4:f889181, secondary cpu clock
 [    0.115014] KVM setup async PF for cpu 6
 [    0.043097] smpboot: Booting Node   0, Processors  #1 #2 #3 #4 #5 #6 #7 OK
 [    0.115021] kvm-clock: cpu 7, msr 4:f8891c1, secondary cpu clock
 [    0.127022] Brought up 8 CPUs
 [    0.127015] KVM setup async PF for cpu 7
 [    0.128005] smpboot: Total of 8 processors activated (46399.87 BogoMIPS)
 [    0.129202] devtmpfs: initialized


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