Re: kernel BUG at arch/x86/kernel/traps.c:643! when run Redhat7(v3.10) in kvm guest

[Andy Lutomirski]

On Thu, Oct 13, 2016 at 11:14 PM, Kefeng Wang
<wangkefeng.wang@xxxxxxxxxx> 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 <luto@xxxxxxxxxx>
> 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

>
> Thanks,
> Kefeng
>
> [1] BUG_ON
> ----------------------------------------------------
> [347134.486436] ------------[ cut here ]------------
> [347134.487310] kernel BUG at arch/x86/kernel/traps.c:643!
> [347134.487398] invalid opcode: 0000 [#1] SMP
> [347134.500532] Modules linked in:loop binfmt_misc nf_log_ipv4 nf_log_common xt_LOG softdog ipmi_devintf ipmi_msghandler xfs libcrc32c tipc squashfs ipt_REJECT iptable_filter ip_tables dm_mod crct10dif_pclmul crct10dif_common crc32_pclmul crc32c_intel ghash_clmulni_intel aesni_intel lrw ppdev gf128mul i2c_piix4 glue_helper ablk_helper i2c_core cryptd serio_raw parport_pc parport pcspkr ext3 mbcache jbd ata_generic pata_acpi virtio_console(OVE) virtio_blk(OVE) virtio_balloon(OVE) virtio_net(OVE) ata_piix libata floppy virtio_pci(OVE) virtio_ring(OVE) virtio(OVE)
> [347134.525182] CPU: 5 PID: 0 Comm: swapper/5 Tainted: G           O E ----V-------   3.10.0-229.20.1.x86_64 #1 SMP Mon Apr 18 11:26:55 UTC 2016
> [347134.525182] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.1-0-g4adadbd-20160318_175052-HGH1000008214 04/01/2014
> [347134.525182] task: ffff8803fa2c5c00 ti: ffff8803fa2ec000 task.ti: ffff8803fa2ec000
> [347134.525182] RIP: 0010:[<ffffffff8160fb13>]  [<ffffffff8160fb13>] do_device_not_available+0x13/0x60
> [347134.525182] RSP: 0018:ffff8803fa2abc80  EFLAGS: 00010046
> [347134.525182] RAX: 000000008160ecec RBX: 0000000000000000 RCX: ffffffff8160ecec
> [347134.525182] RDX: 00000000ffffffff RSI: 0000000000000000 RDI: ffff8803fa2abc98
> [347134.525182] RBP: ffff8803fa2abc88 R08: 0000000000000000 R09: 0000000000000000
> [347134.525182] R10: 0000000000000001 R11: 0000000000000005 R12: ffff8803fa2c5c00
> [347134.525182] R13: ffff88040f550a40 R14: ffff8803fa2c6298 R15: 0000000000000005
> [347134.544262] FS:  0000000000000000(0000) GS:ffff88040f540000(0000) knlGS:0000000000000000
> [347134.544262] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> [347134.544262] CR2: 00007f15a4ac0e30 CR3: 00000003f5081000 CR4: 00000000000407e0
> [347134.544262] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [347134.544262] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> [347134.544262] Stack:
> [347134.544262]  0000000000000001 ffff8803fa2abd88 ffffffff81618d8e 0000000000000005
> [347134.544262]  ffff8803fa2c6298 ffff88040f550a40 ffff8803fa2c5c00 ffff8803fa2abd88
> [347134.544262]  ffff8803fa284500 0000000000000005 0000000000000001 0000000000000000
> [347134.544262] Call Trace:
> [347134.544262] Code: 81 a4 24 90 00 00 00 ff fe ff ff e9 df fe ff ff e8 c3 f5 a5 ff 0f 1f 00 66 66 66 66 90 55 48 89 e5 53 66 66 66 66 90 31 db 66 90 <0f> 0b 0f 1f 00 65 8b 1c 25 74 f1 00 00 e8 fb 86 b4 ff eb ea 66
> [347134.544262] RIP  [<ffffffff8160fb13>] do_device_not_available+0x13/0x60
> [347134.544262]  RSP <ffff8803fa2abc80>
> [347134.580457] ---[ end trace 7c0ed2be7ded5c73 ]---
> [347134.580457] Kernel panic - not syncing: Fatal exception
> [347134.580457] Shutting down cpus with NMI
>
>
>
> [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:
>



-- 
Andy Lutomirski
AMA Capital Management, LLC