On 2014-06-29 12:24, Gleb Natapov wrote: > On Sun, Jun 29, 2014 at 11:56:03AM +0200, Jan Kiszka wrote: >> On 2014-06-29 08:46, Gleb Natapov wrote: >>> On Sat, Jun 28, 2014 at 01:44:31PM +0200, Borislav Petkov wrote: >>>> qemu-system-x86-20240 [006] ...1 9406.484134: kvm_page_fault: address 7fffb62ba318 error_code 2 >>>> qemu-system-x86-20240 [006] ...1 9406.484136: kvm_inj_exception: #PF (0x2)a >>>> >>>> kvm injects the #PF into the guest. >>>> >>>> qemu-system-x86-20240 [006] d..2 9406.484136: kvm_entry: vcpu 1 >>>> qemu-system-x86-20240 [006] d..2 9406.484137: kvm_exit: reason PF excp rip 0xffffffff8161130f info 2 7fffb62ba318 >>>> qemu-system-x86-20240 [006] ...1 9406.484138: kvm_page_fault: address 7fffb62ba318 error_code 2 >>>> qemu-system-x86-20240 [006] ...1 9406.484141: kvm_inj_exception: #DF (0x0) >>>> >>>> Second #PF at the same address and kvm injects the #DF. >>>> >>>> BUT(!), why? >>>> >>>> I probably am missing something but WTH are we pagefaulting at a >>>> user address in context_switch() while doing a lockdep call, i.e. >>>> spin_release? We're not touching any userspace gunk there AFAICT. >>>> >>>> Is this an async pagefault or so which kvm is doing so that the guest >>>> rip is actually pointing at the wrong place? >>>> >>> There is nothing in the trace that point to async pagefault as far as I see. >>> >>>> Or something else I'm missing, most probably... >>>> >>> Strange indeed. Can you also enable kvmmmu tracing? You can also instrument >>> kvm_multiple_exception() to see which two exception are combined into #DF. >>> >> >> FWIW, I'm seeing the same issue here (likely) on an E-450 APU. It >> disappears with older KVM (didn't bisect yet, some 3.11 is fine) and >> when patch-disabling the vmport in QEMU. >> >> Let me know if I can help with the analysis. >> > Bisection would be great of course. Once thing that is special about > vmport that comes to mind is that it reads vcpu registers to userspace and > write them back. IIRC "info registers" does the same. Can you see if the > problem is reproducible with disabled vmport, but doing "info registers" > in qemu console? Although trace does not should any exists to userspace > near the failure... Yes, info registers crashes the guest after a while as well (with different backtrace due to different context). Jan
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