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Date: Sun, 8 Apr 2018 23:41:50 +1000
From: Nicholas Piggin <npiggin@gmail.com>
To: Balbir Singh <bsingharora@gmail.com>
Cc: "open list:KERNEL VIRTUAL MACHINE (KVM) FOR POWERPC"
 <kvm-ppc@vger.kernel.org>, "open list:LINUX FOR POWERPC (32-BIT AND
 64-BIT)" <linuxppc-dev@lists.ozlabs.org>, Paul Mackerras
 <paulus@ozlabs.org>
Subject: Re: [PATCH 1/2] KVM: PPC: Book3S HV: trace_tlbie must not be called
 in realmode
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On Sun, 8 Apr 2018 20:17:47 +1000
Balbir Singh <bsingharora@gmail.com> wrote:

> On Fri, Apr 6, 2018 at 3:56 AM, Nicholas Piggin <npiggin@gmail.com> wrote:
> > This crashes with a "Bad real address for load" attempting to load
> > from the vmalloc region in realmode (faulting address is in DAR).
> >
> >   Oops: Bad interrupt in KVM entry/exit code, sig: 6 [#1]
> >   LE SMP NR_CPUS=2048 NUMA PowerNV
> >   CPU: 53 PID: 6582 Comm: qemu-system-ppc Not tainted 4.16.0-01530-g43d1859f0994
> >   NIP:  c0000000000155ac LR: c0000000000c2430 CTR: c000000000015580
> >   REGS: c000000fff76dd80 TRAP: 0200   Not tainted  (4.16.0-01530-g43d1859f0994)
> >   MSR:  9000000000201003 <SF,HV,ME,RI,LE>  CR: 48082222  XER: 00000000
> >   CFAR: 0000000102900ef0 DAR: d00017fffd941a28 DSISR: 00000040 SOFTE: 3
> >   NIP [c0000000000155ac] perf_trace_tlbie+0x2c/0x1a0
> >   LR [c0000000000c2430] do_tlbies+0x230/0x2f0
> >
> > I suspect the reason is the per-cpu data is not in the linear chunk.
> > This could be restored if that was able to be fixed, but for now,
> > just remove the tracepoints.  
> 
> Could you share the stack trace as well? I've not observed this in my testing.

I can't seem to find it, I can try reproduce tomorrow. It was coming
from h_remove hcall from the guest. It's 176 logical CPUs.

> May be I don't have as many cpus. I presume your talking about the per cpu
> data offsets for per cpu trace data?

It looked like it was dereferencing virtually mapped per-cpu data, yes.
Probably the perf_events deref.

Thanks,
Nick