Re: [PATCH 1/2] KVM: PPC: Book3S HV: trace_tlbie must not be called in realmode

On Sun, 8 Apr 2018 20:17:47 +1000
Balbir Singh [off-list ref] wrote:

On Fri, Apr 6, 2018 at 3:56 AM, Nicholas Piggin [off-list ref] wrote:

quoted

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