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

[Michael Ellerman]

Nicholas Piggin <npiggin at gmail.com> writes:

> On Sun, 8 Apr 2018 20:17:47 +1000
> Balbir Singh <bsingharora at gmail.com> wrote:
>
>> On Fri, Apr 6, 2018 at 3:56 AM, Nicholas Piggin <npiggin at 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.

Naveen has posted a series to (hopefully) fix this, which just missed
the merge window:

  https://patchwork.ozlabs.org/patch/894757/


cheers