Michael Ellerman wrote:
Nicholas Piggin <npiggin@xxxxxxxxx> writes:
On Sun, 8 Apr 2018 20:17:47 +1000
Balbir Singh <bsingharora@xxxxxxxxx> wrote:
On Fri, Apr 6, 2018 at 3:56 AM, Nicholas Piggin <npiggin@xxxxxxxxx> 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/
I'm afraid that won't actually help here :(
That series is specific to the function tracer, while this is using
static tracepoints.
We could convert trace_tlbie() to a TRACE_EVENT_CONDITION() and guard it
within a check for paca->ftrace_enabled, but that would only be useful
if the below callsites can ever be hit outside of KVM guest mode.
- Naveen
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