Use PERF_CONTEXT_{KERNEL, GUEST} in some way.

[cvonelm]

Something I have discovered almost by accident is that if you do callstack sampling with lo2s, perf will put marker events with Instruction Pointer value PERF_CONTEXT_{KERNEL, USER ...} on the callstack. (The numeric IP value is something very high like 0xffff fffe0).

These events denote the border between IPs in the callstack in the kernel and userspace.

In an upcoming patch, I have simply decided to filter them out for now. One idea Mario had was to write marker CallingContext events in their place like [kernel_begin].