Re: [PATCH v1 2/2] perf/core: Fake regs for leaked kernel samples

peterz
2020-08-06T17:28:14Z

On Thu, Aug 06, 2020 at 11:18:27AM +0200, peterz@infradead.org wrote:

> Suppose we have nested virt:
>
> L0-hv
> |
> G0/L1-hv
> |
> G1
>
> And we're running in G0, then:
>
> - 'exclude_hv' would exclude L0 events
> - 'exclude_host' would ... exclude L1-hv events?
> - 'exclude_guest' would ... exclude G1 events?

So in arch/x86/events/intel/core.c we have:

static inline void intel_set_masks(struct perf_event *event, int idx)
{
struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);

if (event->attr.exclude_host)
__set_bit(idx, (unsigned long *)&cpuc->intel_ctrl_guest_mask);
if (event->attr.exclude_guest)
__set_bit(idx, (unsigned long *)&cpuc->intel_ctrl_host_mask);
if (event_is_checkpointed(event))
__set_bit(idx, (unsigned long *)&cpuc->intel_cp_status);
}

which is, afaict, just plain wrong. Should that not be something like:

if (!event->attr.exclude_host)
__set_bit(idx, (unsigned long *)&cpuc->intel_ctrl_host_mask);
if (!event->attr.exclude_guest)
__set_bit(idx, (unsigned long *)&cpuc->intel_ctrl_guest_mask);

Also, ARM64 seems to also implement this stuff, Mark, do you have any
insight on how all this is 'supposed' to work?