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

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Date:   Thu, 6 Aug 2020 13:00:46 +0200
From:   peterz@...radead.org
To:     "Jin, Yao" <yao.jin@...ux.intel.com>
Cc:     mingo@...hat.com, oleg@...hat.com, acme@...nel.org,
        jolsa@...nel.org, Linux-kernel@...r.kernel.org, ak@...ux.intel.com,
        kan.liang@...el.com, yao.jin@...el.com,
        alexander.shishkin@...ux.intel.com, mark.rutland@....com
Subject: Re: [PATCH v1 2/2] perf/core: Fake regs for leaked kernel samples

On Thu, Aug 06, 2020 at 11:18:27AM +0200, peterz@...radead.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?