Re: [PATCH V9 03/18] perf/x86/intel: Handle guest PEBS overflow PMI for KVM guest

[Liuxiangdong]

On 2021/7/22 13:41, Zhu Lingshan wrote:
> From: Like Xu <like.xu@xxxxxxxxxxxxxxx>
>
> With PEBS virtualization, the guest PEBS records get delivered to the
> guest DS, and the host pmi handler uses perf_guest_cbs->is_in_guest()
> to distinguish whether the PMI comes from the guest code like Intel PT.
>
> No matter how many guest PEBS counters are overflowed, only triggering
> one fake event is enough. The fake event causes the KVM PMI callback to
> be called, thereby injecting the PEBS overflow PMI into the guest.
>
> KVM may inject the PMI with BUFFER_OVF set, even if the guest DS is
> empty. That should really be harmless. Thus guest PEBS handler would
> retrieve the correct information from its own PEBS records buffer.
>
> Originally-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> Co-developed-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
> Signed-off-by: Zhu Lingshan <lingshan.zhu@xxxxxxxxx>
> ---
>   arch/x86/events/intel/core.c | 45 ++++++++++++++++++++++++++++++++++++
>   1 file changed, 45 insertions(+)
>
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index da835f5a37e2..2eceb73cd303 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -2783,6 +2783,50 @@ static void intel_pmu_reset(void)
>   }
>   
>   DECLARE_STATIC_CALL(x86_guest_handle_intel_pt_intr, *(perf_guest_cbs->handle_intel_pt_intr));
> +DECLARE_STATIC_CALL(x86_guest_state, *(perf_guest_cbs->state));
> +
> +/*
> + * We may be running with guest PEBS events created by KVM, and the
> + * PEBS records are logged into the guest's DS and invisible to host.
> + *
> + * In the case of guest PEBS overflow, we only trigger a fake event
> + * to emulate the PEBS overflow PMI for guest PBES counters in KVM.
> + * The guest will then vm-entry and check the guest DS area to read
> + * the guest PEBS records.
> + *
> + * The contents and other behavior of the guest event do not matter.
> + */
> +static void x86_pmu_handle_guest_pebs(struct pt_regs *regs,
> +				      struct perf_sample_data *data)
> +{
> +	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> +	u64 guest_pebs_idxs = cpuc->pebs_enabled & ~cpuc->intel_ctrl_host_mask;

guest_pebs_idxs has been defined here.

> +	struct perf_event *event = NULL;
> +	unsigned int guest = 0;
> +	int bit;
> +
> +	guest = static_call(x86_guest_state)();
> +	if (!(guest & PERF_GUEST_ACTIVE))
> +		return;
> +
> +	if (!x86_pmu.pebs_vmx || !x86_pmu.pebs_active ||
> +	    !(cpuc->pebs_enabled & ~cpuc->intel_ctrl_host_mask))
> +		return;
> +
Why not use guest_pebs_idxs?

+	if (!x86_pmu.pebs_vmx || !x86_pmu.pebs_active ||
+	    !guest_pebs_idxs)
+		return;


> +	for_each_set_bit(bit, (unsigned long *)&guest_pebs_idxs,
> +			 INTEL_PMC_IDX_FIXED + x86_pmu.num_counters_fixed) {
> +		event = cpuc->events[bit];
> +		if (!event->attr.precise_ip)
> +			continue;
> +
> +		perf_sample_data_init(data, 0, event->hw.last_period);
> +		if (perf_event_overflow(event, data, regs))
> +			x86_pmu_stop(event, 0);
> +
> +		/* Inject one fake event is enough. */
> +		break;
> +	}
> +}
>   
>   static int handle_pmi_common(struct pt_regs *regs, u64 status)
>   {
> @@ -2835,6 +2879,7 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
>   		u64 pebs_enabled = cpuc->pebs_enabled;
>   
>   		handled++;
> +		x86_pmu_handle_guest_pebs(regs, &data);
>   		x86_pmu.drain_pebs(regs, &data);
>   		status &= intel_ctrl | GLOBAL_STATUS_TRACE_TOPAPMI;
>