[PATCH v9 03/10] perf/x86: Add constraint to create guest LBR event without hw counter

Like Xu
2020-03-13T02:19:04Z

The hypervisor may request the perf subsystem to schedule a time window
to directly access the LBR stack msrs for its own use. Normally, it would
create a guest LBR event with callstack mode enabled, which is scheduled
along with other LBR events on the host but in an exclusive way.

To avoid wasting a counter for the guest LBR event, the perf tracks it via
is_guest_lbr_event() and assigns it with a fake INTEL_PMC_IDX_FIXED_VLBR
counter with the help of new guest_lbr_constraint. Inspired by BTS event,
there is actually no hardware counter allocated for guest LBR events.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Like Xu <like.xu@linux.intel.com>
---
arch/x86/events/core.c | 9 ++++++---
arch/x86/events/intel/core.c | 19 +++++++++++++++++++
arch/x86/events/intel/lbr.c | 3 +++
arch/x86/events/perf_event.h | 15 +++++++++++++++
arch/x86/include/asm/perf_event.h | 12 +++++++++++-
include/linux/perf_event.h | 7 +++++++
kernel/events/core.c | 7 -------
7 files changed, 61 insertions(+), 11 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 3bb738f5a472..e919187a0751 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -74,7 +74,8 @@ u64 x86_perf_event_update(struct perf_event *event)
int idx = hwc->idx;
u64 delta;

- if (idx == INTEL_PMC_IDX_FIXED_BTS)
+ if ((idx == INTEL_PMC_IDX_FIXED_BTS) ||
+ (idx == INTEL_PMC_IDX_FIXED_VLBR))
return 0;

/*
@@ -1102,7 +1103,8 @@ static inline void x86_assign_hw_event(struct perf_event *event,
hwc->last_cpu = smp_processor_id();
hwc->last_tag = ++cpuc->tags[i];

- if (hwc->idx == INTEL_PMC_IDX_FIXED_BTS) {
+ if ((hwc->idx == INTEL_PMC_IDX_FIXED_BTS) ||
+ (hwc->idx == INTEL_PMC_IDX_FIXED_VLBR)) {
hwc->config_base = 0;
hwc->event_base = 0;
} else if (hwc->idx >= INTEL_PMC_IDX_FIXED) {
@@ -1233,7 +1235,8 @@ int x86_perf_event_set_period(struct perf_event *event)
s64 period = hwc->sample_period;
int ret = 0, idx = hwc->idx;

- if (idx == INTEL_PMC_IDX_FIXED_BTS)
+ if ((idx == INTEL_PMC_IDX_FIXED_BTS) ||
+ (idx == INTEL_PMC_IDX_FIXED_VLBR))
return 0;

/*
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 3be51aa06e67..901c82032f4a 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -2157,6 +2157,9 @@ static void intel_pmu_disable_event(struct perf_event *event)
return;
}

+ if (unlikely(hwc->idx == INTEL_PMC_IDX_FIXED_VLBR))
+ return;
+
cpuc->intel_ctrl_guest_mask &= ~(1ull << hwc->idx);
cpuc->intel_ctrl_host_mask &= ~(1ull << hwc->idx);
cpuc->intel_cp_status &= ~(1ull << hwc->idx);
@@ -2241,6 +2244,9 @@ static void intel_pmu_enable_event(struct perf_event *event)
return;
}

+ if (unlikely(hwc->idx == INTEL_PMC_IDX_FIXED_VLBR))
+ return;
+
if (event->attr.exclude_host)
cpuc->intel_ctrl_guest_mask |= (1ull << hwc->idx);
if (event->attr.exclude_guest)
@@ -2595,6 +2601,15 @@ intel_bts_constraints(struct perf_event *event)
return NULL;
}

+static struct event_constraint *
+intel_guest_event_constraints(struct perf_event *event)
+{
+ if (unlikely(is_guest_lbr_event(event)))
+ return &guest_lbr_constraint;
+
+ return NULL;
+}
+
static int intel_alt_er(int idx, u64 config)
{
int alt_idx = idx;
@@ -2785,6 +2800,10 @@ __intel_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
{
struct event_constraint *c;

+ c = intel_guest_event_constraints(event);
+ if (c)
+ return c;
+
c = intel_bts_constraints(event);
if (c)
return c;
diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
index 5ed88e578eaa..ff1f35b4f420 100644
--- a/arch/x86/events/intel/lbr.c
+++ b/arch/x86/events/intel/lbr.c
@@ -1353,3 +1353,6 @@ int x86_perf_get_lbr(struct x86_pmu_lbr *stack)
return 0;
}
EXPORT_SYMBOL_GPL(x86_perf_get_lbr);
+
+struct event_constraint guest_lbr_constraint =
+ EVENT_CONSTRAINT(0, 1ULL << GLOBAL_STATUS_LBRS_FROZEN_BIT, 0);
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index 1025bc6eb04f..9a62264a3068 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -969,6 +969,20 @@ static inline bool intel_pmu_has_bts(struct perf_event *event)
return intel_pmu_has_bts_period(event, hwc->sample_period);
}

+static inline bool is_guest_event(struct perf_event *event)
+{
+ if (event->attr.exclude_host && is_kernel_event(event))
+ return true;
+ return false;
+}
+
+static inline bool is_guest_lbr_event(struct perf_event *event)
+{
+ if (is_guest_event(event) && needs_branch_stack(event))
+ return true;
+ return false;
+}
+
int intel_pmu_save_and_restart(struct perf_event *event);

struct event_constraint *
@@ -989,6 +1003,7 @@ void release_ds_buffers(void);
void reserve_ds_buffers(void);

extern struct event_constraint bts_constraint;
+extern struct event_constraint guest_lbr_constraint;

void intel_pmu_enable_bts(u64 config);

diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index e018a1cf604c..674130aca75a 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -181,9 +181,19 @@ struct x86_pmu_capability {
#define GLOBAL_STATUS_UNC_OVF BIT_ULL(61)
#define GLOBAL_STATUS_ASIF BIT_ULL(60)
#define GLOBAL_STATUS_COUNTERS_FROZEN BIT_ULL(59)
-#define GLOBAL_STATUS_LBRS_FROZEN BIT_ULL(58)
+#define GLOBAL_STATUS_LBRS_FROZEN_BIT 58
+#define GLOBAL_STATUS_LBRS_FROZEN BIT_ULL(GLOBAL_STATUS_LBRS_FROZEN_BIT)
#define GLOBAL_STATUS_TRACE_TOPAPMI BIT_ULL(55)

+/*
+ * We model guest LBR event tracing as another fixed-mode PMC like BTS.
+ *
+ * We choose bit 58 (LBRS_FROZEN_BIT) which is used to indicate that the LBR
+ * stack is frozen on a hardware PMI request in the PERF_GLOBAL_STATUS msr,
+ * and the 59th PMC counter (if any) is not supposed to use it as well.
+ */
+#define INTEL_PMC_IDX_FIXED_VLBR GLOBAL_STATUS_LBRS_FROZEN_BIT
+
/*
* Adaptive PEBS v4
*/
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 547773f5894e..b94b695f2d7e 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1082,6 +1082,13 @@ static inline bool is_sampling_event(struct perf_event *event)
return event->attr.sample_period != 0;
}

+#define TASK_TOMBSTONE ((void *)-1L)
+
+static inline bool is_kernel_event(struct perf_event *event)
+{
+ return READ_ONCE(event->owner) == TASK_TOMBSTONE;
+}
+
/*
* Return 1 for a software event, 0 for a hardware event
*/
diff --git a/kernel/events/core.c b/kernel/events/core.c
index e453589da97c..75d47fcb9a0d 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -164,13 +164,6 @@ static void perf_ctx_unlock(struct perf_cpu_context *cpuctx,
raw_spin_unlock(&cpuctx->ctx.lock);
}

-#define TASK_TOMBSTONE ((void *)-1L)
-
-static bool is_kernel_event(struct perf_event *event)
-{
- return READ_ONCE(event->owner) == TASK_TOMBSTONE;
-}
-
/*
* On task ctx scheduling...
*
--
2.21.1