The hypervisor may request the perf subsystem to schedule a time window to directly access the LBR records msrs for its own use. Normally, it would create a guest LBR event with callstack mode enabled, which is scheduled along with other ordinary LBR events on the host but in an exclusive way. To avoid wasting a counter for the guest LBR event, the perf tracks its hw->idx via INTEL_PMC_IDX_FIXED_VLBR and assigns it with a fake VLBR counter with the help of new vlbr_constraint. As with the BTS event, there is actually no hardware counter assigned for the guest LBR event. Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Link: https://lkml.kernel.org/r/20200514083054.62538-5-like.xu@xxxxxxxxxxxxxxx --- arch/x86/events/core.c | 1 + arch/x86/events/intel/core.c | 18 ++++++++++++++++++ arch/x86/events/intel/lbr.c | 4 ++++ arch/x86/events/perf_event.h | 1 + arch/x86/include/asm/perf_event.h | 22 +++++++++++++++++++++- 5 files changed, 45 insertions(+), 1 deletion(-) diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index 9a5056472b67..1996f2ed7c83 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -1104,6 +1104,7 @@ static inline void x86_assign_hw_event(struct perf_event *event, switch (hwc->idx) { case INTEL_PMC_IDX_FIXED_BTS: + case INTEL_PMC_IDX_FIXED_VLBR: hwc->config_base = 0; hwc->event_base = 0; break; diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c index 8dac4c61bf76..51e1fba7b1d1 100644 --- a/arch/x86/events/intel/core.c +++ b/arch/x86/events/intel/core.c @@ -2621,6 +2621,20 @@ intel_bts_constraints(struct perf_event *event) return NULL; } +/* + * Note: matches a fake event, like Fixed2. + */ +static struct event_constraint * +intel_vlbr_constraints(struct perf_event *event) +{ + struct event_constraint *c = &vlbr_constraint; + + if (unlikely(constraint_match(c, event->hw.config))) + return c; + + return NULL; +} + static int intel_alt_er(int idx, u64 config) { int alt_idx = idx; @@ -2811,6 +2825,10 @@ __intel_get_event_constraints(struct cpu_hw_events *cpuc, int idx, { struct event_constraint *c; + c = intel_vlbr_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 2ed3f2a51bdf..d285d26c1578 100644 --- a/arch/x86/events/intel/lbr.c +++ b/arch/x86/events/intel/lbr.c @@ -1363,3 +1363,7 @@ int x86_perf_get_lbr(struct x86_pmu_lbr *lbr) return 0; } EXPORT_SYMBOL_GPL(x86_perf_get_lbr); + +struct event_constraint vlbr_constraint = + FIXED_EVENT_CONSTRAINT(INTEL_FIXED_VLBR_EVENT, + (INTEL_PMC_IDX_FIXED_VLBR - INTEL_PMC_IDX_FIXED)); diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h index eb37f6c43c96..77a6dd66bd9a 100644 --- a/arch/x86/events/perf_event.h +++ b/arch/x86/events/perf_event.h @@ -990,6 +990,7 @@ void release_ds_buffers(void); void reserve_ds_buffers(void); extern struct event_constraint bts_constraint; +extern struct event_constraint vlbr_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 5d2c30f0df02..2df707311d17 100644 --- a/arch/x86/include/asm/perf_event.h +++ b/arch/x86/include/asm/perf_event.h @@ -192,9 +192,29 @@ 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 because it's used to indicate LBR stack frozen state + * for architectural perfmon v4, also we unconditionally mask that bit in + * the handle_pmi_common(), so it'll never be set in the overflow handling. + * + * With this fake counter assigned, the guest LBR event user (such as KVM), + * can program the LBR registers on its own, and we don't actually do anything + * with then in the host context. + */ +#define INTEL_PMC_IDX_FIXED_VLBR (GLOBAL_STATUS_LBRS_FROZEN_BIT) + +/* + * Pseudo-encoding the guest LBR event as event=0x00,umask=0x1b, + * since it would claim bit 58 which is effectively Fixed26. + */ +#define INTEL_FIXED_VLBR_EVENT 0x1b00 + /* * Adaptive PEBS v4 */ -- 2.21.3
