On Thu, May 16, 2019 at 02:21:45PM +0100, Raphael Gault wrote: > In order to be able to access the counter directly for userspace, > we need to provide the index of the counter using the userpage. > We thus need to override the event_idx function to retrieve and > convert the perf_event index to armv8 hardware index.
It would be worth noting that since the arm_pmu framework can be used with other versions of the PMU architecture which could not permit safe userspace access, we allow the arch code to opt-in with the ARMPMU_EL0_RD_CNTR flag. > Signed-off-by: Raphael Gault <[email protected]> > --- > arch/arm64/kernel/perf_event.c | 4 ++++ > drivers/perf/arm_pmu.c | 10 ++++++++++ > include/linux/perf/arm_pmu.h | 2 ++ > 3 files changed, 16 insertions(+) > > diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c > index 6164d389eed6..e6316f99f66b 100644 > --- a/arch/arm64/kernel/perf_event.c > +++ b/arch/arm64/kernel/perf_event.c > @@ -890,6 +890,8 @@ static int __armv8_pmuv3_map_event(struct perf_event > *event, > if (armv8pmu_event_is_64bit(event)) > event->hw.flags |= ARMPMU_EVT_64BIT; > > + event->hw.flags |= ARMPMU_EL0_RD_CNTR; > + > /* Only expose micro/arch events supported by this PMU */ > if ((hw_event_id > 0) && (hw_event_id < ARMV8_PMUV3_MAX_COMMON_EVENTS) > && test_bit(hw_event_id, armpmu->pmceid_bitmap)) { > @@ -1188,6 +1190,8 @@ void arch_perf_update_userpage(struct perf_event *event, > */ > freq = arch_timer_get_rate(); > userpg->cap_user_time = 1; > + userpg->cap_user_rdpmc = > + !!(event->hw.flags & ARMPMU_EL0_RD_CNTR); This is under 80 columns when placed on a single line, so it doesn't need to be split here. > > clocks_calc_mult_shift(&userpg->time_mult, &shift, freq, > NSEC_PER_SEC, 0); > diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c > index eec75b97e7ea..3f4c2ec7ff89 100644 > --- a/drivers/perf/arm_pmu.c > +++ b/drivers/perf/arm_pmu.c > @@ -777,6 +777,15 @@ static void cpu_pmu_destroy(struct arm_pmu *cpu_pmu) > &cpu_pmu->node); > } > > + > +static int armpmu_event_idx(struct perf_event *event) > +{ > + if (!(event->hw.flags & ARMPMU_EL0_RD_CNTR)) > + return 0; > + > + return event->hw.idx; I think this needs to remap ARMV8_IDX_CYCLE_COUNTER to 32, to match the offset applie to the rest of counter indices. Otherwise, this looks good to me. Thanks, Mark. > +} > + > static struct arm_pmu *__armpmu_alloc(gfp_t flags) > { > struct arm_pmu *pmu; > @@ -803,6 +812,7 @@ static struct arm_pmu *__armpmu_alloc(gfp_t flags) > .start = armpmu_start, > .stop = armpmu_stop, > .read = armpmu_read, > + .event_idx = armpmu_event_idx, > .filter_match = armpmu_filter_match, > .attr_groups = pmu->attr_groups, > /* > diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h > index 4641e850b204..3bef390c1069 100644 > --- a/include/linux/perf/arm_pmu.h > +++ b/include/linux/perf/arm_pmu.h > @@ -30,6 +30,8 @@ > */ > /* Event uses a 64bit counter */ > #define ARMPMU_EVT_64BIT 1 > +/* Allow access to hardware counter from userspace */ > +#define ARMPMU_EL0_RD_CNTR 2 > > #define HW_OP_UNSUPPORTED 0xFFFF > #define C(_x) PERF_COUNT_HW_CACHE_##_x > -- > 2.17.1 >
