On 8/1/2024 12:58 PM, Mingwei Zhang wrote:
> From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
>
> Current perf doesn't explicitly schedule out all exclude_guest events
> while the guest is running. There is no problem with the current
> emulated vPMU. Because perf owns all the PMU counters. It can mask the
> counter which is assigned to an exclude_guest event when a guest is
> running (Intel way), or set the corresponding HOSTONLY bit in evsentsel
> (AMD way). The counter doesn't count when a guest is running.
>
> However, either way doesn't work with the introduced passthrough vPMU.
> A guest owns all the PMU counters when it's running. The host should not
> mask any counters. The counter may be used by the guest. The evsentsel
> may be overwritten.
>
> Perf should explicitly schedule out all exclude_guest events to release
> the PMU resources when entering a guest, and resume the counting when
> exiting the guest.
>
> It's possible that an exclude_guest event is created when a guest is
> running. The new event should not be scheduled in as well.
>
> The ctx time is shared among different PMUs. The time cannot be stopped
> when a guest is running. It is required to calculate the time for events
> from other PMUs, e.g., uncore events. Add timeguest to track the guest
> run time. For an exclude_guest event, the elapsed time equals
> the ctx time - guest time.
> Cgroup has dedicated times. Use the same method to deduct the guest time
> from the cgroup time as well.
>
> Co-developed-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
> ---
> include/linux/perf_event.h | 6 ++
> kernel/events/core.c | 178 +++++++++++++++++++++++++++++++------
> 2 files changed, 155 insertions(+), 29 deletions(-)
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index e22cdb6486e6..81a5f8399cb8 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -952,6 +952,11 @@ struct perf_event_context {
> */
> struct perf_time_ctx time;
>
> + /*
> + * Context clock, runs when in the guest mode.
> + */
> + struct perf_time_ctx timeguest;
> +
> /*
> * These fields let us detect when two contexts have both
> * been cloned (inherited) from a common ancestor.
> @@ -1044,6 +1049,7 @@ struct bpf_perf_event_data_kern {
> */
> struct perf_cgroup_info {
> struct perf_time_ctx time;
> + struct perf_time_ctx timeguest;
> int active;
> };
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index c25e2bf27001..57648736e43e 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -376,7 +376,8 @@ enum event_type_t {
> /* see ctx_resched() for details */
> EVENT_CPU = 0x8,
> EVENT_CGROUP = 0x10,
> - EVENT_FLAGS = EVENT_CGROUP,
> + EVENT_GUEST = 0x20,
> + EVENT_FLAGS = EVENT_CGROUP | EVENT_GUEST,
> EVENT_ALL = EVENT_FLEXIBLE | EVENT_PINNED,
> };
>
> @@ -407,6 +408,7 @@ static atomic_t nr_include_guest_events __read_mostly;
>
> static atomic_t nr_mediated_pmu_vms;
> static DEFINE_MUTEX(perf_mediated_pmu_mutex);
> +static DEFINE_PER_CPU(bool, perf_in_guest);
>
> /* !exclude_guest event of PMU with PERF_PMU_CAP_PASSTHROUGH_VPMU */
> static inline bool is_include_guest_event(struct perf_event *event)
> @@ -706,6 +708,10 @@ static bool perf_skip_pmu_ctx(struct perf_event_pmu_context *pmu_ctx,
> if ((event_type & EVENT_CGROUP) && !pmu_ctx->nr_cgroups)
> return true;
>
> + if ((event_type & EVENT_GUEST) &&
> + !(pmu_ctx->pmu->capabilities & PERF_PMU_CAP_PASSTHROUGH_VPMU))
> + return true;
> +
> return false;
> }
>
> @@ -770,12 +776,21 @@ static inline int is_cgroup_event(struct perf_event *event)
> return event->cgrp != NULL;
> }
>
> +static inline u64 __perf_event_time_ctx(struct perf_event *event,
> + struct perf_time_ctx *time,
> + struct perf_time_ctx *timeguest);
> +
> +static inline u64 __perf_event_time_ctx_now(struct perf_event *event,
> + struct perf_time_ctx *time,
> + struct perf_time_ctx *timeguest,
> + u64 now);
> +
> static inline u64 perf_cgroup_event_time(struct perf_event *event)
> {
> struct perf_cgroup_info *t;
>
> t = per_cpu_ptr(event->cgrp->info, event->cpu);
> - return t->time.time;
> + return __perf_event_time_ctx(event, &t->time, &t->timeguest);
> }
>
> static inline u64 perf_cgroup_event_time_now(struct perf_event *event, u64 now)
> @@ -784,9 +799,9 @@ static inline u64 perf_cgroup_event_time_now(struct perf_event *event, u64 now)
>
> t = per_cpu_ptr(event->cgrp->info, event->cpu);
> if (!__load_acquire(&t->active))
> - return t->time.time;
> - now += READ_ONCE(t->time.offset);
> - return now;
> + return __perf_event_time_ctx(event, &t->time, &t->timeguest);
> +
> + return __perf_event_time_ctx_now(event, &t->time, &t->timeguest, now);
> }
>
> static inline void update_perf_time_ctx(struct perf_time_ctx *time, u64 now, bool adv);
> @@ -796,6 +811,18 @@ static inline void __update_cgrp_time(struct perf_cgroup_info *info, u64 now, bo
> update_perf_time_ctx(&info->time, now, adv);
> }
>
> +static inline void __update_cgrp_guest_time(struct perf_cgroup_info *info, u64 now, bool adv)
> +{
> + update_perf_time_ctx(&info->timeguest, now, adv);
> +}
> +
> +static inline void update_cgrp_time(struct perf_cgroup_info *info, u64 now)
> +{
> + __update_cgrp_time(info, now, true);
> + if (__this_cpu_read(perf_in_guest))
> + __update_cgrp_guest_time(info, now, true);
> +}
> +
> static inline void update_cgrp_time_from_cpuctx(struct perf_cpu_context *cpuctx, bool final)
> {
> struct perf_cgroup *cgrp = cpuctx->cgrp;
> @@ -809,7 +836,7 @@ static inline void update_cgrp_time_from_cpuctx(struct perf_cpu_context *cpuctx,
> cgrp = container_of(css, struct perf_cgroup, css);
> info = this_cpu_ptr(cgrp->info);
>
> - __update_cgrp_time(info, now, true);
> + update_cgrp_time(info, now);
> if (final)
> __store_release(&info->active, 0);
> }
> @@ -832,11 +859,11 @@ static inline void update_cgrp_time_from_event(struct perf_event *event)
> * Do not update time when cgroup is not active
> */
> if (info->active)
> - __update_cgrp_time(info, perf_clock(), true);
> + update_cgrp_time(info, perf_clock());
> }
>
> static inline void
> -perf_cgroup_set_timestamp(struct perf_cpu_context *cpuctx)
> +perf_cgroup_set_timestamp(struct perf_cpu_context *cpuctx, bool guest)
> {
> struct perf_event_context *ctx = &cpuctx->ctx;
> struct perf_cgroup *cgrp = cpuctx->cgrp;
> @@ -856,8 +883,12 @@ perf_cgroup_set_timestamp(struct perf_cpu_context *cpuctx)
> for (css = &cgrp->css; css; css = css->parent) {
> cgrp = container_of(css, struct perf_cgroup, css);
> info = this_cpu_ptr(cgrp->info);
> - __update_cgrp_time(info, ctx->time.stamp, false);
> - __store_release(&info->active, 1);
> + if (guest) {
> + __update_cgrp_guest_time(info, ctx->time.stamp, false);
> + } else {
> + __update_cgrp_time(info, ctx->time.stamp, false);
> + __store_release(&info->active, 1);
> + }
> }
> }
>
> @@ -1061,7 +1092,7 @@ static inline int perf_cgroup_connect(pid_t pid, struct perf_event *event,
> }
>
> static inline void
> -perf_cgroup_set_timestamp(struct perf_cpu_context *cpuctx)
> +perf_cgroup_set_timestamp(struct perf_cpu_context *cpuctx, bool guest)
> {
> }
>
> @@ -1488,16 +1519,34 @@ static inline void update_perf_time_ctx(struct perf_time_ctx *time, u64 now, boo
> */
> static void __update_context_time(struct perf_event_context *ctx, bool adv)
> {
> - u64 now = perf_clock();
> + lockdep_assert_held(&ctx->lock);
> +
> + update_perf_time_ctx(&ctx->time, perf_clock(), adv);
> +}
>
> +static void __update_context_guest_time(struct perf_event_context *ctx, bool adv)
> +{
> lockdep_assert_held(&ctx->lock);
>
> - update_perf_time_ctx(&ctx->time, now, adv);
> + /* must be called after __update_context_time(); */
> + update_perf_time_ctx(&ctx->timeguest, ctx->time.stamp, adv);
> }
>
> static void update_context_time(struct perf_event_context *ctx)
> {
> __update_context_time(ctx, true);
> + if (__this_cpu_read(perf_in_guest))
> + __update_context_guest_time(ctx, true);
> +}
> +
> +static inline u64 __perf_event_time_ctx(struct perf_event *event,
> + struct perf_time_ctx *time,
> + struct perf_time_ctx *timeguest)
> +{
> + if (event->attr.exclude_guest)
> + return time->time - timeguest->time;
> + else
> + return time->time;
> }
>
> static u64 perf_event_time(struct perf_event *event)
> @@ -1510,7 +1559,26 @@ static u64 perf_event_time(struct perf_event *event)
> if (is_cgroup_event(event))
> return perf_cgroup_event_time(event);
>
> - return ctx->time.time;
> + return __perf_event_time_ctx(event, &ctx->time, &ctx->timeguest);
> +}
> +
> +static inline u64 __perf_event_time_ctx_now(struct perf_event *event,
> + struct perf_time_ctx *time,
> + struct perf_time_ctx *timeguest,
> + u64 now)
> +{
> + /*
> + * The exclude_guest event time should be calculated from
> + * the ctx time - the guest time.
> + * The ctx time is now + READ_ONCE(time->offset).
> + * The guest time is now + READ_ONCE(timeguest->offset).
> + * So the exclude_guest time is
> + * READ_ONCE(time->offset) - READ_ONCE(timeguest->offset).
> + */
> + if (event->attr.exclude_guest && __this_cpu_read(perf_in_guest))
Hi Kan,
we see the following the warning when run perf record command after
enabling "CONFIG_DEBUG_PREEMPT" config item.
[ 166.779208] BUG: using __this_cpu_read() in preemptible [00000000] code:
perf/9494
[ 166.779234] caller is __this_cpu_preempt_check+0x13/0x20
[ 166.779241] CPU: 56 UID: 0 PID: 9494 Comm: perf Not tainted
6.11.0-rc4-perf-next-mediated-vpmu-v3+ #80
[ 166.779245] Hardware name: Quanta Cloud Technology Inc. QuantaGrid
D54Q-2U/S6Q-MB-MPS, BIOS 3A11.uh 12/02/2022
[ 166.779248] Call Trace:
[ 166.779250] <TASK>
[ 166.779252] dump_stack_lvl+0x76/0xa0
[ 166.779260] dump_stack+0x10/0x20
[ 166.779267] check_preemption_disabled+0xd7/0xf0
[ 166.779273] __this_cpu_preempt_check+0x13/0x20
[ 166.779279] calc_timer_values+0x193/0x200
[ 166.779287] perf_event_update_userpage+0x4b/0x170
[ 166.779294] ? ring_buffer_attach+0x14c/0x200
[ 166.779301] perf_mmap+0x533/0x5d0
[ 166.779309] mmap_region+0x243/0xaa0
[ 166.779322] do_mmap+0x35b/0x640
[ 166.779333] vm_mmap_pgoff+0xf0/0x1c0
[ 166.779345] ksys_mmap_pgoff+0x17a/0x250
[ 166.779354] __x64_sys_mmap+0x33/0x70
[ 166.779362] x64_sys_call+0x1fa4/0x25f0
[ 166.779369] do_syscall_64+0x70/0x130
The season that kernel complains this is __perf_event_time_ctx_now() calls
__this_cpu_read() in preemption enabled context.
To eliminate the warning, we may need to use this_cpu_read() to replace
__this_cpu_read().
diff --git a/kernel/events/core.c b/kernel/events/core.c
index ccd61fd06e8d..1eb628f8b3a0 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1581,7 +1581,7 @@ static inline u64 __perf_event_time_ctx_now(struct
perf_event *event,
* So the exclude_guest time is
* READ_ONCE(time->offset) - READ_ONCE(timeguest->offset).
*/
- if (event->attr.exclude_guest && __this_cpu_read(perf_in_guest))
+ if (event->attr.exclude_guest && this_cpu_read(perf_in_guest))
return READ_ONCE(time->offset) - READ_ONCE(timeguest->offset);
else
return now + READ_ONCE(time->offset);
> + return READ_ONCE(time->offset) - READ_ONCE(timeguest->offset);
> + else
> + return now + READ_ONCE(time->offset);
> }
>
> static u64 perf_event_time_now(struct perf_event *event, u64 now)
> @@ -1524,10 +1592,9 @@ static u64 perf_event_time_now(struct perf_event *event, u64 now)
> return perf_cgroup_event_time_now(event, now);
>
> if (!(__load_acquire(&ctx->is_active) & EVENT_TIME))
> - return ctx->time.time;
> + return __perf_event_time_ctx(event, &ctx->time, &ctx->timeguest);
>
> - now += READ_ONCE(ctx->time.offset);
> - return now;
> + return __perf_event_time_ctx_now(event, &ctx->time, &ctx->timeguest, now);
> }
>
> static enum event_type_t get_event_type(struct perf_event *event)
> @@ -3334,9 +3401,15 @@ ctx_sched_out(struct perf_event_context *ctx, enum event_type_t event_type)
> * would only update time for the pinned events.
> */
> if (is_active & EVENT_TIME) {
> + bool stop;
> +
> + /* vPMU should not stop time */
> + stop = !(event_type & EVENT_GUEST) &&
> + ctx == &cpuctx->ctx;
> +
> /* update (and stop) ctx time */
> update_context_time(ctx);
> - update_cgrp_time_from_cpuctx(cpuctx, ctx == &cpuctx->ctx);
> + update_cgrp_time_from_cpuctx(cpuctx, stop);
> /*
> * CPU-release for the below ->is_active store,
> * see __load_acquire() in perf_event_time_now()
> @@ -3354,7 +3427,18 @@ ctx_sched_out(struct perf_event_context *ctx, enum event_type_t event_type)
> cpuctx->task_ctx = NULL;
> }
>
> - is_active ^= ctx->is_active; /* changed bits */
> + if (event_type & EVENT_GUEST) {
> + /*
> + * Schedule out all !exclude_guest events of PMU
> + * with PERF_PMU_CAP_PASSTHROUGH_VPMU.
> + */
> + is_active = EVENT_ALL;
> + __update_context_guest_time(ctx, false);
> + perf_cgroup_set_timestamp(cpuctx, true);
> + barrier();
> + } else {
> + is_active ^= ctx->is_active; /* changed bits */
> + }
>
> list_for_each_entry(pmu_ctx, &ctx->pmu_ctx_list, pmu_ctx_entry) {
> if (perf_skip_pmu_ctx(pmu_ctx, event_type))
> @@ -3853,10 +3937,15 @@ static inline void group_update_userpage(struct perf_event *group_event)
> event_update_userpage(event);
> }
>
> +struct merge_sched_data {
> + int can_add_hw;
> + enum event_type_t event_type;
> +};
> +
> static int merge_sched_in(struct perf_event *event, void *data)
> {
> struct perf_event_context *ctx = event->ctx;
> - int *can_add_hw = data;
> + struct merge_sched_data *msd = data;
>
> if (event->state <= PERF_EVENT_STATE_OFF)
> return 0;
> @@ -3864,13 +3953,22 @@ static int merge_sched_in(struct perf_event *event, void *data)
> if (!event_filter_match(event))
> return 0;
>
> - if (group_can_go_on(event, *can_add_hw)) {
> + /*
> + * Don't schedule in any exclude_guest events of PMU with
> + * PERF_PMU_CAP_PASSTHROUGH_VPMU, while a guest is running.
> + */
> + if (__this_cpu_read(perf_in_guest) && event->attr.exclude_guest &&
> + event->pmu->capabilities & PERF_PMU_CAP_PASSTHROUGH_VPMU &&
> + !(msd->event_type & EVENT_GUEST))
> + return 0;
> +
> + if (group_can_go_on(event, msd->can_add_hw)) {
> if (!group_sched_in(event, ctx))
> list_add_tail(&event->active_list, get_event_list(event));
> }
>
> if (event->state == PERF_EVENT_STATE_INACTIVE) {
> - *can_add_hw = 0;
> + msd->can_add_hw = 0;
> if (event->attr.pinned) {
> perf_cgroup_event_disable(event, ctx);
> perf_event_set_state(event, PERF_EVENT_STATE_ERROR);
> @@ -3889,11 +3987,15 @@ static int merge_sched_in(struct perf_event *event, void *data)
>
> static void pmu_groups_sched_in(struct perf_event_context *ctx,
> struct perf_event_groups *groups,
> - struct pmu *pmu)
> + struct pmu *pmu,
> + enum event_type_t event_type)
> {
> - int can_add_hw = 1;
> + struct merge_sched_data msd = {
> + .can_add_hw = 1,
> + .event_type = event_type,
> + };
> visit_groups_merge(ctx, groups, smp_processor_id(), pmu,
> - merge_sched_in, &can_add_hw);
> + merge_sched_in, &msd);
> }
>
> static void ctx_groups_sched_in(struct perf_event_context *ctx,
> @@ -3905,14 +4007,14 @@ static void ctx_groups_sched_in(struct perf_event_context *ctx,
> list_for_each_entry(pmu_ctx, &ctx->pmu_ctx_list, pmu_ctx_entry) {
> if (perf_skip_pmu_ctx(pmu_ctx, event_type))
> continue;
> - pmu_groups_sched_in(ctx, groups, pmu_ctx->pmu);
> + pmu_groups_sched_in(ctx, groups, pmu_ctx->pmu, event_type);
> }
> }
>
> static void __pmu_ctx_sched_in(struct perf_event_context *ctx,
> struct pmu *pmu)
> {
> - pmu_groups_sched_in(ctx, &ctx->flexible_groups, pmu);
> + pmu_groups_sched_in(ctx, &ctx->flexible_groups, pmu, 0);
> }
>
> static void
> @@ -3927,9 +4029,11 @@ ctx_sched_in(struct perf_event_context *ctx, enum event_type_t event_type)
> return;
>
> if (!(is_active & EVENT_TIME)) {
> + /* EVENT_TIME should be active while the guest runs */
> + WARN_ON_ONCE(event_type & EVENT_GUEST);
> /* start ctx time */
> __update_context_time(ctx, false);
> - perf_cgroup_set_timestamp(cpuctx);
> + perf_cgroup_set_timestamp(cpuctx, false);
> /*
> * CPU-release for the below ->is_active store,
> * see __load_acquire() in perf_event_time_now()
> @@ -3945,7 +4049,23 @@ ctx_sched_in(struct perf_event_context *ctx, enum event_type_t event_type)
> WARN_ON_ONCE(cpuctx->task_ctx != ctx);
> }
>
> - is_active ^= ctx->is_active; /* changed bits */
> + if (event_type & EVENT_GUEST) {
> + /*
> + * Schedule in all !exclude_guest events of PMU
> + * with PERF_PMU_CAP_PASSTHROUGH_VPMU.
> + */
> + is_active = EVENT_ALL;
> +
> + /*
> + * Update ctx time to set the new start time for
> + * the exclude_guest events.
> + */
> + update_context_time(ctx);
> + update_cgrp_time_from_cpuctx(cpuctx, false);
> + barrier();
> + } else {
> + is_active ^= ctx->is_active; /* changed bits */
> + }
>
> /*
> * First go through the list and put on any pinned groups
