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Message-ID: <20230528110516.GC886420@leoy-yangtze.lan>
Date: Sun, 28 May 2023 19:05:16 +0800
From: Leo Yan <leo.yan@...aro.org>
To: James Clark <james.clark@....com>
Cc: coresight@...ts.linaro.org, denik@...omium.org,
Suzuki K Poulose <suzuki.poulose@....com>,
Mike Leach <mike.leach@...aro.org>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>,
John Garry <john.g.garry@...cle.com>,
Will Deacon <will@...nel.org>,
linux-arm-kernel@...ts.infradead.org,
linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] perf cs-etm: Track exception level
On Wed, May 24, 2023 at 02:19:57PM +0100, James Clark wrote:
> Currently we assume all trace belongs to the host machine so when
> the decoder should be looking at the guest kernel maps it can crash
> because it looks at the host ones instead.
>
> Avoid one scenario (guest kernel running at EL1) by assigning the
> default guest machine to this trace. For userspace trace it's still not
> possible to determine guest vs host, but the PIDs should help in this
> case.
>
> Signed-off-by: James Clark <james.clark@....com>
> ---
> .../perf/util/cs-etm-decoder/cs-etm-decoder.c | 7 +-
> tools/perf/util/cs-etm.c | 64 ++++++++++++++-----
> tools/perf/util/cs-etm.h | 5 +-
> 3 files changed, 56 insertions(+), 20 deletions(-)
>
> diff --git a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> index 82a27ab90c8b..ac227cd03eb0 100644
> --- a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> +++ b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> @@ -573,12 +573,13 @@ cs_etm_decoder__set_tid(struct cs_etm_queue *etmq,
> break;
> }
>
> + if (cs_etm__etmq_set_tid_el(etmq, tid, trace_chan_id,
> + elem->context.exception_level))
> + return OCSD_RESP_FATAL_SYS_ERR;
> +
> if (tid == -1)
> return OCSD_RESP_CONT;
>
> - if (cs_etm__etmq_set_tid(etmq, tid, trace_chan_id))
> - return OCSD_RESP_FATAL_SYS_ERR;
> -
> /*
> * A timestamp is generated after a PE_CONTEXT element so make sure
> * to rely on that coming one.
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index a997fe79d458..b9ba19327f26 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -14,7 +14,6 @@
> #include <linux/types.h>
> #include <linux/zalloc.h>
>
> -#include <opencsd/ocsd_if_types.h>
> #include <stdlib.h>
>
> #include "auxtrace.h"
> @@ -87,6 +86,8 @@ struct cs_etm_traceid_queue {
> union perf_event *event_buf;
> struct thread *thread;
> struct thread *prev_thread;
> + ocsd_ex_level prev_el;
> + ocsd_ex_level el;
> struct branch_stack *last_branch;
> struct branch_stack *last_branch_rb;
> struct cs_etm_packet *prev_packet;
> @@ -479,6 +480,7 @@ static int cs_etm__init_traceid_queue(struct cs_etm_queue *etmq,
>
> queue = &etmq->etm->queues.queue_array[etmq->queue_nr];
> tidq->trace_chan_id = trace_chan_id;
> + tidq->el = tidq->prev_el = ocsd_EL_unknown;
> tidq->thread = machine__findnew_thread(&etm->session->machines.host, -1,
> queue->tid);
> tidq->prev_thread = machine__idle_thread(&etm->session->machines.host);
> @@ -618,6 +620,7 @@ static void cs_etm__packet_swap(struct cs_etm_auxtrace *etm,
> tmp = tidq->packet;
> tidq->packet = tidq->prev_packet;
> tidq->prev_packet = tmp;
> + tidq->prev_el = tidq->el;
> thread__put(tidq->prev_thread);
> tidq->prev_thread = thread__get(tidq->thread);
> }
> @@ -879,11 +882,34 @@ static bool cs_etm__evsel_is_auxtrace(struct perf_session *session,
> return evsel->core.attr.type == aux->pmu_type;
> }
>
> -static u8 cs_etm__cpu_mode(struct cs_etm_queue *etmq, u64 address)
> +static struct machine *cs_etm__get_machine(struct cs_etm_auxtrace *etm,
> + ocsd_ex_level el)
> {
> - struct machine *machine;
> + /*
> + * Not perfect, but assume anything in EL1 is the default guest, and
> + * everything else is the host. nHVE and pKVM may not work with this
s/nHVE/nVHE ?
And it's good to say "if any virtulisation (e.g. pKVM) based on nVHE may
not work with this ....".
> + * assumption. And distinguishing between guest and host userspaces
> + * isn't currently supported either. Neither is multiple guest support.
> + * All this does is reduce the likeliness of decode errors where we look
> + * into the host kernel maps when it should have been the guest maps.
> + */
> + switch (el) {
> + case ocsd_EL1:
> + return machines__find_guest(&etm->session->machines,
> + DEFAULT_GUEST_KERNEL_ID);
I share the same concern with Mike that this will break perf for any
Armv8 CPUs with nVHE (like Cortex-CA53, etc).
You could see CoreSight has trace data "elem->context.vmid", when a
guest kernel runs in EL1, can we use "elem->context.vmid" as a guest
kernel ID and finally retrieve the corresponding machine pointer?
Thanks,
Leo
> + case ocsd_EL3:
> + case ocsd_EL2:
> + case ocsd_EL0:
> + case ocsd_EL_unknown:
> + default:
> + return &etm->session->machines.host;
> + }
> +}
>
> - machine = &etmq->etm->session->machines.host;
> +static u8 cs_etm__cpu_mode(struct cs_etm_queue *etmq, u64 address,
> + ocsd_ex_level el)
> +{
> + struct machine *machine = cs_etm__get_machine(etmq->etm, el);
>
> if (address >= machine__kernel_start(machine)) {
> if (machine__is_host(machine))
> @@ -893,10 +919,14 @@ static u8 cs_etm__cpu_mode(struct cs_etm_queue *etmq, u64 address)
> } else {
> if (machine__is_host(machine))
> return PERF_RECORD_MISC_USER;
> - else if (perf_guest)
> + else {
> + /*
> + * Can't really happen at the moment because
> + * cs_etm__get_machine() will always return
> + * machines.host for any non EL1 trace.
> + */
> return PERF_RECORD_MISC_GUEST_USER;
> - else
> - return PERF_RECORD_MISC_HYPERVISOR;
> + }
> }
> }
>
> @@ -913,11 +943,12 @@ static u32 cs_etm__mem_access(struct cs_etm_queue *etmq, u8 trace_chan_id,
> if (!etmq)
> return 0;
>
> - cpumode = cs_etm__cpu_mode(etmq, address);
> tidq = cs_etm__etmq_get_traceid_queue(etmq, trace_chan_id);
> if (!tidq)
> return 0;
>
> + cpumode = cs_etm__cpu_mode(etmq, address, tidq->el);
> +
> if (!thread__find_map(tidq->thread, cpumode, address, &al))
> return 0;
>
> @@ -1296,9 +1327,10 @@ cs_etm__get_trace(struct cs_etm_queue *etmq)
> }
>
> static void cs_etm__set_thread(struct cs_etm_auxtrace *etm,
> - struct cs_etm_traceid_queue *tidq, pid_t tid)
> + struct cs_etm_traceid_queue *tidq, pid_t tid,
> + ocsd_ex_level el)
> {
> - struct machine *machine = &etm->session->machines.host;
> + struct machine *machine = cs_etm__get_machine(etm, el);
>
> if (tid != -1) {
> thread__zput(tidq->thread);
> @@ -1308,10 +1340,12 @@ static void cs_etm__set_thread(struct cs_etm_auxtrace *etm,
> /* Couldn't find a known thread */
> if (!tidq->thread)
> tidq->thread = machine__idle_thread(machine);
> +
> + tidq->el = el;
> }
>
> -int cs_etm__etmq_set_tid(struct cs_etm_queue *etmq,
> - pid_t tid, u8 trace_chan_id)
> +int cs_etm__etmq_set_tid_el(struct cs_etm_queue *etmq, pid_t tid, u8 trace_chan_id,
> + ocsd_ex_level el)
> {
> struct cs_etm_traceid_queue *tidq;
>
> @@ -1319,7 +1353,7 @@ int cs_etm__etmq_set_tid(struct cs_etm_queue *etmq,
> if (!tidq)
> return -EINVAL;
>
> - cs_etm__set_thread(etmq->etm, tidq, tid);
> + cs_etm__set_thread(etmq->etm, tidq, tid, el);
> return 0;
> }
>
> @@ -1389,7 +1423,7 @@ static int cs_etm__synth_instruction_sample(struct cs_etm_queue *etmq,
> struct perf_sample sample = {.ip = 0,};
>
> event->sample.header.type = PERF_RECORD_SAMPLE;
> - event->sample.header.misc = cs_etm__cpu_mode(etmq, addr);
> + event->sample.header.misc = cs_etm__cpu_mode(etmq, addr, tidq->el);
> event->sample.header.size = sizeof(struct perf_event_header);
>
> /* Set time field based on etm auxtrace config. */
> @@ -1448,7 +1482,7 @@ static int cs_etm__synth_branch_sample(struct cs_etm_queue *etmq,
> ip = cs_etm__last_executed_instr(tidq->prev_packet);
>
> event->sample.header.type = PERF_RECORD_SAMPLE;
> - event->sample.header.misc = cs_etm__cpu_mode(etmq, ip);
> + event->sample.header.misc = cs_etm__cpu_mode(etmq, ip, tidq->prev_el);
> event->sample.header.size = sizeof(struct perf_event_header);
>
> /* Set time field based on etm auxtrace config. */
> diff --git a/tools/perf/util/cs-etm.h b/tools/perf/util/cs-etm.h
> index 70cac0375b34..88e9b25a8a9f 100644
> --- a/tools/perf/util/cs-etm.h
> +++ b/tools/perf/util/cs-etm.h
> @@ -232,10 +232,11 @@ int cs_etm__process_auxtrace_info(union perf_event *event,
> struct perf_event_attr *cs_etm_get_default_config(struct perf_pmu *pmu);
>
> #ifdef HAVE_CSTRACE_SUPPORT
> +#include <opencsd/ocsd_if_types.h>
> int cs_etm__get_cpu(u8 trace_chan_id, int *cpu);
> int cs_etm__get_pid_fmt(u8 trace_chan_id, u64 *pid_fmt);
> -int cs_etm__etmq_set_tid(struct cs_etm_queue *etmq,
> - pid_t tid, u8 trace_chan_id);
> +int cs_etm__etmq_set_tid_el(struct cs_etm_queue *etmq, pid_t tid, u8 trace_chan_id,
> + ocsd_ex_level el);
> bool cs_etm__etmq_is_timeless(struct cs_etm_queue *etmq);
> void cs_etm__etmq_set_traceid_queue_timestamp(struct cs_etm_queue *etmq,
> u8 trace_chan_id);
> --
> 2.34.1
>
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