[PATCH V13 00/14] perf/core: Add ability for an event to "pause" or "resume" AUX area tracing

Adrian Hunter
2024-10-14T10:51:48Z

Hi

Note for V12:
There was a small conflict between the Intel PT changes in
"KVM: x86: Fix Intel PT Host/Guest mode when host tracing" and the
changes in this patch set, so I have put the patch sets together,
along with outstanding fix "perf/x86/intel/pt: Fix buffer full but
size is 0 case"

Cover letter for KVM changes (patches 2 to 4):

There is a long-standing problem whereby running Intel PT on host and guest
in Host/Guest mode, causes VM-Entry failure.

The motivation for this patch set is to provide a fix for stable kernels
prior to the advent of the "Mediated Passthrough vPMU" patch set:

https://lore.kernel.org/kvm/20240801045907.4010984-1-mizhang@google.com/

which would render a large part of the fix unnecessary but likely not be
suitable for backport to stable due to its size and complexity.

Ideally, this patch set would be applied before "Mediated Passthrough vPMU"

Note that the fix does not conflict with "Mediated Passthrough vPMU", it
is just that "Mediated Passthrough vPMU" will make the code to stop and
restart Intel PT unnecessary.

Note for V11:
Moving aux_paused into a union within struct hw_perf_event caused
a regression because aux_paused was being written unconditionally
even though it is valid only for AUX (e.g. Intel PT) PMUs.
That is fixed in V11.

Hardware traces, such as instruction traces, can produce a vast amount of
trace data, so being able to reduce tracing to more specific circumstances
can be useful.

The ability to pause or resume tracing when another event happens, can do
that.

These patches add such a facilty and show how it would work for Intel
Processor Trace.

Maintainers of other AUX area tracing implementations are requested to
consider if this is something they might employ and then whether or not
the ABI would work for them. Note, thank you to James Clark (ARM) for
evaluating the API for Coresight. Suzuki K Poulose (ARM) also responded
positively to the RFC.

Changes to perf tools are now (since V4) fleshed out.

Please note, Intel® Architecture Instruction Set Extensions and Future
Features Programming Reference March 2024 319433-052, currently:

https://cdrdv2.intel.com/v1/dl/getContent/671368

introduces hardware pause / resume for Intel PT in a feature named
Intel PT Trigger Tracing.

For that more fields in perf_event_attr will be necessary. The main
differences are:
- it can be applied not just to overflows, but optionally to
every event
- a packet is emitted into the trace, optionally with IP
information
- no PMI
- works with PMC and DR (breakpoint) events only

Here are the proposed additions to perf_event_attr, please comment:

diff --git a/tools/include/uapi/linux/perf_event.h b/tools/include/uapi/linux/perf_event.h
index 0c557f0a17b3..05dcc43f11bb 100644
--- a/tools/include/uapi/linux/perf_event.h
+++ b/tools/include/uapi/linux/perf_event.h
@@ -369,6 +369,22 @@ enum perf_event_read_format {
PERF_FORMAT_MAX = 1U << 5, /* non-ABI */
};

+enum {
+ PERF_AUX_ACTION_START_PAUSED = 1U << 0,
+ PERF_AUX_ACTION_PAUSE = 1U << 1,
+ PERF_AUX_ACTION_RESUME = 1U << 2,
+ PERF_AUX_ACTION_EMIT = 1U << 3,
+ PERF_AUX_ACTION_NR = 0x1f << 4,
+ PERF_AUX_ACTION_NO_IP = 1U << 9,
+ PERF_AUX_ACTION_PAUSE_ON_EVT = 1U << 10,
+ PERF_AUX_ACTION_RESUME_ON_EVT = 1U << 11,
+ PERF_AUX_ACTION_EMIT_ON_EVT = 1U << 12,
+ PERF_AUX_ACTION_NR_ON_EVT = 0x1f << 13,
+ PERF_AUX_ACTION_NO_IP_ON_EVT = 1U << 18,
+ PERF_AUX_ACTION_MASK = ~PERF_AUX_ACTION_START_PAUSED,
+ PERF_AUX_PAUSE_RESUME_MASK = PERF_AUX_ACTION_PAUSE | PERF_AUX_ACTION_RESUME,
+};
+
#define PERF_ATTR_SIZE_VER0 64 /* sizeof first published struct */
#define PERF_ATTR_SIZE_VER1 72 /* add: config2 */
#define PERF_ATTR_SIZE_VER2 80 /* add: branch_sample_type */
@@ -515,10 +531,19 @@ struct perf_event_attr {
union {
__u32 aux_action;
struct {
- __u32 aux_start_paused : 1, /* start AUX area tracing paused */
- aux_pause : 1, /* on overflow, pause AUX area tracing */
- aux_resume : 1, /* on overflow, resume AUX area tracing */
- __reserved_3 : 29;
+ __u32 aux_start_paused : 1, /* start AUX area tracing paused */
+ aux_pause : 1, /* on overflow, pause AUX area tracing */
+ aux_resume : 1, /* on overflow, resume AUX area tracing */
+ aux_emit : 1, /* generate AUX records instead of events */
+ aux_nr : 5, /* AUX area tracing reference number */
+ aux_no_ip : 1, /* suppress IP in AUX records */
+ /* Following apply to event occurrence not overflows */
+ aux_pause_on_evt : 1, /* on event, pause AUX area tracing */
+ aux_resume_on_evt : 1, /* on event, resume AUX area tracing */
+ aux_emit_on_evt : 1, /* generate AUX records instead of events */
+ aux_nr_on_evt : 5, /* AUX area tracing reference number */
+ aux_no_ip_on_evt : 1, /* suppress IP in AUX records */
+ __reserved_3 : 13;
};
};

Changes in V13:
perf/core: Add aux_pause, aux_resume, aux_start_paused
Do aux_resume at the end of __perf_event_overflow() so as to trace
less of perf itself

perf tools: Add missing_features for aux_start_paused, aux_pause, aux_resume
Add error message also in EOPNOTSUPP case (Leo)

Changes in V12:
Add previously sent patch "perf/x86/intel/pt: Fix buffer full
but size is 0 case"

Add previously sent patch set "KVM: x86: Fix Intel PT Host/Guest
mode when host tracing"

Rebase on current tip plus patch set "KVM: x86: Fix Intel PT Host/Guest
mode when host tracing"

Changes in V11:
perf/core: Add aux_pause, aux_resume, aux_start_paused
Make assignment to event->hw.aux_paused conditional on
(pmu->capabilities & PERF_PMU_CAP_AUX_PAUSE).

perf/x86/intel: Do not enable large PEBS for events with aux actions or aux sampling
Remove definition of has_aux_action() because it has
already been added as an inline function.

perf/x86/intel/pt: Fix sampling synchronization
perf tools: Enable evsel__is_aux_event() to work for ARM/ARM64
perf tools: Enable evsel__is_aux_event() to work for S390_CPUMSF
Dropped because they have already been applied

Changes in V10:
perf/core: Add aux_pause, aux_resume, aux_start_paused
Move aux_paused into a union within struct hw_perf_event.
Additional comment wrt PERF_EF_PAUSE/PERF_EF_RESUME.
Factor out has_aux_action() as an inline function.
Use scoped_guard for irqsave.
Move calls of perf_event_aux_pause() from __perf_event_output()
to __perf_event_overflow().

Changes in V9:
perf/x86/intel/pt: Fix sampling synchronization
New patch

perf/core: Add aux_pause, aux_resume, aux_start_paused
Move aux_paused to struct hw_perf_event

perf/x86/intel/pt: Add support for pause / resume
Add more comments and barriers for resume_allowed and
pause_allowed
Always use WRITE_ONCE with resume_allowed

Changes in V8:

perf tools: Parse aux-action
Fix clang warning:
util/auxtrace.c:821:7: error: missing field 'aux_action' initializer [-Werror,-Wmissing-field-initializers]
821 | {NULL},
| ^

Changes in V7:

Add Andi's Reviewed-by for patches 2-12
Re-base

Changes in V6:

perf/core: Add aux_pause, aux_resume, aux_start_paused
Removed READ/WRITE_ONCE from __perf_event_aux_pause()
Expanded comment about guarding against NMI

Changes in V5:

perf/core: Add aux_pause, aux_resume, aux_start_paused
Added James' Ack

perf/x86/intel: Do not enable large PEBS for events with aux actions or aux sampling
New patch

perf tools
Added Ian's Ack

Changes in V4:

perf/core: Add aux_pause, aux_resume, aux_start_paused
Rename aux_output_cfg -> aux_action
Reorder aux_action bits from:
aux_pause, aux_resume, aux_start_paused
to:
aux_start_paused, aux_pause, aux_resume
Fix aux_action bits __u64 -> __u32

coresight: Have a stab at support for pause / resume
Dropped

perf tools
All new patches

Changes in RFC V3:

coresight: Have a stab at support for pause / resume
'mode' -> 'flags' so it at least compiles

Changes in RFC V2:

Use ->stop() / ->start() instead of ->pause_resume()
Move aux_start_paused bit into aux_output_cfg
Tighten up when Intel PT pause / resume is allowed
Add an example of how it might work for CoreSight

Adrian Hunter (14):
perf/x86/intel/pt: Fix buffer full but size is 0 case
KVM: x86: Fix Intel PT IA32_RTIT_CTL MSR validation
KVM: x86: Fix Intel PT Host/Guest mode when host tracing also
KVM: selftests: Add guest Intel PT test
perf/core: Add aux_pause, aux_resume, aux_start_paused
perf/x86/intel/pt: Add support for pause / resume
perf/x86/intel: Do not enable large PEBS for events with aux actions or aux sampling
perf tools: Add aux_start_paused, aux_pause and aux_resume
perf tools: Add aux-action config term
perf tools: Parse aux-action
perf tools: Add missing_features for aux_start_paused, aux_pause, aux_resume
perf intel-pt: Improve man page format
perf intel-pt: Add documentation for pause / resume
perf intel-pt: Add a test for pause / resume

arch/x86/events/intel/core.c | 4 +-
arch/x86/events/intel/pt.c | 209 +++++++-
arch/x86/events/intel/pt.h | 16 +
arch/x86/include/asm/intel_pt.h | 4 +
arch/x86/kvm/vmx/vmx.c | 26 +-
arch/x86/kvm/vmx/vmx.h | 1 -
include/linux/perf_event.h | 28 +
include/uapi/linux/perf_event.h | 11 +-
kernel/events/core.c | 75 ++-
kernel/events/internal.h | 1 +
tools/include/uapi/linux/perf_event.h | 11 +-
tools/perf/Documentation/perf-intel-pt.txt | 596 +++++++++++++--------
tools/perf/Documentation/perf-record.txt | 4 +
tools/perf/builtin-record.c | 4 +-
tools/perf/tests/shell/test_intel_pt.sh | 28 +
tools/perf/util/auxtrace.c | 67 ++-
tools/perf/util/auxtrace.h | 6 +-
tools/perf/util/evsel.c | 15 +
tools/perf/util/evsel.h | 1 +
tools/perf/util/evsel_config.h | 1 +
tools/perf/util/parse-events.c | 10 +
tools/perf/util/parse-events.h | 1 +
tools/perf/util/parse-events.l | 1 +
tools/perf/util/perf_event_attr_fprintf.c | 3 +
tools/perf/util/pmu.c | 1 +
tools/testing/selftests/kvm/Makefile | 1 +
.../selftests/kvm/include/x86_64/processor.h | 1 +
tools/testing/selftests/kvm/x86_64/intel_pt.c | 381 +++++++++++++
28 files changed, 1243 insertions(+), 264 deletions(-)
create mode 100644 tools/testing/selftests/kvm/x86_64/intel_pt.c

Regards
Adrian