Re: [PATCH 12/12] perf mem record: Use the IBS swfilt filter when available

[Namhyung Kim <namhyung@kernel.org>]

+Ravi

On Wed, Sep 16, 2026 at 08:47:39AM -0300, Arnaldo Carvalho de Melo wrote:
> From: Arnaldo Carvalho de Melo <acme@redhat.com>
> 
> IBS events with exclude_{user,kernel} bits, as used in per-thread mode
> when kernel samples are not allowed, are rejected by the kernel on
> hardware without the privilege filter, so a per-thread 'perf mem
> record' fails:
> 
>   $ perf mem record -o /dev/null -- true
>   Error:
>   Failure to open event 'ibs_op/ldlat=0/u' on PMU 'ibs_op' which will be removed.
>   Invalid event (ibs_op/ldlat=0/u) in per-thread mode, enable system wide with '-a'.
> 
> Kernel v6.14 added swfilt, a software privilege filter that makes those
> events usable per-thread, exposed as the 'swfilt' format term
> (d29e744c71673a71 "perf/x86: Relax privilege filter restriction on AMD
> IBS"):
> 
>   $ perf record -e ibs_op/ldlat=0,swfilt=1/ -- true
> 
> Give the ibs_op memory events a name variant with the swfilt term, used
> when the PMU exposes it as a format term, keeping the names that need
> system wide mode otherwise.
> 
> The variant is used even for records that end up without exclude bits,
> e.g. a plain system wide one: perf record adds those bits itself when
> the first open fails with EACCES on an unprivileged setup, after the
> event name has been built, so the term has to be in it for that retry:
> 
>   $ perf record -v -e ibs_op/ldlat=0/ -- true
>   kernel.perf_event_paranoid=2, trying to fall back to excluding kernel and hypervisor  samples
>   Failure to open event 'ibs_op/ldlat=0/u' on PMU 'ibs_op' which will be removed.
>   Invalid event (ibs_op/ldlat=0/u) in per-thread mode, enable system wide with '-a'.
> 
> With no exclude bits the kernel discards nothing.
> 
> This makes the per-thread 'perf mem record' that the data type profiling
> shell test does work: the skip added by patch 1 is driven by that record
> failing, so it now runs on AMD kernels with swfilt, and keeps skipping on
> kernels without it.  The 'Test data symbol' shell test matches the exact
> ibs_op event string, so its regex now accepts terms added after
> ldlat=150, and it only checks ldlat when the captured term has it: on
> uarch without ldlat the swfilt variant makes the capture non-empty
> ("swfilt=1"), that the old 'ldlat=0' check would reject.
> 
> Suggested-by: Namhyung Kim <namhyung@kernel.org>
> Assisted-by: LLM
> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> ---
>  tools/perf/arch/x86/util/mem-events.c      | 17 ++++++++++++++---
>  tools/perf/tests/shell/test_data_symbol.sh |  6 ++++--
>  tools/perf/util/mem-events.c               | 21 +++++++++++++++++----
>  tools/perf/util/mem-events.h               |  2 ++
>  4 files changed, 37 insertions(+), 9 deletions(-)
> 
> diff --git a/tools/perf/arch/x86/util/mem-events.c b/tools/perf/arch/x86/util/mem-events.c
> index b38f519020ff8c6f..034053dc762101dc 100644
> --- a/tools/perf/arch/x86/util/mem-events.c
> +++ b/tools/perf/arch/x86/util/mem-events.c
> @@ -7,7 +7,10 @@
>  
>  #define MEM_LOADS_AUX		0x8203
>  
> -#define E(t, n, s, l, a) { .tag = t, .name = n, .event_name = s, .ldlat = l, .aux_event = a }
> +#define E_INIT(t, n, s, l, a, sf) {					\
> +	.tag = t, .name = n, .event_name = s, .swfilt_name = sf,	\
> +	.ldlat = l, .aux_event = a }
> +#define E(t, n, s, l, a) E_INIT(t, n, s, l, a, NULL)
>  
>  struct perf_mem_event perf_mem_events_intel[PERF_MEM_EVENTS__MAX] = {
>  	E("ldlat-loads",	"%s/mem-loads,ldlat=%u/P",	"mem-loads",	true,	0),
> @@ -21,14 +24,22 @@ struct perf_mem_event perf_mem_events_intel_aux[PERF_MEM_EVENTS__MAX] = {
>  	E(NULL,			NULL,				NULL,		false,	0),
>  };
>  
> +/*
> + * IBS events with exclude_{user,kernel} bits set, as used by perf to
> + * record per-thread when kernel samples are not allowed, are rejected
> + * by the kernel on hardware without the privilege filter unless the
> + * swfilt software filter is used, so these events carry a variant of
> + * their names with the swfilt term, used by perf_pmu__mem_events_name()
> + * when the kernel exposes the term.
> + */
>  struct perf_mem_event perf_mem_events_amd[PERF_MEM_EVENTS__MAX] = {
>  	E(NULL,		NULL,		NULL,	false,	0),
>  	E(NULL,		NULL,		NULL,	false,	0),
> -	E("mem-ldst",	"%s//",		NULL,	false,	0),
> +	E_INIT("mem-ldst",	"%s//",		NULL,	false,	0, "%s/swfilt=1/"),
>  };
>  
>  struct perf_mem_event perf_mem_events_amd_ldlat[PERF_MEM_EVENTS__MAX] = {
>  	E(NULL,		NULL,		NULL,	false,	0),
>  	E(NULL,		NULL,		NULL,	false,	0),
> -	E("mem-ldst",	"%s/ldlat=%u/",	NULL,	true,	0),
> +	E_INIT("mem-ldst",	"%s/ldlat=%u/",	NULL,	true,	0, "%s/ldlat=%u,swfilt=1/"),
>  };
> diff --git a/tools/perf/tests/shell/test_data_symbol.sh b/tools/perf/tests/shell/test_data_symbol.sh
> index d61b5659a46d9a77..52c837fddb639595 100755
> --- a/tools/perf/tests/shell/test_data_symbol.sh
> +++ b/tools/perf/tests/shell/test_data_symbol.sh
> @@ -65,15 +65,17 @@ if (($is_amd >= 1)); then
>  	# --ldlat on AMD:
>  	# o Zen4 and earlier uarch does not support ldlat
>  	# o Even on supported platforms, it's disabled (--ldlat=0) by default.
> +	# o Kernels with the swfilt term add it even when ldlat is not
> +	#   supported, so only check ldlat when the term is present.
>  	ldlat=${BASH_REMATCH[1]}
> -	if [[ -n $ldlat ]]; then
> +	if [[ $ldlat == *ldlat=* ]]; then
>  		if ! [[ "$ldlat" =~ ldlat=0 ]]; then
>  			echo "ERROR: ldlat not initialized to 0?"
>  			exit 1
>  		fi
>  
>  		mem_events="$(perf mem record -v --ldlat=150 -e list 2>&1)"
> -		if ! [[ "$mem_events" =~ ^mem-ldst.*ibs_op/ldlat=150/.*available ]]; then
> +		if ! [[ "$mem_events" =~ ^mem-ldst.*ibs_op/ldlat=150[,/].*available ]]; then
>  			echo "ERROR: --ldlat not honored?"
>  			exit 1
>  		fi
> diff --git a/tools/perf/util/mem-events.c b/tools/perf/util/mem-events.c
> index 0b49fce251fcc184..8f74cd085e500231 100644
> --- a/tools/perf/util/mem-events.c
> +++ b/tools/perf/util/mem-events.c
> @@ -82,6 +82,7 @@ static const char *perf_pmu__mem_events_name(struct perf_pmu *pmu, int i,
>  					     char *buf, size_t buf_size)
>  {
>  	struct perf_mem_event *e;
> +	const char *name;
>  
>  	if (i >= PERF_MEM_EVENTS__MAX || !pmu)
>  		return NULL;
> @@ -90,24 +91,36 @@ static const char *perf_pmu__mem_events_name(struct perf_pmu *pmu, int i,
>  	if (!e || !e->name)
>  		return NULL;
>  
> +	/*
> +	 * Use the swfilt variant of the name when the PMU exposes the term.
> +	 * It is not conditional on the event already having exclude bits:
> +	 * perf record adds those bits itself when the first open fails with
> +	 * EACCES on an unprivileged setup, after this name has been built,
> +	 * and that retry only succeeds with the term in the name.  With no
> +	 * exclude bits the kernel doesn't discard anything.
> +	 */
> +	name = e->name;
> +	if (e->swfilt_name && perf_pmu__has_format(pmu, "swfilt"))
> +		name = e->swfilt_name;

It's a bit unfortunate we hardcode "swfilt" here.  Probably better to
have it in the mem-events array and add it to the name format
dynamically.  But as it's only needed for IBS, I think it's ok for now.

Thanks,
Namhyung

> +
>  	if (i == PERF_MEM_EVENTS__LOAD || i == PERF_MEM_EVENTS__LOAD_STORE) {
>  		if (e->ldlat) {
>  			if (!e->aux_event) {
>  				/* ARM and Most of Intel */
>  				scnprintf(buf, buf_size,
> -					  e->name, pmu->name,
> +					  name, pmu->name,
>  					  perf_mem_events__loads_ldlat);
>  			} else {
>  				/* Intel with mem-loads-aux event */
>  				scnprintf(buf, buf_size,
> -					  e->name, pmu->name, pmu->name,
> +					  name, pmu->name, pmu->name,
>  					  perf_mem_events__loads_ldlat);
>  			}
>  		} else {
>  			if (!e->aux_event) {
>  				/* AMD and POWER */
>  				scnprintf(buf, buf_size,
> -					  e->name, pmu->name);
> +					  name, pmu->name);
>  			} else {
>  				return NULL;
>  			}
> @@ -117,7 +130,7 @@ static const char *perf_pmu__mem_events_name(struct perf_pmu *pmu, int i,
>  
>  	if (i == PERF_MEM_EVENTS__STORE) {
>  		scnprintf(buf, buf_size,
> -			  e->name, pmu->name);
> +			  name, pmu->name);
>  		return buf;
>  	}
>  
> diff --git a/tools/perf/util/mem-events.h b/tools/perf/util/mem-events.h
> index 5b98076904b0b689..41f628fad10709b9 100644
> --- a/tools/perf/util/mem-events.h
> +++ b/tools/perf/util/mem-events.h
> @@ -11,6 +11,8 @@ struct perf_mem_event {
>  	u32		aux_event;
>  	const char	*tag;
>  	const char	*name;
> +	/* Name with the swfilt software privilege filter, when supported. */
> +	const char	*swfilt_name;
>  	const char	*event_name;
>  };
>  
> -- 
> 2.55.0
>