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Message-ID: <49fd4eb5-ee7b-45f5-a40f-dbfd793cdff4@amd.com>
Date: Tue, 15 Oct 2024 19:06:24 +0530
From: Ravi Bangoria <ravi.bangoria@....com>
To: Namhyung Kim <namhyung@...nel.org>, Peter Zijlstra
<peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>
Cc: Kan Liang <kan.liang@...ux.intel.com>, Mark Rutland
<mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
LKML <linux-kernel@...r.kernel.org>, Stephane Eranian <eranian@...gle.com>,
Ananth Narayan <ananth.narayan@....com>, Sandipan Das
<sandipan.das@....com>, Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH 5/5] perf/x86: Relax privilege filter restriction on AMD
IBS
Hi Namhyung,
On 05-Sep-24 8:40 AM, Namhyung Kim wrote:
> While IBS is available for per-thread profiling, still regular users
> cannot open an event due to the default paranoid setting (2) which
> doesn't allow unprivileged users to get kernel samples. That means
> it needs to set exclude_kernel bit in the attribute but IBS driver
> would reject it since it has PERF_PMU_CAP_NO_EXCLUDE. This is not what
> we want and I've been getting requests to fix this issue.
>
> This should be done in the hardware, but until we get the HW fix we may
> allow exclude_{kernel,user} in the attribute and silently drop the
> samples in the PMU IRQ handler. It won't guarantee the sampling
> frequency or even it'd miss some with fixed period too. Not ideal,
> but that'd still be helpful to regular users.
>
> To minimize the confusion, let's add 'swfilt' bit to attr.config2 which
> is exposed in the sysfs format directory so that users can figure out
> if the kernel support the privilege filters by software.
>
> $ perf record -e ibs_op/swfilt=1/uh true
Shall we add an example in tools/perf/Documentation/perf-amd-ibs.txt?
> +static struct attribute *swfilt_attrs[] = {
> + &format_attr_swfilt.attr,
> + NULL,
> +};
> +
> static struct attribute *fetch_l3missonly_attrs[] = {
> &fetch_l3missonly.attr.attr,
> NULL,
> @@ -598,6 +604,11 @@ static struct attribute_group group_rand_en = {
> .attrs = rand_en_attrs,
> };
>
> +static struct attribute_group group_swfilt = {
> + .name = "format",
> + .attrs = swfilt_attrs,
> +};
> +
> static struct attribute_group group_fetch_l3missonly = {
> .name = "format",
> .attrs = fetch_l3missonly_attrs,
> @@ -612,6 +623,7 @@ static struct attribute_group group_zen4_ibs_extensions = {
>
> static const struct attribute_group *fetch_attr_groups[] = {
> &group_rand_en,
> + &group_swfilt,
> &empty_caps_group,
> NULL,
> };
Causes:
# dmesg
sysfs: cannot create duplicate filename '/devices/ibs_fetch/format'
Failed to register pmu: ibs_fetch, reason -17
Rename rand_en_attrs[] to fetch_attrs[], add &format_attr_swfilt.attr
to it and remove &group_swfilt from fetch_attr_groups[]. And I guess
it should work.
Thanks,
Ravi
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