Re: [RFC/PATCH 0/5] perf: Relax privilege restriction on AMD IBS (v3)

[Namhyung Kim]

On Wed, Sep 04, 2024 at 08:10:22PM -0700, Namhyung Kim wrote:
> Hello,
> 
> This is RFC v3 to allow AMD IBS to regular users on the default settings
> where kernel-level profiling is disabled (perf_event_paranoid=2).
> Currently AMD IBS doesn't allow any kind of exclusion in the event
> attribute.  But users needs to set attr.exclude_kernel to open an event
> on such an environment.
> 
> v3 changes)
> 
> * fix build on s390
> * add swfilt format for attr.config2
> * count powerpc core-book3s dropped samples
> 
> v2) https://lore.kernel.org/lkml/20240830232910.1839548-1-namhyung@xxxxxxxxxx/
> 
> * add PERF_FORMAT_DROPPED
> * account dropped sw events and from BPF handler
> * use precise RIP from IBS record
> 
> v1) https://lore.kernel.org/lkml/20240822230816.564262-1-namhyung@xxxxxxxxxx/
> 
> While IBS doesn't support hardware level privilege filters, the kernel
> can allow the event and drop samples belongs to the kernel like in the
> software events.  This is limited but it still contains precise samples
> which is important for various analysis like data type profiling.
> 
> This version added format/swfilt file in sysfs to expose the software
> filtering by setting the attribute config2 value.  I think it's easier
> to add a new config rather than adding a new PMU in order to handle
> event multiplexing across IBS PMU.  Users can use the perf tool to
> enable this feature manually like below.  Probably the perf tool can
> handle this automatically in the future.
> 
>   $ perf record -e ibs_op/swfilt=1/uh $PROG
> 
> (Not sure if it's better to accept or ignore exclude_hv so that it can
> use ":u" modifier only.)
> 
> In order to count those dropped samples correctly, I'd propose a new
> read format PERF_FORMAT_DROPPED same as we did for the lost samples.
> With this, it can count dropped samples in the software events and
> from the BPF overflow handler as well.
> 
> Let me know what you think.

Hi Peter and Ingo,

can I get your opinion on this?

Thanks,
Namhyung

> 
> Namhyung Kim (5):
>   perf/core: Add PERF_FORMAT_DROPPED
>   perf/core: Export perf_exclude_event()
>   perf/core: Account dropped samples from BPF
>   perf/powerpc: Count dropped samples in core-book3s PMU
>   perf/x86: Relax privilege filter restriction on AMD IBS
> 
>  arch/powerpc/perf/core-book3s.c |  4 ++-
>  arch/s390/kernel/perf_cpum_sf.c |  8 ++++--
>  arch/x86/events/amd/ibs.c       | 50 ++++++++++++++++++++++++---------
>  include/linux/perf_event.h      |  7 +++++
>  include/uapi/linux/perf_event.h |  5 +++-
>  kernel/events/core.c            | 27 ++++++++++++++----
>  6 files changed, 77 insertions(+), 24 deletions(-)
> 
> -- 
> 2.46.0.469.g59c65b2a67-goog
>