Re: [tip:perf/urgent] perf/x86/intel: Fix INTEL_FLAGS_EVENT_CONSTRAINT* masking

[Ingo Molnar <mingo@kernel.org>]

* tip-bot for Stephane Eranian <tipbot@zytor.com> wrote:

> Commit-ID:  6b89d4c1ae8596a8c9240f169ef108704de373f2
> Gitweb:     https://git.kernel.org/tip/6b89d4c1ae8596a8c9240f169ef108704de373f2
> Author:     Stephane Eranian <eranian@google.com>
> AuthorDate: Thu, 9 May 2019 14:45:56 -0700
> Committer:  Ingo Molnar <mingo@kernel.org>
> CommitDate: Fri, 10 May 2019 08:04:17 +0200
> 
> perf/x86/intel: Fix INTEL_FLAGS_EVENT_CONSTRAINT* masking
> 
> On Intel Westmere, a cmdline as follows:
> 
>   $ perf record -e cpu/event=0xc4,umask=0x2,name=br_inst_retired.near_call/p ....
> 
> was failing. Yet the event+ umask support PEBS.
> 
> It turns out this is due to a bug in the the PEBS event constraint table for
> westmere. All forms of BR_INST_RETIRED.* support PEBS. Therefore the constraint
> mask should ignore the umask. The name of the macro INTEL_FLAGS_EVENT_CONSTRAINT()
> hint that this is the case but it was not. That macros was checking both the
> event code and event umask. Therefore, it was only matching on 0x00c4.
> There are code+umask macros, they all have *UEVENT*.
> 
> This bug fixes the issue by checking only the event code in the mask.
> Both single and range version are modified.
> 
> Signed-off-by: Stephane Eranian <eranian@google.com>
> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Cc: Jiri Olsa <jolsa@redhat.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Vince Weaver <vincent.weaver@maine.edu>
> Cc: kan.liang@intel.com
> Link: http://lkml.kernel.org/r/20190509214556.123493-1-eranian@google.com
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> ---
>  arch/x86/events/perf_event.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
> index 07fc84bb85c1..a6ac2f4f76fc 100644
> --- a/arch/x86/events/perf_event.h
> +++ b/arch/x86/events/perf_event.h
> @@ -394,10 +394,10 @@ struct cpu_hw_events {
>  
>  /* Event constraint, but match on all event flags too. */
>  #define INTEL_FLAGS_EVENT_CONSTRAINT(c, n) \
> -	EVENT_CONSTRAINT(c, n, INTEL_ARCH_EVENT_MASK|X86_ALL_EVENT_FLAGS)
> +	EVENT_CONSTRAINT(c, n, ARCH_PERFMON_EVENTSEL_EVENT|X86_ALL_EVENT_FLAGS)
>  
>  #define INTEL_FLAGS_EVENT_CONSTRAINT_RANGE(c, e, n)			\
> -	EVENT_CONSTRAINT_RANGE(c, e, n, INTEL_ARCH_EVENT_MASK|X86_ALL_EVENT_FLAGS)
> +	EVENT_CONSTRAINT_RANGE(c, e, n, ARCH_PERFMON_EVENTSEL_EVENT|X86_ALL_EVENT_FLAGS)

This commit broke one of my testboxes - and unfortunately I noticed this 
too late and the commit is now upstream.

The breakage is that 'perf top' stops working altogether, it errors out 
in the event creation:

 $ perf top --stdio
 Error:
 The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (cycles).

I bisected it back to this commit:

 6b89d4c1ae8596a8c9240f169ef108704de373f2 is the first bad commit
 commit 6b89d4c1ae8596a8c9240f169ef108704de373f2
 Author: Stephane Eranian <eranian@google.com>
 Date:   Thu May 9 14:45:56 2019 -0700

    perf/x86/intel: Fix INTEL_FLAGS_EVENT_CONSTRAINT* masking

The system is IvyBridge model 62, running a defconfig-ish kernel, and 
with perf_event_paranoid set to -1:

 [    3.756600] Performance Events: PEBS fmt1+, IvyBridge events, 16-deep LBR, full-width counters, Intel PMU driver.

 processor	: 39
 vendor_id	: GenuineIntel
 cpu family	: 6
 model		: 62
 model name	: Intel(R) Xeon(R) CPU E5-2680 v2 @ 2.80GHz
 stepping	: 4
 microcode	: 0x428

If I revert the commit 'perf top' starts working again.

Thanks,

	Ingo