Re: [PATCH] perf/amd/ibs: Use interrupt regs ip for stack unwinding

From: Namhyung Kim <namhyung@kernel.org>
To: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Ingo Molnar <mingo@redhat.com>,
	Mark Rutland <mark.rutland@arm.com>, Jiri Olsa <jolsa@kernel.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Borislav Petkov <bp@alien8.de>,
	dave.hansen@linux.intel.com, "H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org,
	linux-perf-users <linux-perf-users@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	sandipan.das@amd.com, ananth.narayan@amd.com,
	Kim Phillips <kim.phillips@amd.com>,
	santosh.shukla@amd.com, Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH] perf/amd/ibs: Use interrupt regs ip for stack unwinding
Date: Sun, 1 May 2022 23:07:14 -0700	[thread overview]
Message-ID: <CAM9d7cjksVPHYJEjqckotqzC62dBNW9frsMQaBECngMopU4znw@mail.gmail.com> (raw)
In-Reply-To: <20220429051441.14251-1-ravi.bangoria@amd.com>

Hello,

On Thu, Apr 28, 2022 at 10:15 PM Ravi Bangoria <ravi.bangoria@amd.com> wrote:
>
> IbsOpRip is recorded when IBS interrupt is triggered. But there is
> a skid from the time IBS interrupt gets triggered to the time the
> interrupt is presented to the core. Meanwhile processor would have
> moved ahead and thus IbsOpRip will be inconsistent with rsp and rbp
> recorded as part of the interrupt regs. This causes issues while
> unwinding stack using the ORC unwinder as it needs consistent rip,
> rsp and rbp. Fix this by using rip from interrupt regs instead of
> IbsOpRip for stack unwinding.
>
> Fixes: ee9f8fce99640 ("x86/unwind: Add the ORC unwinder")
> Reported-by: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>

Acked-by: Namhyung Kim <namhyung@kernel.org>

Thanks,
Namhyung


> ---
>  arch/x86/events/amd/ibs.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
> index 9739019d4b67..171941043f53 100644
> --- a/arch/x86/events/amd/ibs.c
> +++ b/arch/x86/events/amd/ibs.c
> @@ -304,6 +304,16 @@ static int perf_ibs_init(struct perf_event *event)
>         hwc->config_base = perf_ibs->msr;
>         hwc->config = config;
>
> +       /*
> +        * rip recorded by IbsOpRip will not be consistent with rsp and rbp
> +        * recorded as part of interrupt regs. Thus we need to use rip from
> +        * interrupt regs while unwinding call stack. Setting _EARLY flag
> +        * makes sure we unwind call-stack before perf sample rip is set to
> +        * IbsOpRip.
> +        */
> +       if (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN)
> +               event->attr.sample_type |= __PERF_SAMPLE_CALLCHAIN_EARLY;
> +
>         return 0;
>  }
>
> @@ -687,6 +697,14 @@ static int perf_ibs_handle_irq(struct perf_ibs *perf_ibs, struct pt_regs *iregs)
>                 data.raw = &raw;
>         }
>
> +       /*
> +        * rip recorded by IbsOpRip will not be consistent with rsp and rbp
> +        * recorded as part of interrupt regs. Thus we need to use rip from
> +        * interrupt regs while unwinding call stack.
> +        */
> +       if (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN)
> +               data.callchain = perf_callchain(event, iregs);
> +
>         throttle = perf_event_overflow(event, &data, &regs);
>  out:
>         if (throttle) {
> --
> 2.27.0
>