linux-kernel - [tip: perf/core] perf/amd/ibs: Use interrupt regs ip for stack unwinding

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Date:   Tue, 10 May 2022 09:11:38 -0000
From:   "tip-bot2 for Ravi Bangoria" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>,
        Peter Zijlstra <peterz@...radead.org>,
        Ravi Bangoria <ravi.bangoria@....com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: perf/core] perf/amd/ibs: Use interrupt regs ip for stack unwinding

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     3d47083b9ff46863e8374ad3bb5edb5e464c75f8
Gitweb:        https://git.kernel.org/tip/3d47083b9ff46863e8374ad3bb5edb5e464c75f8
Author:        Ravi Bangoria <ravi.bangoria@....com>
AuthorDate:    Fri, 29 Apr 2022 10:44:41 +05:30
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 10 May 2022 11:00:45 +02:00

perf/amd/ibs: Use interrupt regs ip for stack unwinding

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@...dex-team.ru>
Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Ravi Bangoria <ravi.bangoria@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20220429051441.14251-1-ravi.bangoria@amd.com
---
 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 9739019..11e8b49 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 @@ fail:
 		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) {