linux-kernel - [tip: perf/urgent] perf/x86/amd/ibs: Work around erratum #1197

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Date:   Thu, 26 Aug 2021 07:45:26 -0000
From:   "tip-bot2 for Kim Phillips" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Kim Phillips <kim.phillips@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: perf/urgent] perf/x86/amd/ibs: Work around erratum #1197

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

Commit-ID:     26db2e0c51fe83e1dd852c1321407835b481806e
Gitweb:        https://git.kernel.org/tip/26db2e0c51fe83e1dd852c1321407835b481806e
Author:        Kim Phillips <kim.phillips@....com>
AuthorDate:    Tue, 17 Aug 2021 17:10:42 -05:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Thu, 26 Aug 2021 08:58:02 +02:00

perf/x86/amd/ibs: Work around erratum #1197

Erratum #1197 "IBS (Instruction Based Sampling) Register State May be
Incorrect After Restore From CC6" is published in a document:

  "Revision Guide for AMD Family 19h Models 00h-0Fh Processors" 56683 Rev. 1.04 July 2021

  https://bugzilla.kernel.org/show_bug.cgi?id=206537

Implement the erratum's suggested workaround and ignore IBS samples if
MSRC001_1031 == 0.

Signed-off-by: Kim Phillips <kim.phillips@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Link: https://lore.kernel.org/r/20210817221048.88063-3-kim.phillips@amd.com
---
 arch/x86/events/amd/ibs.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
index 40669ea..921f47b 100644
--- a/arch/x86/events/amd/ibs.c
+++ b/arch/x86/events/amd/ibs.c
@@ -90,6 +90,7 @@ struct perf_ibs {
 	unsigned long			offset_mask[1];
 	int				offset_max;
 	unsigned int			fetch_count_reset_broken : 1;
+	unsigned int			fetch_ignore_if_zero_rip : 1;
 	struct cpu_perf_ibs __percpu	*pcpu;
 
 	struct attribute		**format_attrs;
@@ -672,6 +673,10 @@ fail:
 	if (check_rip && (ibs_data.regs[2] & IBS_RIP_INVALID)) {
 		regs.flags &= ~PERF_EFLAGS_EXACT;
 	} else {
+		/* Workaround for erratum #1197 */
+		if (perf_ibs->fetch_ignore_if_zero_rip && !(ibs_data.regs[1]))
+			goto out;
+
 		set_linear_ip(&regs, ibs_data.regs[1]);
 		regs.flags |= PERF_EFLAGS_EXACT;
 	}
@@ -769,6 +774,9 @@ static __init void perf_event_ibs_init(void)
 	if (boot_cpu_data.x86 >= 0x16 && boot_cpu_data.x86 <= 0x18)
 		perf_ibs_fetch.fetch_count_reset_broken = 1;
 
+	if (boot_cpu_data.x86 == 0x19 && boot_cpu_data.x86_model < 0x10)
+		perf_ibs_fetch.fetch_ignore_if_zero_rip = 1;
+
 	perf_ibs_pmu_init(&perf_ibs_fetch, "ibs_fetch");
 
 	if (ibs_caps & IBS_CAPS_OPCNT) {