linux-kernel - [tip: perf/urgent] perf/x86/amd: Do not WARN() on every IRQ

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Message-ID: <169563484702.27769.17534862657597994839.tip-bot2@tip-bot2>
Date:   Mon, 25 Sep 2023 09:40:47 -0000
From:   "tip-bot2 for Breno Leitao" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Jirka Hladky <jhladky@...hat.com>,
        Breno Leitao <leitao@...ian.org>,
        Sandipan Das <sandipan.das@....com>,
        Ingo Molnar <mingo@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: perf/urgent] perf/x86/amd: Do not WARN() on every IRQ

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

Commit-ID:     599522d9d2e19d6240e4312577f1c5f3ffca22f6
Gitweb:        https://git.kernel.org/tip/599522d9d2e19d6240e4312577f1c5f3ffca22f6
Author:        Breno Leitao <leitao@...ian.org>
AuthorDate:    Thu, 14 Sep 2023 19:58:40 +05:30
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Mon, 25 Sep 2023 11:30:31 +02:00

perf/x86/amd: Do not WARN() on every IRQ

Zen 4 systems running buggy microcode can hit a WARN_ON() in the PMI
handler, as shown below, several times while perf runs. A simple
`perf top` run is enough to render the system unusable:

  WARNING: CPU: 18 PID: 20608 at arch/x86/events/amd/core.c:944 amd_pmu_v2_handle_irq+0x1be/0x2b0

This happens because the Performance Counter Global Status Register
(PerfCntGlobalStatus) has one or more bits set which are considered
reserved according to the "AMD64 Architecture Programmer’s Manual,
Volume 2: System Programming, 24593":

  https://www.amd.com/system/files/TechDocs/24593.pdf

To make this less intrusive, warn just once if any reserved bit is set
and prompt the user to update the microcode. Also sanitize the value to
what the code is handling, so that the overflow events continue to be
handled for the number of counters that are known to be sane.

Going forward, the following microcode patch levels are recommended
for Zen 4 processors in order to avoid such issues with reserved bits:

  Family=0x19 Model=0x11 Stepping=0x01: Patch=0x0a10113e
  Family=0x19 Model=0x11 Stepping=0x02: Patch=0x0a10123e
  Family=0x19 Model=0xa0 Stepping=0x01: Patch=0x0aa00116
  Family=0x19 Model=0xa0 Stepping=0x02: Patch=0x0aa00212

Commit f2eb058afc57 ("linux-firmware: Update AMD cpu microcode") from
the linux-firmware tree has binaries that meet the minimum required
patch levels.

  [ sandipan: - add message to prompt users to update microcode
              - rework commit message and call out required microcode levels ]

Fixes: 7685665c390d ("perf/x86/amd/core: Add PerfMonV2 overflow handling")
Reported-by: Jirka Hladky <jhladky@...hat.com>
Signed-off-by: Breno Leitao <leitao@...ian.org>
Signed-off-by: Sandipan Das <sandipan.das@....com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Link: https://lore.kernel.org/all/3540f985652f41041e54ee82aa53e7dbd55739ae.1694696888.git.sandipan.das@amd.com/
---
 arch/x86/events/amd/core.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
index ed626bf..e249765 100644
--- a/arch/x86/events/amd/core.c
+++ b/arch/x86/events/amd/core.c
@@ -886,7 +886,7 @@ static int amd_pmu_v2_handle_irq(struct pt_regs *regs)
 	struct hw_perf_event *hwc;
 	struct perf_event *event;
 	int handled = 0, idx;
-	u64 status, mask;
+	u64 reserved, status, mask;
 	bool pmu_enabled;
 
 	/*
@@ -911,6 +911,14 @@ static int amd_pmu_v2_handle_irq(struct pt_regs *regs)
 		status &= ~GLOBAL_STATUS_LBRS_FROZEN;
 	}
 
+	reserved = status & ~amd_pmu_global_cntr_mask;
+	if (reserved)
+		pr_warn_once("Reserved PerfCntrGlobalStatus bits are set (0x%llx), please consider updating microcode\n",
+			     reserved);
+
+	/* Clear any reserved bits set by buggy microcode */
+	status &= amd_pmu_global_cntr_mask;
+
 	for (idx = 0; idx < x86_pmu.num_counters; idx++) {
 		if (!test_bit(idx, cpuc->active_mask))
 			continue;