[tip: perf/core] perf/x86/intel/uncore: Fix discovery unit lookup for multi-die systems

[tip-bot2 for Zide Chen]

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

Commit-ID:     63f48abd55d0417996bca86022925c853a2b436b
Gitweb:        https://git.kernel.org/tip/63f48abd55d0417996bca86022925c853a2b436b
Author:        Zide Chen <zide.chen@xxxxxxxxx>
AuthorDate:    Tue, 02 Jun 2026 07:49:02 -07:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Thu, 04 Jun 2026 11:38:36 +02:00

perf/x86/intel/uncore: Fix discovery unit lookup for multi-die systems

In uncore_find_add_unit(), PMON units with the same unit ID may be
added to the uncore discovery RB-tree for different dies. These units
are distinguished by node->die.

However, intel_generic_uncore_box_ctl() uses a fixed die ID of -1 when
looking up the discovery unit, which may retrieve the wrong node on
multi-die systems.

Use box->dieid instead so the correct discovery unit is selected.

No functional issue has been observed so far because currently supported
platforms happen to use the same unit control register for such units.

Remove WARN_ON_ONCE() because with the above change a NULL unit can be
expected, e.g. when a CPU die is offline during uncore enumeration and
the unit is not added to the RB-tree. In this case,
intel_uncore_find_discovery_unit() returns NULL once the die becomes
online, and it is expected that the PMU box is not functional for that
die.

Fixes: b1d9ea2e1ca4 ("perf/x86/uncore: Apply the unit control RB tree to MSR uncore units")
Signed-off-by: Zide Chen <zide.chen@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
Link: https://patch.msgid.link/20260602144908.263680-2-zide.chen@xxxxxxxxx
---
 arch/x86/events/intel/uncore_discovery.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/intel/uncore_discovery.c b/arch/x86/events/intel/uncore_discovery.c
index 583cbd0..60e1200 100644
--- a/arch/x86/events/intel/uncore_discovery.c
+++ b/arch/x86/events/intel/uncore_discovery.c
@@ -481,8 +481,8 @@ static u64 intel_generic_uncore_box_ctl(struct intel_uncore_box *box)
 	struct intel_uncore_discovery_unit *unit;
 
 	unit = intel_uncore_find_discovery_unit(box->pmu->type->boxes,
-						-1, box->pmu->pmu_idx);
-	if (WARN_ON_ONCE(!unit))
+						box->dieid, box->pmu->pmu_idx);
+	if (!unit)
 		return 0;
 
 	return unit->addr;