linux-kernel - [tip: perf/urgent] perf/x86/intel/uncore: Fix a kernel WARNING triggered by maxcpus=1

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Date:   Mon, 31 May 2021 10:40:43 -0000
From:   "tip-bot2 for Kan Liang" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     John Donnelly <john.p.donnelly@...cle.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: perf/urgent] perf/x86/intel/uncore: Fix a kernel WARNING
 triggered by maxcpus=1

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

Commit-ID:     4a0e3ff30980b7601b13dd3b7ee275212b852843
Gitweb:        https://git.kernel.org/tip/4a0e3ff30980b7601b13dd3b7ee275212b852843
Author:        Kan Liang <kan.liang@...ux.intel.com>
AuthorDate:    Wed, 26 May 2021 06:58:47 -07:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Mon, 31 May 2021 10:14:51 +02:00

perf/x86/intel/uncore: Fix a kernel WARNING triggered by maxcpus=1

A kernel WARNING may be triggered when setting maxcpus=1.

The uncore counters are Die-scope. When probing a PCI device, only the
BUS information can be retrieved. The uncore driver has to maintain a
mapping table used to calculate the logical Die ID from a given BUS#.

Before the patch ba9506be4e40, the mapping table stores the mapping
information from the BUS# -> a Physical Socket ID. To calculate the
logical die ID, perf does,
- In snbep_pci2phy_map_init(), retrieve the BUS# -> a Physical Socket ID
  from the UBOX PCI configure space.
- Calculate the mapping information (a BUS# -> a Physical Socket ID) for
  the other PCI BUS.
- In the uncore_pci_probe(), get the physical Socket ID from a given BUS
  and the mapping table.
- Calculate the logical Die ID

Since only the logical Die ID is required, with the patch ba9506be4e40,
the mapping table stores the mapping information from the BUS# -> a
logical Die ID. Now perf does,
- In snbep_pci2phy_map_init(), retrieve the BUS# -> a Physical Socket ID
  from the UBOX PCI configure space.
- Calculate the logical Die ID
- Calculate the mapping information (a BUS# -> a logical Die ID) for the
  other PCI BUS.
- In the uncore_pci_probe(), get the logical die ID from a given BUS and
  the mapping table.

When calculating the logical Die ID, -1 may be returned, especially when
maxcpus=1. Here, -1 means the logical Die ID is not found. But when
calculating the mapping information for the other PCI BUS, -1 indicates
that it's the other PCI BUS that requires the calculation of the
mapping. The driver will mistakenly do the calculation.

Uses the -ENODEV to indicate the case which the logical Die ID is not
found. The driver will not mess up the mapping table anymore.

Fixes: ba9506be4e40 ("perf/x86/intel/uncore: Store the logical die id instead of the physical die id.")
Reported-by: John Donnelly <john.p.donnelly@...cle.com>
Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: John Donnelly <john.p.donnelly@...cle.com>
Tested-by: John Donnelly <john.p.donnelly@...cle.com>
Link: https://lkml.kernel.org/r/1622037527-156028-1-git-send-email-kan.liang@linux.intel.com
---
 arch/x86/events/intel/uncore_snbep.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/intel/uncore_snbep.c b/arch/x86/events/intel/uncore_snbep.c
index 63f0972..1587d32 100644
--- a/arch/x86/events/intel/uncore_snbep.c
+++ b/arch/x86/events/intel/uncore_snbep.c
@@ -1406,6 +1406,8 @@ static int snbep_pci2phy_map_init(int devid, int nodeid_loc, int idmap_loc, bool
 						die_id = i;
 					else
 						die_id = topology_phys_to_logical_pkg(i);
+					if (die_id < 0)
+						die_id = -ENODEV;
 					map->pbus_to_dieid[bus] = die_id;
 					break;
 				}
@@ -1452,14 +1454,14 @@ static int snbep_pci2phy_map_init(int devid, int nodeid_loc, int idmap_loc, bool
 			i = -1;
 			if (reverse) {
 				for (bus = 255; bus >= 0; bus--) {
-					if (map->pbus_to_dieid[bus] >= 0)
+					if (map->pbus_to_dieid[bus] != -1)
 						i = map->pbus_to_dieid[bus];
 					else
 						map->pbus_to_dieid[bus] = i;
 				}
 			} else {
 				for (bus = 0; bus <= 255; bus++) {
-					if (map->pbus_to_dieid[bus] >= 0)
+					if (map->pbus_to_dieid[bus] != -1)
 						i = map->pbus_to_dieid[bus];
 					else
 						map->pbus_to_dieid[bus] = i;