linux-kernel - Re: [PATCH 1/2] perf/x86/intel/uncore: Skip discovery table for offline dies

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Message-ID: <2d5456ec-b799-4a90-ac7a-f49deafa110d@linux.intel.com>
Date: Thu, 30 Oct 2025 14:23:09 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: "Chen, Zide" <zide.chen@...el.com>, Peter Zijlstra
 <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>,
 Adrian Hunter <adrian.hunter@...el.com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Andi Kleen <ak@...ux.intel.com>, Eranian Stephane <eranian@...gle.com>
Cc: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
 Xudong Hao <xudong.hao@...el.com>, Falcon Thomas <thomas.falcon@...el.com>,
 Steve Wahl <steve.wahl@....com>
Subject: Re: [PATCH 1/2] perf/x86/intel/uncore: Skip discovery table for
 offline dies


On 10/30/2025 12:38 PM, Chen, Zide wrote:
> On 10/29/2025 6:37 PM, Mi, Dapeng wrote:
>> On 10/30/2025 6:07 AM, Zide Chen wrote:
>>> This warning can be triggered if NUMA is disabled and the system
>>> boots with fewer CPUs than the number of CPUs in die 0.
>>>
>>> WARNING: CPU: 9 PID: 7257 at uncore.c:1157 uncore_pci_pmu_register+0x136/0x160 [intel_uncore]
>>>
>>> Currently, the discovery table continues to be parsed even if all CPUs
>>> in the associated die are offline. This can lead to an array overflow
>>> at "pmu->boxes[die] = box" in uncore_pci_pmu_register(), which may
>>> trigger the warning above or cause other issues.
>>>
>>> Reported-by: Steve Wahl <steve.wahl@....com>
>>> Fixes: edae1f06c2cd ("perf/x86/intel/uncore: Parse uncore discovery tables")
>>> Signed-off-by: Zide Chen <zide.chen@...el.com>
>>> ---
>>>  arch/x86/events/intel/uncore.c           | 4 ++++
>>>  arch/x86/events/intel/uncore_discovery.c | 2 +-
>>>  2 files changed, 5 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/x86/events/intel/uncore.c b/arch/x86/events/intel/uncore.c
>>> index ee586eb714ec..5c3aeea5c78d 100644
>>> --- a/arch/x86/events/intel/uncore.c
>>> +++ b/arch/x86/events/intel/uncore.c
>>> @@ -1380,6 +1380,10 @@ static void uncore_pci_pmus_register(void)
>>>  
>>>  		for (node = rb_first(type->boxes); node; node = rb_next(node)) {
>>>  			unit = rb_entry(node, struct intel_uncore_discovery_unit, node);
>>> +
>>> +			if (WARN_ON(unit->die >= uncore_max_dies()))
>> Base on my understanding, it seems an valid situation which could happen.
>> If so, we'd better remove the WARN_on to avoid it mislead users. Thanks.
> Now, for invalid or offline die IDs, we skip parsing the discovery
> table, and no PMON units are expected to be inserted into the RB tree.
> Therefore, using WARN_ON() here seems appropriate.
>
> I put a WARN_ON() here because invalid die ID could cause array overflow.

Ok, it's good then. Thanks.


>
>  >> +				continue;
>>> +
>>>  			pdev = pci_get_domain_bus_and_slot(UNCORE_DISCOVERY_PCI_DOMAIN(unit->addr),
>>>  							   UNCORE_DISCOVERY_PCI_BUS(unit->addr),
>>>  							   UNCORE_DISCOVERY_PCI_DEVFN(unit->addr));
>>> diff --git a/arch/x86/events/intel/uncore_discovery.c b/arch/x86/events/intel/uncore_discovery.c
>>> index 1bf6e4288577..d6aee12139f1 100644
>>> --- a/arch/x86/events/intel/uncore_discovery.c
>>> +++ b/arch/x86/events/intel/uncore_discovery.c
>>> @@ -388,7 +388,7 @@ static bool intel_uncore_has_discovery_tables_pci(int *ignore)
>>>  				     (val & UNCORE_DISCOVERY_DVSEC2_BIR_MASK) * UNCORE_DISCOVERY_BIR_STEP;
>>>  
>>>  			die = get_device_die_id(dev);
>>> -			if (die < 0)
>>> +			if ((die < 0) || (die >= uncore_max_dies()))
>>>  				continue;
>>>  
>>>  			parse_discovery_table(dev, die, bar_offset, &parsed, ignore);