Re: [PATCH V6 4/5] perf/x86/intel/uncore: Fix PMON enumeration with NUMA disabled

["Chen, Zide" <zide.chen@intel.com>]

On 4/1/2026 7:48 PM, Mi, Dapeng wrote:
> 
> On 4/2/2026 4:25 AM, Chen, Zide wrote:
>>
>> On 3/30/2026 6:26 PM, Mi, Dapeng wrote:
>>> On 3/31/2026 5:24 AM, Zide Chen wrote:
>>>> When NUMA is disabled on a NUMA-capable platform, UPI and M3UPI PMON
>>>> units are not enumerated.
>>>>
>>>> In this case, pcibus_to_node() always returns NUMA_NO_NODE, causing
>>>> uncore_device_to_die() to return -1 for all PCI devices. As a result,
>>>> the corresponding PMON units are not added to the RB tree.
>>>>
>>>> These PMON units are per-die resources, and their utility when NUMA is
>>>> disabled is limited.  The driver does not prohibit their use, and the
>>>> enumeration should still work correctly.
>>>>
>>>> Fix this by using uncore_pcibus_to_dieid(), which works regardless of
>>>> whether NUMA is enabled.  This requires calling
>>>> snbep_pci2phy_map_init() in spr_uncore_pci_init().
>>>>
>>>> Since pci_init() is called before mmio_init(), remove the redundant
>>>> snbep_pci2phy_map_init() call from spr_uncore_mmio_init().  If
>>>> snbep_pci2phy_map_init() fails, uncore driver should be bailed out,
>>>> so the fallback path in spr_uncore_mmio_init() can be removed.
>>>>
>>>> Signed-off-by: Zide Chen <zide.chen@intel.com>
>>>> ---
>>>> V6:
>>>> - Split from patch v5 3/4.
>>>> - Remove the redundant call in spr_uncore_mmio_init().
>>>> - Update commit messages.
>>>> ---
>>>>  arch/x86/events/intel/uncore.c       |  1 +
>>>>  arch/x86/events/intel/uncore_snbep.c | 26 +++++++++++---------------
>>>>  2 files changed, 12 insertions(+), 15 deletions(-)
>>>>
>>>> diff --git a/arch/x86/events/intel/uncore.c b/arch/x86/events/intel/uncore.c
>>>> index 786bd51a0d89..e9cc1ba921c5 100644
>>>> --- a/arch/x86/events/intel/uncore.c
>>>> +++ b/arch/x86/events/intel/uncore.c
>>>> @@ -67,6 +67,7 @@ int uncore_die_to_segment(int die)
>>>>  	return bus ? pci_domain_nr(bus) : -EINVAL;
>>>>  }
>>>>  
>>>> +/* Note: This API can only be used when NUMA information is available. */
>>>>  int uncore_device_to_die(struct pci_dev *dev)
>>>>  {
>>>>  	int node = pcibus_to_node(dev->bus);
>>>> diff --git a/arch/x86/events/intel/uncore_snbep.c b/arch/x86/events/intel/uncore_snbep.c
>>>> index 8ee06d4659bb..73da1e88e286 100644
>>>> --- a/arch/x86/events/intel/uncore_snbep.c
>>>> +++ b/arch/x86/events/intel/uncore_snbep.c
>>>> @@ -6415,7 +6415,7 @@ static void spr_update_device_location(int type_id)
>>>>  
>>>>  	while ((dev = pci_get_device(PCI_VENDOR_ID_INTEL, device, dev)) != NULL) {
>>>>  
>>>> -		die = uncore_device_to_die(dev);
>>>> +		die = uncore_pcibus_to_dieid(dev->bus);
>>>>  		if (die < 0)
>>>>  			continue;
>>>>  
>>>> @@ -6439,6 +6439,10 @@ static void spr_update_device_location(int type_id)
>>>>  
>>>>  int spr_uncore_pci_init(void)
>>>>  {
>>>> +	int ret = snbep_pci2phy_map_init(0x3250, SKX_CPUNODEID, SKX_GIDNIDMAP, true);
>>>> +	if (ret)
>>>> +		return ret;
>>>> +
>>>>  	/*
>>>>  	 * The discovery table of UPI on some SPR variant is broken,
>>>>  	 * which impacts the detection of both UPI and M3UPI uncore PMON.
>>>> @@ -6460,21 +6464,13 @@ int spr_uncore_pci_init(void)
>>>>  
>>>>  void spr_uncore_mmio_init(void)
>>>>  {
>>>> -	int ret = snbep_pci2phy_map_init(0x3250, SKX_CPUNODEID, SKX_GIDNIDMAP, true);
>>>> +	uncore_mmio_uncores = uncore_get_uncores(UNCORE_ACCESS_MMIO,
>>>> +						 UNCORE_SPR_MMIO_EXTRA_UNCORES,
>>>> +						 spr_mmio_uncores,
>>>> +						 UNCORE_SPR_NUM_UNCORE_TYPES,
>>>> +						 spr_uncores);
>>>>  
>>>> -	if (ret) {
>>>> -		uncore_mmio_uncores = uncore_get_uncores(UNCORE_ACCESS_MMIO, 0, NULL,
>>>> -							 UNCORE_SPR_NUM_UNCORE_TYPES,
>>>> -							 spr_uncores);
>>>> -	} else {
>>>> -		uncore_mmio_uncores = uncore_get_uncores(UNCORE_ACCESS_MMIO,
>>>> -							 UNCORE_SPR_MMIO_EXTRA_UNCORES,
>>>> -							 spr_mmio_uncores,
>>>> -							 UNCORE_SPR_NUM_UNCORE_TYPES,
>>>> -							 spr_uncores);
>>>> -
>>>> -		spr_uncore_imc_free_running.num_boxes = uncore_type_max_boxes(uncore_mmio_uncores, UNCORE_SPR_IMC) / 2;
>>>> -	}
>>>> +	spr_uncore_imc_free_running.num_boxes = uncore_type_max_boxes(uncore_mmio_uncores, UNCORE_SPR_IMC) / 2;
>>> I'm not sure if we can directly remove the snbep_pci2phy_map_init() call
>>> here. In theory, the snbep_pci2phy_map_init() call in spr_uncore_pci_init()
>>> could fail and then spr_uncore_mmio_init() doesn't know it and directly
>>> initializes MMIO PMU, then it could lead to the MMIO initialization fails.
>>
>> Yes, this is true. But I would argue that the fix in this patch is
>> correct, and the issue you pointed out is not new: the uncore driver
>> registers a PMU device without guaranteeing it's functioning.
>>
>> This is because the Intel uncore driver employs a lazy init approach.
>> And when init_box() fails, it doesn't unregister the inaccessible PMU
>> devices. For example, intel_generic_uncore_mmio_init_box() could fail
>> for a number of reasons, making all associated PMU devices non-functional.
>>
>> Originally the uncore driver tried to enumerate PCI/MSR/MMIO uncore
>> independently, but evolving hardware complexity makes this more
>> challenging.  This patch is just one example, IMC Freerunning is
>> MMIO-accessed but relies on PCI devices to read the die-specific MMIO
>> base address. Explicitly gating sysfs node creation with PCI init code
>> in mmio_init() is neither clean nor reliable.
>>
>> To fix it, it seems reasonable to have init_box() return int and
>> unregister the PMU device if deemed inaccessible — similar to what
>> perf_event_ibs_init() does.
>>
>> --- a/arch/x86/events/intel/uncore.h
>> +++ b/arch/x86/events/intel/uncore.h
>> @@ -129,7 +129,7 @@ struct intel_uncore_type {
>>  #define events_group attr_groups[2]
>>
>>  struct intel_uncore_ops {
>> -       void (*init_box)(struct intel_uncore_box *);
>> +       int (*init_box)(struct intel_uncore_box *);
>>
>> --- a/arch/x86/events/intel/uncore.c
>> +++ b/arch/x86/events/intel/uncore.c
>> @@ -1155,7 +1155,8 @@ static int uncore_pci_pmu_register(struct pci_dev
>> *pdev,
>>         box->dieid = die;
>>         box->pci_dev = pdev;
>>         box->pmu = pmu;
>> -       uncore_box_init(box);
>> +       ret = uncore_box_init(box);
>> +	if (ret)
>> +               return ret;
>>
>> @@ -1598,8 +1599,10 @@ static int uncore_box_ref(struct
>> intel_uncore_type **types,
>>                 pmu = type->pmus;
>>                 for (i = 0; i < type->num_boxes; i++, pmu++) {
>>                         box = pmu->boxes[id];
>> -                       if (box && box->cpu >= 0 &&
>> atomic_inc_return(&box->refcnt) == 1)
>> -                               uncore_box_init(box);
>> +                       if (box && box->cpu >= 0 &&
>> atomic_inc_return(&box->refcnt) == 1)
>> +                               if (uncore_box_init(box))
>> +                                       uncore_pmu_unregister(pmu);
> 
> Yes, I like this idea. The return value of init_box() should always be
> checked. I'm not quite sure if there are other resources need to be cleaned
> besides unregistering the corresponding uncore pmu, please double check.
> Thanks.

I'm thinking of removing this patch from this series and putting it
together with the init_box() changes, where it will be a complete fix
and I need more time to double check all the init_box() callbacks.

>>
>>
>>> Currently the PCI, CPU and MMIO initialization are totally independent,
>>> only when the 3 types initialization all fail, then uncore PMU can abort.
>>>
>>> ``` 
>>>
>>>    if (uncore_init->pci_init) {
>>>         pret = uncore_init->pci_init();
>>>         if (!pret)
>>>             pret = uncore_pci_init();
>>>     }
>>>
>>>     if (uncore_init->cpu_init) {
>>>         uncore_init->cpu_init();
>>>         cret = uncore_cpu_init();
>>>     }
>>>
>>>     if (uncore_init->mmio_init) {
>>>         uncore_init->mmio_init();
>>>         mret = uncore_mmio_init();
>>>     }
>>>
>>>     if (cret && pret && mret) {
>>>         ret = -ENODEV;
>>>         goto free_discovery;
>>>     }
>>> ```
>>>
>>>
>>>>  }
>>>>  
>>>>  /* end of SPR uncore support */