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

["Mi, Dapeng" <dapeng1.mi@linux.intel.com>]

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.


>
>
>> 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 */