RE: [PATCH v4 1/3] PCI/AER: Store UNCOR_STATUS bits that might be ANFE in aer_err_info

Duan, Zhenzhong
2024-06-14T03:14:06Z

>-----Original Message-----
>From: Kuppuswamy Sathyanarayanan
><sathyanarayanan.kuppuswamy@linux.intel.com>
>Subject: Re: [PATCH v4 1/3] PCI/AER: Store UNCOR_STATUS bits that might
>be ANFE in aer_err_info
>
>
>On 6/13/24 7:39 PM, Duan, Zhenzhong wrote:
>> Hi
>>
>>> -----Original Message-----
>>> From: Kuppuswamy Sathyanarayanan
>>> <sathyanarayanan.kuppuswamy@linux.intel.com>
>>> Subject: Re: [PATCH v4 1/3] PCI/AER: Store UNCOR_STATUS bits that
>might
>>> be ANFE in aer_err_info
>>>
>>> Hi,
>>>
>>> On 5/9/24 1:48 AM, Zhenzhong Duan wrote:
>>>> In some cases the detector of a Non-Fatal Error(NFE) is not the most
>>>> appropriate agent to determine the type of the error. For example,
>>>> when software performs a configuration read from a non-existent
>>>> device or Function, completer will send an ERR_NONFATAL Message.
>>>> On some platforms, ERR_NONFATAL results in a System Error, which
>>>> breaks normal software probing.
>>>>
>>>> Advisory Non-Fatal Error(ANFE) is a special case that can be used
>>>> in above scenario. It is predominantly determined by the role of the
>>>> detecting agent (Requester, Completer, or Receiver) and the specific
>>>> error. In such cases, an agent with AER signals the NFE (if enabled)
>>>> by sending an ERR_COR Message as an advisory to software, instead of
>>>> sending ERR_NONFATAL.
>>>>
>>>> When processing an ANFE, ideally both correctable error(CE) status and
>>>> uncorrectable error(UE) status should be cleared. However, there is no
>>>> way to fully identify the UE associated with ANFE. Even worse, Non-Fatal
>>>> Error(NFE) may set the same UE status bit as ANFE. Treating an ANFE as
>>>> NFE will reproduce above mentioned issue, i.e., breaking softwore
>probing;
>>>> treating NFE as ANFE will make us ignoring some UEs which need active
>>>> recover operation. To avoid clearing UEs that are not ANFE by accident,
>>>> the most conservative route is taken here: If any of the NFE Detected
>>>> bits is set in Device Status, do not touch UE status, they should be
>>>> cleared later by the UE handler. Otherwise, a specific set of UEs that
>>>> may be raised as ANFE according to the PCIe specification will be cleared
>>>> if their corresponding severity is Non-Fatal.
>>>>
>>>> To achieve above purpose, store UNCOR_STATUS bits that might be
>ANFE
>>>> in aer_err_info.anfe_status. So that those bits could be printed and
>>>> processed later.
>>>>
>>>> Tested-by: Yudong Wang <yudong.wang@intel.com>
>>>> Co-developed-by: "Wang, Qingshun" <qingshun.wang@linux.intel.com>
>>>> Signed-off-by: "Wang, Qingshun" <qingshun.wang@linux.intel.com>
>>>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
>>>> ---
>>>> drivers/pci/pci.h | 1 +
>>>> drivers/pci/pcie/aer.c | 53
>>> ++++++++++++++++++++++++++++++++++++++++++
>>>> 2 files changed, 54 insertions(+)
>>>>
>>>> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
>>>> index 17fed1846847..3f9eb807f9fd 100644
>>>> --- a/drivers/pci/pci.h
>>>> +++ b/drivers/pci/pci.h
>>>> @@ -412,6 +412,7 @@ struct aer_err_info {
>>>>
>>>> unsigned int status; /* COR/UNCOR Error Status */
>>>> unsigned int mask; /* COR/UNCOR Error Mask */
>>>> + unsigned int anfe_status; /* UNCOR Error Status for ANFE */
>>>> struct pcie_tlp_log tlp; /* TLP Header */
>>>> };
>>>>
>>>> diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
>>>> index ac6293c24976..f2839b51321a 100644
>>>> --- a/drivers/pci/pcie/aer.c
>>>> +++ b/drivers/pci/pcie/aer.c
>>>> @@ -107,6 +107,12 @@ struct aer_stats {
>>>> PCI_ERR_ROOT_MULTI_COR_RCV |
>>> \
>>>> PCI_ERR_ROOT_MULTI_UNCOR_RCV)
>>>>
>>>> +#define AER_ERR_ANFE_UNC_MASK
>>> (PCI_ERR_UNC_POISON_TLP | \
>>>> + PCI_ERR_UNC_COMP_TIME |
>>> \
>>>> + PCI_ERR_UNC_COMP_ABORT |
>>> \
>>>> + PCI_ERR_UNC_UNX_COMP |
>>> \
>>>> + PCI_ERR_UNC_UNSUP)
>>>> +
>>>> static int pcie_aer_disable;
>>>> static pci_ers_result_t aer_root_reset(struct pci_dev *dev);
>>>>
>>>> @@ -1196,6 +1202,49 @@ void aer_recover_queue(int domain,
>unsigned
>>> int bus, unsigned int devfn,
>>>> EXPORT_SYMBOL_GPL(aer_recover_queue);
>>>> #endif
>>>>
>>>> +static void anfe_get_uc_status(struct pci_dev *dev, struct aer_err_info
>>> *info)
>>>> +{
>>>> + u32 uncor_mask, uncor_status, anfe_status;
>>>> + u16 device_status;
>>>> + int aer = dev->aer_cap;
>>>> +
>>>> + pci_read_config_dword(dev, aer + PCI_ERR_UNCOR_STATUS,
>>> &uncor_status);
>>>> + pci_read_config_dword(dev, aer + PCI_ERR_UNCOR_MASK,
>>> &uncor_mask);
>>>> + /*
>>>> + * According to PCIe Base Specification Revision 6.1,
>>>> + * Section 6.2.3.2.4, if an UNCOR error is raised as
>>>> + * Advisory Non-Fatal error, it will match the following
>>>> + * conditions:
>>>> + * a. The severity of the error is Non-Fatal.
>>>> + * b. The error is one of the following:
>>>> + * 1. Poisoned TLP (Section 6.2.3.2.4.3)
>>>> + * 2. Completion Timeout (Section 6.2.3.2.4.4)
>>>> + * 3. Completer Abort (Section 6.2.3.2.4.1)
>>>> + * 4. Unexpected Completion (Section 6.2.3.2.4.5)
>>>> + * 5. Unsupported Request (Section 6.2.3.2.4.1)
>>>> + */
>>>> + anfe_status = uncor_status & ~uncor_mask & ~info->severity &
>>>> + AER_ERR_ANFE_UNC_MASK;
>>>> +
>>>> + if (pcie_capability_read_word(dev, PCI_EXP_DEVSTA,
>>> &device_status))
>>>> + return;
>>>> + /*
>>>> + * Take the most conservative route here. If there are Non-Fatal
>>> errors
>>>> + * detected, do not assume any bit in uncor_status is set by ANFE.
>>>> + */
>>>> + if (device_status & PCI_EXP_DEVSTA_NFED)
>>>> + return;
>>> You can move this check to the top of the function. You don't need to
>check
>>> the rest if NFE error is detected in device status.
>> The v3 just worked that way. Jonathan pointed a race that NFE triggered
>after
>> the check will be treated as ANFE and cleared. Check it after reading
>UNCOR_STATUS
>> can avoid the race.
>>
>> See https://lkml.org/lkml/2024/4/22/1011 for discussion details.
>
>Got it. I would recommend adding a comment about it in handler. May be
>some thing like,
>
>/*
> * To avoid race between device status read and error status register read,
>cache
> * uncorrectable error status before checking for NFE in device status *
>register. */

Good suggestion, will add.

Thanks
Zhenzhong