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

Duan, Zhenzhong
2024-06-14T02:39:49Z

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.

Thanks
Zhenzhong

>
>> +
>> + /*
>> + * If there is another ANFE between reading uncor_status and
>clearing
>> + * PCI_ERR_COR_ADV_NFAT bit in cor_status register, that ANFE
>isn't
>> + * recorded in info->anfe_status. It will be read out as NFE in
>> + * following uncor_status register reading and processed by NFE
>> + * handler.
>> + */
>> + info->anfe_status = anfe_status;
>> +}
>> +
>> /**
>> * aer_get_device_error_info - read error status from dev and store it to
>info
>> * @dev: pointer to the device expected to have a error record
>> @@ -1213,6 +1262,7 @@ int aer_get_device_error_info(struct pci_dev
>*dev, struct aer_err_info *info)
>>
>> /* Must reset in this function */
>> info->status = 0;
>> + info->anfe_status = 0;
>> info->tlp_header_valid = 0;
>>
>> /* The device might not support AER */
>> @@ -1226,6 +1276,9 @@ int aer_get_device_error_info(struct pci_dev
>*dev, struct aer_err_info *info)
>> &info->mask);
>> if (!(info->status & ~info->mask))
>> return 0;
>> +
>> + if (info->status & PCI_ERR_COR_ADV_NFAT)
>> + anfe_get_uc_status(dev, info);
>> } else if (type == PCI_EXP_TYPE_ROOT_PORT ||
>> type == PCI_EXP_TYPE_RC_EC ||
>> type == PCI_EXP_TYPE_DOWNSTREAM ||
>
>--
>Sathyanarayanan Kuppuswamy
>Linux Kernel Developer