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

From: Kuppuswamy Sathyanarayanan <[email-masked]>
Date: Thu, 13 Jun 2024 20:05:32 -0700

On 6/13/24 7:39 PM, Duan, Zhenzhong wrote:
> Hi
>
>> -----Original Message-----
>> From: Kuppuswamy Sathyanarayanan
>> <[email-masked]>
>> 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 <[email-masked]>
>>> Co-developed-by: "Wang, Qingshun" <[email-masked]>
>>> Signed-off-by: "Wang, Qingshun" <[email-masked]>
>>> Signed-off-by: Zhenzhong Duan <[email-masked]>
>>> ---
>>>  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. */
>
> 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

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer