AER: PCI Express Advanced Error Reporting
Overview
1. What is the PCI Express AER Driver?
PCI Express error signaling can occur on the PCI Express link itself or on behalf of transactions initiated on the link. PCI Express defines two error reporting paradigms: the baseline capability and the Advanced Error Reporting capability. The baseline capability is required of all PCI Express components providing a minimum defined set of error reporting requirement . Advanced Error Reporting capability is implemented with a PCI Express advanced error reporting extended capability structure providing more robust error reporting.
The PCI Express AER driver provides the infrastructure to support PCI Express Advanced Error Reporting capability. The PCI Express AER driver provides three basic functions:
- Gathers the comprehensive error information if errors occurred.
- Reports error to the users.
- Performs error recovery actions.
AER driver only attaches root ports which support PCI-Express AER capability.
2. How AER does work?
PCI Express errors are classified into two types: correctable errors and uncorrectable errors. This classification is based on the impacts of those errors, which may result in degraded performance or function failure.
- Correctable errors pose no impacts on the functionality of the interface. The PCI Express protocol can recover without any software intervention or any loss of data. These errors are detected and corrected by hardware. The AER driver clears the device's correctable error status register accordingly and logs these errors.
- Unlike correctable errors, uncorrectable errors impact functionality of the interface. Uncorrectable errors can cause a particular transaction or a particular PCI Express link to be unreliable.
- Depending on those error conditions, uncorrectable errors are further classified into non-fatal errors and fatal errors.
- Non-fatal errors cause the particular transaction to be unreliable, but the PCI Express link itself is fully functional.
- Fatal errors, on the other hand, cause the link to be unreliable.
When AER is enabled, a PCI Express device will automatically send an error message to the PCIe root port above it when the device captures an error. The Root Port, upon receiving an error reporting message, internally processes and logs the error message in its PCI Express capability structure. Error information being logged includes storing the error reporting agent's requestor ID into the Error Source Identification Registers and setting the error bits of the Root Error Status Register accordingly. If AER error reporting is enabled in Root Error Command Register, the Root Port generates an interrupt if an error is detected.
Note that the errors as described above are related to the PCI Express hierarchy and links. These errors do not include any device specific errors because device specific errors will still get sent directly to the device driver.
User Guide
1. Include the PCI Express AER Root Driver into the Linux Kernel
The PCI Express AER Root driver is a Root Port service driver attached to the PCI Express Port Bus driver. If a user wants to use it, the driver has to be compiled. Option CONFIG_PCIEAER supports this capability. It depends on CONFIG_PCIEPORTBUS, so pls. set CONFIG_PCIEPORTBUS=y and CONFIG_PCIEAER=y.
2. Load PCI Express AER Root Driver
Some systems have AER support in firmware. Enabling Linux AER support at the same time the firmware handles AER may result in unpredictable behavior. Therefore, Linux does not handle AER events unless the firmware grants AER control to the OS via the ACPI _OSC method. See the PCI FW 3.0 Specification for details regarding _OSC usage.
3. AER error output
When a PCIe AER error is captured, an error message will be output to console. If it's a correctable error, it is output as a warning. Otherwise, it is printed as an error. So users could choose different log level to filter out correctable error messages.
Below shows an example:
代码语言：javascript复制0000:50:00.0: PCIe Bus Error: severity=Uncorrected (Fatal), type=Transaction Layer, id=0500(Requester ID)
0000:50:00.0: device [8086:0329] error status/mask=00100000/00000000
0000:50:00.0: [20] Unsupported Request (First)
0000:50:00.0: TLP Header: 04000001 00200a03 05010000 00050100In the example, RequesterID means the ID of the device who sends the error message to root port. Pls. refer to pci express specs for other fields.
4. AER Statistics / Counters
When PCIe AER errors are captured, the counters / statistics are also exposed in the form of sysfs attributes which are documented at Documentation/ABI/testing/sysfs-bus-pci-devices-aer_stats
Documentation/ABI/testing/sysfs-bus-pci-devices-aer_stats
代码语言：javascript复制==========================
PCIe Device AER statistics
==========================
These attributes show up under all the devices that are AER capable. These
statistical counters indicate the errors "as seen/reported by the device".
Note that this may mean that if an endpoint is causing problems, the AER
counters may increment at its link partner (e.g. root port) because the
errors may be "seen" / reported by the link partner and not the
problematic endpoint itself (which may report all counters as 0 as it never
saw any problems).
What: /sys/bus/pci/devices/<dev>/aer_dev_correctable
Date: July 2018
KernelVersion: 4.19.0
Contact: linux-pci@vger.kernel.org, rajatja@google.com
Description: List of correctable errors seen and reported by this
PCI device using ERR_COR. Note that since multiple errors may
be reported using a single ERR_COR message, thus
TOTAL_ERR_COR at the end of the file may not match the actual
total of all the errors in the file. Sample output:
-------------------------------------------------------------------------
localhost /sys/devices/pci0000:00/0000:00:1c.0 # cat aer_dev_correctable
Receiver Error 2
Bad TLP 0
Bad DLLP 0
RELAY_NUM Rollover 0
Replay Timer Timeout 0
Advisory Non-Fatal 0
Corrected Internal Error 0
Header Log Overflow 0
TOTAL_ERR_COR 2
-------------------------------------------------------------------------
What: /sys/bus/pci/devices/<dev>/aer_dev_fatal
Date: July 2018
KernelVersion: 4.19.0
Contact: linux-pci@vger.kernel.org, rajatja@google.com
Description: List of uncorrectable fatal errors seen and reported by this
PCI device using ERR_FATAL. Note that since multiple errors may
be reported using a single ERR_FATAL message, thus
TOTAL_ERR_FATAL at the end of the file may not match the actual
total of all the errors in the file. Sample output:
-------------------------------------------------------------------------
localhost /sys/devices/pci0000:00/0000:00:1c.0 # cat aer_dev_fatal
Undefined 0
Data Link Protocol 0
Surprise Down Error 0
Poisoned TLP 0
Flow Control Protocol 0
Completion Timeout 0
Completer Abort 0
Unexpected Completion 0
Receiver Overflow 0
Malformed TLP 0
ECRC 0
Unsupported Request 0
ACS Violation 0
Uncorrectable Internal Error 0
MC Blocked TLP 0
AtomicOp Egress Blocked 0
TLP Prefix Blocked Error 0
TOTAL_ERR_FATAL 0
-------------------------------------------------------------------------
What: /sys/bus/pci/devices/<dev>/aer_dev_nonfatal
Date: July 2018
KernelVersion: 4.19.0
Contact: linux-pci@vger.kernel.org, rajatja@google.com
Description: List of uncorrectable nonfatal errors seen and reported by this
PCI device using ERR_NONFATAL. Note that since multiple errors
may be reported using a single ERR_FATAL message, thus
TOTAL_ERR_NONFATAL at the end of the file may not match the
actual total of all the errors in the file. Sample output:
-------------------------------------------------------------------------
localhost /sys/devices/pci0000:00/0000:00:1c.0 # cat aer_dev_nonfatal
Undefined 0
Data Link Protocol 0
Surprise Down Error 0
Poisoned TLP 0
Flow Control Protocol 0
Completion Timeout 0
Completer Abort 0
Unexpected Completion 0
Receiver Overflow 0
Malformed TLP 0
ECRC 0
Unsupported Request 0
ACS Violation 0
Uncorrectable Internal Error 0
MC Blocked TLP 0
AtomicOp Egress Blocked 0
TLP Prefix Blocked Error 0
TOTAL_ERR_NONFATAL 0
-------------------------------------------------------------------------
============================
PCIe Rootport AER statistics
============================
These attributes show up under only the rootports (or root complex event
collectors) that are AER capable. These indicate the number of error messages as
"reported to" the rootport. Please note that the rootports also transmit
(internally) the ERR_* messages for errors seen by the internal rootport PCI
device, so these counters include them and are thus cumulative of all the error
messages on the PCI hierarchy originating at that root port.
What: /sys/bus/pci/devices/<dev>/aer_stats/aer_rootport_total_err_cor
Date: July 2018
KernelVersion: 4.19.0
Contact: linux-pci@vger.kernel.org, rajatja@google.com
Description: Total number of ERR_COR messages reported to rootport.
What: /sys/bus/pci/devices/<dev>/aer_stats/aer_rootport_total_err_fatal
Date: July 2018
KernelVersion: 4.19.0
Contact: linux-pci@vger.kernel.org, rajatja@google.com
Description: Total number of ERR_FATAL messages reported to rootport.
What: /sys/bus/pci/devices/<dev>/aer_stats/aer_rootport_total_err_nonfatal
Date: July 2018
KernelVersion: 4.19.0
Contact: linux-pci@vger.kernel.org, rajatja@google.com
Description: Total number of ERR_NONFATAL messages reported to rootport.
