Re: [PATCH v11 18/23] PCI/AER: Dequeue forwarded CXL error

["Bowman, Terry" <terry.bowman@amd.com>]

On 8/28/2025 7:43 PM, Dave Jiang wrote:
>
> On 8/26/25 6:35 PM, Terry Bowman wrote:
>> The AER driver is now designed to forward CXL protocol errors to the CXL
> I would rephrase it to:
> The AER driver enqueues the CXL protocol error info to the created kfifo for the CXL driver to consume.
>  
>> driver. Update the CXL driver with functionality to dequeue the forwarded
>> CXL error from the kfifo. Also, update the CXL driver to begin the protocol
>> error handling processing using the work received from the FIFO.
>>
>> Update function cxl_proto_err_work_fn() to dequeue work forwarded by the
>> AER service driver. This will begin the CXL protocol error processing with
>> a call to cxl_handle_proto_error().
>>
>> Introduce logic to take the SBDF values from 'struct cxl_proto_error_info'
>> and use in discovering the erring PCI device. The call to pci_get_domain_bus_and_slot()
>> will return a reference counted 'struct pci_dev *'. This will serve as
>> reference count to prevent releasing the CXL Endpoint's mapped RAS while
>> handling the error. Use scope base __free() to put the reference count.
>> This will change when adding support for CXL port devices in the future.
>>
>> Implement cxl_handle_proto_error() to differentiate between Restricted CXL
>> Host (RCH) protocol errors and CXL virtual host (VH) protocol errors.
>> Maintain the existing RCH handling. Export the AER driver's pcie_walk_rcec()
>> allowing the CXL driver to walk the RCEC's secondary bus.
>>
>> VH correctable error (CE) processing will call the CXL CE handler. VH
>> uncorrectable errors (UCE) will call cxl_do_recovery(), implemented as a
>> stub for now and to be updated in future patch. Export pci_aer_clean_fatal_status()
>> and pci_clean_device_status() used to clean up AER status after handling.
>>
>> Signed-off-by: Terry Bowman <terry.bowman@amd.com>
>> Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
>>
>> ---
>> Changes in v10->v11:
>> - Reword patch commit message to remove RCiEP details (Jonathan)
>> - Add #include <linux/bitfield.h> (Terry)
>> - is_cxl_rcd() - Fix short comment message wrap  (Jonathan)
>> - is_cxl_rcd() - Combine return calls into 1  (Jonathan)
>> - cxl_handle_proto_error() - Move comment earlier  (Jonathan)
>> - Usse FIELD_GET() in discovering class code (Jonathan)
>> - Remove BDF from cxl_proto_err_work_data. Use 'struct pci_dev *' (Dan)
>> ---
>>  drivers/cxl/core/ras.c  | 68 ++++++++++++++++++++++++++++++++++-------
>>  drivers/pci/pci.c       |  1 +
>>  drivers/pci/pci.h       |  7 -----
>>  drivers/pci/pcie/aer.c  |  1 +
>>  drivers/pci/pcie/rcec.c |  1 +
>>  include/linux/aer.h     |  2 ++
>>  include/linux/pci.h     | 10 ++++++
>>  7 files changed, 72 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/cxl/core/ras.c b/drivers/cxl/core/ras.c
>> index b285448c2d9c..a2e95c49f965 100644
>> --- a/drivers/cxl/core/ras.c
>> +++ b/drivers/cxl/core/ras.c
>> @@ -118,17 +118,6 @@ static void cxl_cper_prot_err_work_fn(struct work_struct *work)
>>  }
>>  static DECLARE_WORK(cxl_cper_prot_err_work, cxl_cper_prot_err_work_fn);
>>  
>> -int cxl_ras_init(void)
>> -{
>> -	return cxl_cper_register_prot_err_work(&cxl_cper_prot_err_work);
>> -}
>> -
>> -void cxl_ras_exit(void)
>> -{
>> -	cxl_cper_unregister_prot_err_work(&cxl_cper_prot_err_work);
>> -	cancel_work_sync(&cxl_cper_prot_err_work);
>> -}
>> -
>>  static pci_ers_result_t cxl_handle_ras(struct device *dev, u64 serial, void __iomem *ras_base);
>>  static void cxl_handle_cor_ras(struct device *dev, u64 serial, void __iomem *ras_base);
>>  
>> @@ -331,6 +320,10 @@ void cxl_endpoint_port_init_ras(struct cxl_port *ep)
>>  }
>>  EXPORT_SYMBOL_NS_GPL(cxl_endpoint_port_init_ras, "CXL");
>>  
>> +static void cxl_do_recovery(struct device *dev)
>> +{
>> +}
>> +
>>  static void cxl_handle_cor_ras(struct device *dev, u64 serial, void __iomem *ras_base)
>>  {
>>  	void __iomem *addr;
>> @@ -472,3 +465,56 @@ pci_ers_result_t pci_error_detected(struct pci_dev *pdev,
>>  	return rc;
>>  }
>>  EXPORT_SYMBOL_NS_GPL(pci_error_detected, "CXL");
>> +
>> +static void cxl_handle_proto_error(struct cxl_proto_err_work_data *err_info)
>> +{
>> +	struct pci_dev *pdev = err_info->pdev;
>> +	struct cxl_dev_state *cxlds = pci_get_drvdata(pdev);
> So this function is called from the workqueue thread to consume data from the kfifo right? Do we need to take the device lock of the pdev to ensure that a driver is bound to the device before we attempt to retrieve the data? And do we also need to verify that the driver bound is the cxl_pci driver (and not something like vfio_pci)? Otherwise I think assuming the drv data is cxl_dev_state may cause crash.
>
> DJ

Yes, this is called in the worker thread context. I added the pdev device locks
later in cxl_report_error_detected() for the UCE case. I found it necessary to 
put in this function and not in cxl_handle_proto_error() (here) because of the 
traversing logic in the UCE handling flow where it needs to be locked but only
exactly once. I didn't add for the CE because I wasn't certain a CE error was 
enough reason to add a device lock. 

The UCE flow is:

cxl_handle_proto_error()
--> cxl_do_recovery()
----> cxl_handle_proto_error() <--- Added device lock here because of topo traversing/iteration


I tried adding a function checking for cxl_pci driver but ran into circular dependency 
because the driver is defined in cxl_pci but called from cxl_core. I will revisit
this again but need some ideas how to make that work as I expect it will require 
some code moving. 

Terry

>> +	struct cxl_memdev *cxlmd = cxlds->cxlmd;
>> +	struct device *host_dev __free(put_device) = get_device(&cxlmd->dev);
>> +> +	if (err_info->severity == AER_CORRECTABLE) {
>> +		int aer = pdev->aer_cap;
>> +
>> +		if (aer)
>> +			pci_clear_and_set_config_dword(pdev,
>> +						       aer + PCI_ERR_COR_STATUS,
>> +						       0, PCI_ERR_COR_INTERNAL);
>> +
>> +		cxl_cor_error_detected(&cxlmd->dev);
>> +
>> +		pcie_clear_device_status(pdev);
>> +	} else {
>> +		cxl_do_recovery(&cxlmd->dev);
>> +	}
>> +}
>> +
>> +static void cxl_proto_err_work_fn(struct work_struct *work)
>> +{
>> +	struct cxl_proto_err_work_data wd;
>> +
>> +	while (cxl_proto_err_kfifo_get(&wd))
>> +		cxl_handle_proto_error(&wd);
>> +}
>> +
>> +static struct work_struct cxl_proto_err_work;
>> +static DECLARE_WORK(cxl_proto_err_work, cxl_proto_err_work_fn);
>> +
>> +int cxl_ras_init(void)
>> +{
>> +	if (cxl_cper_register_prot_err_work(&cxl_cper_prot_err_work))
>> +		pr_err("Failed to initialize CXL RAS CPER\n");
>> +
>> +	cxl_register_proto_err_work(&cxl_proto_err_work);
>> +
>> +	return 0;
>> +}
>> +
>> +void cxl_ras_exit(void)
>> +{
>> +	cxl_cper_unregister_prot_err_work(&cxl_cper_prot_err_work);
>> +	cancel_work_sync(&cxl_cper_prot_err_work);
>> +
>> +	cxl_unregister_proto_err_work();
>> +	cancel_work_sync(&cxl_proto_err_work);
>> +}
>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>> index d775ed37a79b..2c9827690cb3 100644
>> --- a/drivers/pci/pci.c
>> +++ b/drivers/pci/pci.c
>> @@ -2328,6 +2328,7 @@ void pcie_clear_device_status(struct pci_dev *dev)
>>  	pcie_capability_read_word(dev, PCI_EXP_DEVSTA, &sta);
>>  	pcie_capability_write_word(dev, PCI_EXP_DEVSTA, sta);
>>  }
>> +EXPORT_SYMBOL_NS_GPL(pcie_clear_device_status, "CXL");
>>  #endif
>>  
>>  /**
>> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
>> index cfa75903dd3f..69ff7c2d214f 100644
>> --- a/drivers/pci/pci.h
>> +++ b/drivers/pci/pci.h
>> @@ -671,16 +671,10 @@ static inline bool pci_dpc_recovered(struct pci_dev *pdev) { return false; }
>>  void pci_rcec_init(struct pci_dev *dev);
>>  void pci_rcec_exit(struct pci_dev *dev);
>>  void pcie_link_rcec(struct pci_dev *rcec);
>> -void pcie_walk_rcec(struct pci_dev *rcec,
>> -		    int (*cb)(struct pci_dev *, void *),
>> -		    void *userdata);
>>  #else
>>  static inline void pci_rcec_init(struct pci_dev *dev) { }
>>  static inline void pci_rcec_exit(struct pci_dev *dev) { }
>>  static inline void pcie_link_rcec(struct pci_dev *rcec) { }
>> -static inline void pcie_walk_rcec(struct pci_dev *rcec,
>> -				  int (*cb)(struct pci_dev *, void *),
>> -				  void *userdata) { }
>>  #endif
>>  
>>  #ifdef CONFIG_PCI_ATS
>> @@ -1022,7 +1016,6 @@ void pci_restore_aer_state(struct pci_dev *dev);
>>  static inline void pci_no_aer(void) { }
>>  static inline void pci_aer_init(struct pci_dev *d) { }
>>  static inline void pci_aer_exit(struct pci_dev *d) { }
>> -static inline void pci_aer_clear_fatal_status(struct pci_dev *dev) { }
>>  static inline int pci_aer_clear_status(struct pci_dev *dev) { return -EINVAL; }
>>  static inline int pci_aer_raw_clear_status(struct pci_dev *dev) { return -EINVAL; }
>>  static inline void pci_save_aer_state(struct pci_dev *dev) { }
>> diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
>> index 627d89ccea9c..45abe1622316 100644
>> --- a/drivers/pci/pcie/aer.c
>> +++ b/drivers/pci/pcie/aer.c
>> @@ -288,6 +288,7 @@ void pci_aer_clear_fatal_status(struct pci_dev *dev)
>>  	if (status)
>>  		pci_write_config_dword(dev, aer + PCI_ERR_UNCOR_STATUS, status);
>>  }
>> +EXPORT_SYMBOL_GPL(pci_aer_clear_fatal_status);
>>  
>>  /**
>>   * pci_aer_raw_clear_status - Clear AER error registers.
>> diff --git a/drivers/pci/pcie/rcec.c b/drivers/pci/pcie/rcec.c
>> index d0bcd141ac9c..fb6cf6449a1d 100644
>> --- a/drivers/pci/pcie/rcec.c
>> +++ b/drivers/pci/pcie/rcec.c
>> @@ -145,6 +145,7 @@ void pcie_walk_rcec(struct pci_dev *rcec, int (*cb)(struct pci_dev *, void *),
>>  
>>  	walk_rcec(walk_rcec_helper, &rcec_data);
>>  }
>> +EXPORT_SYMBOL_NS_GPL(pcie_walk_rcec, "CXL");
>>  
>>  void pci_rcec_init(struct pci_dev *dev)
>>  {
>> diff --git a/include/linux/aer.h b/include/linux/aer.h
>> index f8eb32805957..1f79f0be4bf7 100644
>> --- a/include/linux/aer.h
>> +++ b/include/linux/aer.h
>> @@ -66,12 +66,14 @@ struct cxl_proto_err_work_data {
>>  
>>  #if defined(CONFIG_PCIEAER)
>>  int pci_aer_clear_nonfatal_status(struct pci_dev *dev);
>> +void pci_aer_clear_fatal_status(struct pci_dev *dev);
>>  int pcie_aer_is_native(struct pci_dev *dev);
>>  #else
>>  static inline int pci_aer_clear_nonfatal_status(struct pci_dev *dev)
>>  {
>>  	return -EINVAL;
>>  }
>> +static inline void pci_aer_clear_fatal_status(struct pci_dev *dev) { }
>>  static inline int pcie_aer_is_native(struct pci_dev *dev) { return 0; }
>>  #endif
>>  
>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>> index 3dcab36c437f..3407d687459d 100644
>> --- a/include/linux/pci.h
>> +++ b/include/linux/pci.h
>> @@ -1804,6 +1804,9 @@ extern bool pcie_ports_native;
>>  
>>  int pcie_set_target_speed(struct pci_dev *port, enum pci_bus_speed speed_req,
>>  			  bool use_lt);
>> +void pcie_walk_rcec(struct pci_dev *rcec,
>> +		    int (*cb)(struct pci_dev *, void *),
>> +		    void *userdata);
>>  #else
>>  #define pcie_ports_disabled	true
>>  #define pcie_ports_native	false
>> @@ -1814,8 +1817,15 @@ static inline int pcie_set_target_speed(struct pci_dev *port,
>>  {
>>  	return -EOPNOTSUPP;
>>  }
>> +
>> +static inline void pcie_walk_rcec(struct pci_dev *rcec,
>> +				  int (*cb)(struct pci_dev *, void *),
>> +				  void *userdata) { }
>> +
>>  #endif
>>  
>> +void pcie_clear_device_status(struct pci_dev *dev);
>> +
>>  #define PCIE_LINK_STATE_L0S		(BIT(0) | BIT(1)) /* Upstr/dwnstr L0s */
>>  #define PCIE_LINK_STATE_L1		BIT(2)	/* L1 state */
>>  #define PCIE_LINK_STATE_L1_1		BIT(3)	/* ASPM L1.1 state */