Re: [PATCH v9 03/16] CXL/AER: Introduce kfifo for forwarding CXL errors

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

On 6/4/2025 5:50 PM, Sathyanarayanan Kuppuswamy wrote:
> On 6/3/25 10:22 AM, Terry Bowman wrote:
>> CXL error handling will soon be moved from the AER driver into the CXL
>> driver. This requires a notification mechanism for the AER driver to share
>> the AER interrupt with the CXL driver. The notification will be used
>> as an indication for the CXL drivers to handle and log the CXL RAS errors.
>>
>> Add a kfifo work queue to be used by the AER driver and CXL driver. The AER
>> driver will be the sole kfifo producer adding work and the cxl_core will be
>> the sole kfifo consumer removing work. Add the boilerplate kfifo support.
>>
>> Add CXL work queue handler registration functions in the AER driver. Export
>> the functions allowing CXL driver to access. Implement registration
>> functions for the CXL driver to assign or clear the work handler function.
>>
>> Introduce function cxl_create_prot_err_info() and 'struct cxl_prot_err_info'.
>> Implement cxl_create_prot_err_info() to populate a 'struct cxl_prot_err_info'
>> instance with the AER severity and the erring device's PCI SBDF. The SBDF
>> details will be used to rediscover the erring device after the CXL driver
>> dequeues the kfifo work. The device rediscovery will be introduced along
>> with the CXL handling in future patches.
>>
>> Signed-off-by: Terry Bowman <terry.bowman@amd.com>
>> ---
>>   drivers/cxl/core/ras.c |  31 +++++++++-
>>   drivers/cxl/cxlpci.h   |   1 +
>>   drivers/pci/pcie/aer.c | 132 ++++++++++++++++++++++++++++-------------
>>   include/linux/aer.h    |  36 +++++++++++
>>   4 files changed, 157 insertions(+), 43 deletions(-)
>>
>> diff --git a/drivers/cxl/core/ras.c b/drivers/cxl/core/ras.c
>> index 485a831695c7..d35525e79e04 100644
>> --- a/drivers/cxl/core/ras.c
>> +++ b/drivers/cxl/core/ras.c
>> @@ -5,6 +5,7 @@
>>   #include <linux/aer.h>
>>   #include <cxl/event.h>
>>   #include <cxlmem.h>
>> +#include <cxlpci.h>
>>   #include "trace.h"
>>   
>>   static void cxl_cper_trace_corr_port_prot_err(struct pci_dev *pdev,
>> @@ -107,13 +108,41 @@ 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);
>>   
>> +#ifdef CONFIG_PCIEAER_CXL
>> +
>> +static void cxl_prot_err_work_fn(struct work_struct *work)
>> +{
>> +}
>> +
>> +#else
>> +static void cxl_prot_err_work_fn(struct work_struct *work) { }
>> +#endif /* CONFIG_PCIEAER_CXL */
>> +
>> +static struct work_struct cxl_prot_err_work;
>> +static DECLARE_WORK(cxl_prot_err_work, cxl_prot_err_work_fn);
>> +
>>   int cxl_ras_init(void)
>>   {
>> -	return cxl_cper_register_prot_err_work(&cxl_cper_prot_err_work);
>> +	int rc;
>> +
>> +	rc = cxl_cper_register_prot_err_work(&cxl_cper_prot_err_work);
>> +	if (rc)
>> +		pr_err("Failed to register CPER AER kfifo (%x)", rc);
>> +
>> +	rc = cxl_register_prot_err_work(&cxl_prot_err_work);
>> +	if (rc) {
>> +		pr_err("Failed to register native AER kfifo (%x)", rc);
>> +		return rc;
>> +	}
>> +
>> +	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_prot_err_work();
>> +	cancel_work_sync(&cxl_prot_err_work);
>>   }
>> diff --git a/drivers/cxl/cxlpci.h b/drivers/cxl/cxlpci.h
>> index 54e219b0049e..6f1396ef7b77 100644
>> --- a/drivers/cxl/cxlpci.h
>> +++ b/drivers/cxl/cxlpci.h
>> @@ -4,6 +4,7 @@
>>   #define __CXL_PCI_H__
>>   #include <linux/pci.h>
>>   #include "cxl.h"
>> +#include "linux/aer.h"
>>   
>>   #define CXL_MEMORY_PROGIF	0x10
>>   
>> diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
>> index adb4b1123b9b..5350fa5be784 100644
>> --- a/drivers/pci/pcie/aer.c
>> +++ b/drivers/pci/pcie/aer.c
>> @@ -114,6 +114,14 @@ struct aer_stats {
>>   static int pcie_aer_disable;
>>   static pci_ers_result_t aer_root_reset(struct pci_dev *dev);
>>   
>> +#if defined(CONFIG_PCIEAER_CXL)
>> +#define CXL_ERROR_SOURCES_MAX          128
>> +static DEFINE_KFIFO(cxl_prot_err_fifo, struct cxl_prot_err_work_data,
>> +		    CXL_ERROR_SOURCES_MAX);
>> +static DEFINE_SPINLOCK(cxl_prot_err_fifo_lock);
>> +struct work_struct *cxl_prot_err_work;
>> +#endif
>> +
>>   void pci_no_aer(void)
>>   {
>>   	pcie_aer_disable = 1;
>> @@ -1004,45 +1012,17 @@ static bool is_internal_error(struct aer_err_info *info)
>>   	return info->status & PCI_ERR_UNC_INTN;
>>   }
>>   
>> -static int cxl_rch_handle_error_iter(struct pci_dev *dev, void *data)
>> +static bool is_cxl_error(struct pci_dev *pdev, struct aer_err_info *info)
>>   {
>> -	struct aer_err_info *info = (struct aer_err_info *)data;
>> -	const struct pci_error_handlers *err_handler;
>> +	if (!info || !info->is_cxl)
>> +		return false;
>>   
>> -	if (!is_cxl_mem_dev(dev) || !cxl_error_is_native(dev))
>> -		return 0;
>> +	/* Only CXL Endpoints are currently supported */
>> +	if ((pci_pcie_type(pdev) != PCI_EXP_TYPE_ENDPOINT) &&
>> +	    (pci_pcie_type(pdev) != PCI_EXP_TYPE_RC_EC))
>> +		return false;
>>   
>> -	/* Protect dev->driver */
>> -	device_lock(&dev->dev);
>> -
>> -	err_handler = dev->driver ? dev->driver->err_handler : NULL;
>> -	if (!err_handler)
>> -		goto out;
>> -
>> -	if (info->severity == AER_CORRECTABLE) {
>> -		if (err_handler->cor_error_detected)
>> -			err_handler->cor_error_detected(dev);
>> -	} else if (err_handler->error_detected) {
>> -		if (info->severity == AER_NONFATAL)
>> -			err_handler->error_detected(dev, pci_channel_io_normal);
>> -		else if (info->severity == AER_FATAL)
>> -			err_handler->error_detected(dev, pci_channel_io_frozen);
>> -	}
>> -out:
>> -	device_unlock(&dev->dev);
>> -	return 0;
>> -}
>> -
>> -static void cxl_rch_handle_error(struct pci_dev *dev, struct aer_err_info *info)
>> -{
>> -	/*
>> -	 * Internal errors of an RCEC indicate an AER error in an
>> -	 * RCH's downstream port. Check and handle them in the CXL.mem
>> -	 * device driver.
>> -	 */
>> -	if (pci_pcie_type(dev) == PCI_EXP_TYPE_RC_EC &&
>> -	    is_internal_error(info))
>> -		pcie_walk_rcec(dev, cxl_rch_handle_error_iter, info);
>> +	return is_internal_error(info);
>>   }
>>   
>>   static int handles_cxl_error_iter(struct pci_dev *dev, void *data)
>> @@ -1056,13 +1036,17 @@ static int handles_cxl_error_iter(struct pci_dev *dev, void *data)
>>   	return *handles_cxl;
>>   }
>>   
>> -static bool handles_cxl_errors(struct pci_dev *rcec)
>> +static bool handles_cxl_errors(struct pci_dev *dev)
>>   {
>>   	bool handles_cxl = false;
>>   
>> -	if (pci_pcie_type(rcec) == PCI_EXP_TYPE_RC_EC &&
>> -	    pcie_aer_is_native(rcec))
>> -		pcie_walk_rcec(rcec, handles_cxl_error_iter, &handles_cxl);
>> +	if (!pcie_aer_is_native(dev))
>> +		return false;
>> +
>> +	if (pci_pcie_type(dev) == PCI_EXP_TYPE_RC_EC)
>> +		pcie_walk_rcec(dev, handles_cxl_error_iter, &handles_cxl);
>> +	else
>> +		handles_cxl = pcie_is_cxl(dev);
>>   
>>   	return handles_cxl;
>>   }
>> @@ -1076,10 +1060,46 @@ static void cxl_rch_enable_rcec(struct pci_dev *rcec)
>>   	pci_info(rcec, "CXL: Internal errors unmasked");
>>   }
>>   
>> +static int cxl_create_prot_error_info(struct pci_dev *pdev,
>> +				      struct aer_err_info *aer_err_info,
>> +				      struct cxl_prot_error_info *cxl_err_info)
>> +{
>> +	cxl_err_info->severity = aer_err_info->severity;
>> +
>> +	cxl_err_info->function = PCI_FUNC(pdev->devfn);
>> +	cxl_err_info->device = PCI_SLOT(pdev->devfn);
>> +	cxl_err_info->bus = pdev->bus->number;
>> +	cxl_err_info->segment = pci_domain_nr(pdev->bus);
>> +
>> +	return 0;
>> +}
>> +
>> +static void forward_cxl_error(struct pci_dev *pdev, struct aer_err_info *aer_err_info)
>> +{
>> +	struct cxl_prot_err_work_data wd;
>> +	struct cxl_prot_error_info *cxl_err_info = &wd.err_info;
>> +
>> +	cxl_create_prot_error_info(pdev, aer_err_info, cxl_err_info);
>> +
>> +	if (!kfifo_put(&cxl_prot_err_fifo, wd)) {
>> +		dev_err_ratelimited(&pdev->dev, "CXL kfifo overflow\n");
>> +		return;
>> +	}
>> +
>> +	schedule_work(cxl_prot_err_work);
>> +}
>> +
>>   #else
>>   static inline void cxl_rch_enable_rcec(struct pci_dev *dev) { }
>>   static inline void cxl_rch_handle_error(struct pci_dev *dev,
>>   					struct aer_err_info *info) { }
>> +static inline void forward_cxl_error(struct pci_dev *dev,
>> +				    struct aer_err_info *info) { }
>> +static inline bool handles_cxl_errors(struct pci_dev *dev)
>> +{
>> +	return false;
>> +}
>> +static bool is_cxl_error(struct pci_dev *pdev, struct aer_err_info *info) { return 0; };
>>   #endif
>>   
>>   /**
>> @@ -1117,8 +1137,11 @@ static void pci_aer_handle_error(struct pci_dev *dev, struct aer_err_info *info)
>>   
>>   static void handle_error_source(struct pci_dev *dev, struct aer_err_info *info)
>>   {
>> -	cxl_rch_handle_error(dev, info);
>> -	pci_aer_handle_error(dev, info);
>> +	if (is_cxl_error(dev, info))
>> +		forward_cxl_error(dev, info);
>> +	else
>> +		pci_aer_handle_error(dev, info);
>> +
>>   	pci_dev_put(dev);
>>   }
>>   
>> @@ -1582,6 +1605,31 @@ static pci_ers_result_t aer_root_reset(struct pci_dev *dev)
>>   	return rc ? PCI_ERS_RESULT_DISCONNECT : PCI_ERS_RESULT_RECOVERED;
>>   }
>>   
>> +#if defined(CONFIG_PCIEAER_CXL)
>> +
>> +int cxl_register_prot_err_work(struct work_struct *work)
>> +{
>> +	guard(spinlock)(&cxl_prot_err_fifo_lock);
>> +	cxl_prot_err_work = work;
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL_NS_GPL(cxl_register_prot_err_work, "CXL");
>> +
>> +int cxl_unregister_prot_err_work(void)
>> +{
>> +	guard(spinlock)(&cxl_prot_err_fifo_lock);
>> +	cxl_prot_err_work = NULL;
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL_NS_GPL(cxl_unregister_prot_err_work, "CXL");
>> +
> Above two functions can never fail, right? What not make them return void?

You are correct. Good point. Thanks, I'll make the change.

Terry
>> +int cxl_prot_err_kfifo_get(struct cxl_prot_err_work_data *wd)
>> +{
>> +	return kfifo_get(&cxl_prot_err_fifo, wd);
>> +}
>> +EXPORT_SYMBOL_NS_GPL(cxl_prot_err_kfifo_get, "CXL");
>> +#endif
>> +
>>   static struct pcie_port_service_driver aerdriver = {
>>   	.name		= "aer",
>>   	.port_type	= PCIE_ANY_PORT,
>> diff --git a/include/linux/aer.h b/include/linux/aer.h
>> index 02940be66324..550407240ab5 100644
>> --- a/include/linux/aer.h
>> +++ b/include/linux/aer.h
>> @@ -10,6 +10,7 @@
>>   
>>   #include <linux/errno.h>
>>   #include <linux/types.h>
>> +#include <linux/workqueue_types.h>
>>   
>>   #define AER_NONFATAL			0
>>   #define AER_FATAL			1
>> @@ -53,6 +54,27 @@ struct aer_capability_regs {
>>   	u16 uncor_err_source;
>>   };
>>   
>> +/**
>> + * struct cxl_prot_err_info - Error information used in CXL error handling
>> + * @severity: AER severity
>> + * @function: Device's PCI function
>> + * @device: Device's PCI device
>> + * @bus: Device's PCI bus
>> + * @segment: Device's PCI segment
>> + */
>> +struct cxl_prot_error_info {
>> +	int severity;
>> +
>> +	u8 function;
>> +	u8 device;
>> +	u8 bus;
>> +	u16 segment;
>> +};
>> +
>> +struct cxl_prot_err_work_data {
>> +	struct cxl_prot_error_info err_info;
>> +};
>> +
>>   #if defined(CONFIG_PCIEAER)
>>   int pci_aer_clear_nonfatal_status(struct pci_dev *dev);
>>   int pcie_aer_is_native(struct pci_dev *dev);
>> @@ -64,6 +86,20 @@ static inline int pci_aer_clear_nonfatal_status(struct pci_dev *dev)
>>   static inline int pcie_aer_is_native(struct pci_dev *dev) { return 0; }
>>   #endif
>>   
>> +#if defined(CONFIG_PCIEAER_CXL)
>> +int cxl_register_prot_err_work(struct work_struct *work);
>> +int cxl_unregister_prot_err_work(void);
>> +int cxl_prot_err_kfifo_get(struct cxl_prot_err_work_data *wd);
>> +#else
>> +static inline int
>> +cxl_register_prot_err_work(struct work_struct *work)
>> +{
>> +	return 0;
>> +}
>> +static inline int cxl_unregister_prot_err_work(void) { return 0; }
>> +static inline int cxl_prot_err_kfifo_get(struct cxl_prot_err_work_data *wd) { return 0; }
>> +#endif
>> +
>>   void pci_print_aer(struct pci_dev *dev, int aer_severity,
>>   		    struct aer_capability_regs *aer);
>>   int cper_severity_to_aer(int cper_severity);