Re: [PATCH v11 21/23] CXL/PCI: Introduce CXL uncorrectable protocol error recovery

Dave Jiang
2025-09-03T22:30:43Z

On 8/26/25 6:35 PM, Terry Bowman wrote:
> Populate the cxl_do_recovery() function with uncorrectable protocol error (UCE)
> handling. Follow similar design as found in PCIe error driver,
> pcie_do_recovery(). One difference is cxl_do_recovery() will treat all UCEs
> as fatal with a kernel panic. This is to prevent corruption on CXL memory.
>
> Introduce cxl_walk_port(). Make this analogous to pci_walk_bridge() but walking
> CXL ports instead. This will iterate through the CXL topology from the
> erroring device through the downstream CXL Ports and Endpoints.
>
> Export pci_aer_clear_fatal_status() for CXL to use if a UCE is not found.
>
> Signed-off-by: Terry Bowman <terry.bowman@amd.com>
>
> ---
> Changes in v10->v11:
> - pci_ers_merge_results() - Move to earlier patch
> ---
> drivers/cxl/core/port.c | 1 +
> drivers/cxl/core/ras.c | 94 +++++++++++++++++++++++++++++++++++++++++
> drivers/pci/pci.h | 2 -
> include/linux/aer.h | 2 +
> 4 files changed, 97 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> index 758fb73374c1..085c8620a797 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -1347,6 +1347,7 @@ struct cxl_port *find_cxl_port(struct device *dport_dev,
> port = __find_cxl_port(&ctx);
> return port;
> }
> +EXPORT_SYMBOL_NS_GPL(find_cxl_port, "CXL");
>
> static struct cxl_port *find_cxl_port_at(struct cxl_port *parent_port,
> struct device *dport_dev,
> diff --git a/drivers/cxl/core/ras.c b/drivers/cxl/core/ras.c
> index 536ca9c815ce..3da675f72616 100644
> --- a/drivers/cxl/core/ras.c
> +++ b/drivers/cxl/core/ras.c
> @@ -6,6 +6,7 @@
> #include <cxl/event.h>
> #include <cxlmem.h>
> #include <cxlpci.h>
> +#include <cxl.h>
> #include "trace.h"
>
> static void cxl_cper_trace_corr_port_prot_err(struct pci_dev *pdev,
> @@ -468,8 +469,101 @@ void cxl_endpoint_port_init_ras(struct cxl_port *ep)
> }
> EXPORT_SYMBOL_NS_GPL(cxl_endpoint_port_init_ras, "CXL");
>
> +static int cxl_report_error_detected(struct device *dev, void *data)
> +{
> + struct pci_dev *pdev = to_pci_dev(dev);
> + pci_ers_result_t vote, *result = data;
> +
> + guard(device)(dev);
> +
> + if (pci_pcie_type(pdev) == PCI_EXP_TYPE_ENDPOINT)
> + vote = cxl_error_detected(dev);
> + else
> + vote = cxl_port_error_detected(dev);
> +
> + vote = cxl_error_detected(dev);
> + *result = pci_ers_merge_result(*result, vote);
> +
> + return 0;
> +}
> +
> +static int match_port_by_parent_dport(struct device *dev, const void *dport_dev)
> +{
> + struct cxl_port *port;
> +
> + if (!is_cxl_port(dev))
> + return 0;
> +
> + port = to_cxl_port(dev);
> +
> + return port->parent_dport->dport_dev == dport_dev;
> +}
> +
> +static void cxl_walk_port(struct device *port_dev,
> + int (*cb)(struct device *, void *),
> + void *userdata)
> +{
> + struct cxl_dport *dport = NULL;
> + struct cxl_port *port;
> + unsigned long index;
> +
> + if (!port_dev)
> + return;
> +
> + port = to_cxl_port(port_dev);
> + if (port->uport_dev && dev_is_pci(port->uport_dev))
> + cb(port->uport_dev, userdata);
> +
> + xa_for_each(&port->dports, index, dport)
> + {
> + struct device *child_port_dev __free(put_device) =
> + bus_find_device(&cxl_bus_type, &port->dev, dport,
> + match_port_by_parent_dport);
> +
> + cb(dport->dport_dev, userdata);
> +
> + cxl_walk_port(child_port_dev, cxl_report_error_detected, userdata);
> + }
> +
> + if (is_cxl_endpoint(port))
> + cb(port->uport_dev->parent, userdata);
> +}
> +
> static void cxl_do_recovery(struct device *dev)
> {
> + pci_ers_result_t status = PCI_ERS_RESULT_CAN_RECOVER;
> + struct pci_dev *pdev = to_pci_dev(dev);
> + struct cxl_dport *dport;
> + struct cxl_port *port;
> +
> + if ((pci_pcie_type(pdev) == PCI_EXP_TYPE_ROOT_PORT) ||
> + (pci_pcie_type(pdev) == PCI_EXP_TYPE_DOWNSTREAM)) {
> + port = find_cxl_port(&pdev->dev, &dport);
> + } else if (pci_pcie_type(pdev) == PCI_EXP_TYPE_UPSTREAM) {
> + struct device *port_dev = bus_find_device(&cxl_bus_type, NULL,
> + &pdev->dev, match_uport);
> + port = to_cxl_port(port_dev);
> + }

Do we not attempt recovery if the device is an endpoint? Is it because it is handled directly by AER callback of the cxl_pci driver? Should endpoint error just not be forwarded from the AER kfifo producer instead of being checked on the consumer end after going through the kfifo mechanism?

DJ

> +
> + if (!port)
> + return;
> +
> + cxl_walk_port(&port->dev, cxl_report_error_detected, &status);
> + if (status == PCI_ERS_RESULT_PANIC)
> + panic("CXL cachemem error.");
> +
> + /*
> + * If we have native control of AER, clear error status in the device
> + * that detected the error. If the platform retained control of AER,
> + * it is responsible for clearing this status. In that case, the
> + * signaling device may not even be visible to the OS.
> + */
> + if (cxl_error_is_native(pdev)) {
> + pcie_clear_device_status(pdev);
> + pci_aer_clear_nonfatal_status(pdev);
> + pci_aer_clear_fatal_status(pdev);
> + }
> + put_device(&port->dev);
> }
>
> static void cxl_handle_cor_ras(struct device *dev, u64 serial, void __iomem *ras_base)
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 69ff7c2d214f..0c4f73dd645f 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -1170,13 +1170,11 @@ static inline void cxl_rch_enable_rcec(struct pci_dev *rcec) { }
>
> #ifdef CONFIG_CXL_RAS
> void pci_aer_unmask_internal_errors(struct pci_dev *dev);
> -bool cxl_error_is_native(struct pci_dev *dev);
> bool is_internal_error(struct aer_err_info *info);
> bool is_cxl_error(struct pci_dev *pdev, struct aer_err_info *info);
> void cxl_forward_error(struct pci_dev *pdev, struct aer_err_info *info);
> #else
> static inline void pci_aer_unmask_internal_errors(struct pci_dev *dev) { }
> -static inline bool cxl_error_is_native(struct pci_dev *dev) { return false; }
> static inline bool is_internal_error(struct aer_err_info *info) { return false; }
> static inline bool is_cxl_error(struct pci_dev *pdev, struct aer_err_info *info) { return false; }
> static inline void cxl_forward_error(struct pci_dev *pdev, struct aer_err_info *info) { }
> diff --git a/include/linux/aer.h b/include/linux/aer.h
> index 1f79f0be4bf7..751a026fea73 100644
> --- a/include/linux/aer.h
> +++ b/include/linux/aer.h
> @@ -81,10 +81,12 @@ static inline int pcie_aer_is_native(struct pci_dev *dev) { return 0; }
> int cxl_proto_err_kfifo_get(struct cxl_proto_err_work_data *wd);
> void cxl_register_proto_err_work(struct work_struct *work);
> void cxl_unregister_proto_err_work(void);
> +bool cxl_error_is_native(struct pci_dev *dev);
> #else
> static inline int cxl_proto_err_kfifo_get(struct cxl_proto_err_work_data *wd) { return 0; }
> static inline void cxl_register_proto_err_work(struct work_struct *work) { }
> static inline void cxl_unregister_proto_err_work(void) { }
> +static inline bool cxl_error_is_native(struct pci_dev *dev) { return false; }
> #endif
>
> void pci_print_aer(struct pci_dev *dev, int aer_severity,