Re: [RESEND v13 23/25] CXL/PCI: Introduce CXL uncorrectable protocol error recovery

Dave Jiang
2025-11-04T23:43:52Z

On 11/4/25 11:47 AM, Jonathan Cameron wrote:
> On Tue, 4 Nov 2025 11:03:03 -0600
> Terry Bowman <terry.bowman@amd.com> wrote:
>
>> Implement cxl_do_recovery() to handle uncorrectable protocol
>> errors (UCE), following the design of pcie_do_recovery(). Unlike PCIe,
>> all CXL UCEs are treated as fatal and trigger a kernel panic to avoid
>> potential CXL memory corruption.
>>
>> Add cxl_walk_port(), analogous to pci_walk_bridge(), to traverse the
>> CXL topology from the error source through downstream CXL ports and
>> endpoints.
>>
>> Introduce cxl_report_error_detected(), mirroring PCI's
>> report_error_detected(), and implement device locking for the affected
>> subtree. Endpoints require locking the PCI device (pdev->dev) and the
>> CXL memdev (cxlmd->dev). CXL ports require locking the PCI
>> device (pdev->dev) and the parent CXL port.
>>
>> The device locks should be taken early where possible. The initially
>> reporting device will be locked after kfifo dequeue. Iterated devices
>> will be locked in cxl_report_error_detected() and must lock the
>> iterated devices except for the first device as it has already been
>> locked.
>>
>> Export pci_aer_clear_fatal_status() for use when a UCE is not present.
>>
>> Signed-off-by: Terry Bowman <terry.bowman@amd.com>
>
> Follow on comments around the locking stuff. If that has been there
> a while and I didn't notice before, sorry!
>
>>
>> ---
>>
>> Changes in v12->v13:
>> - Add guard() before calling cxl_pci_drv_bound() (Dave Jiang)
>> - Add guard() calls for EP (cxlds->cxlmd->dev & pdev->dev) and ports
>> (pdev->dev & parent cxl_port) in cxl_report_error_detected() and
>> cxl_handle_proto_error() (Terry)
>> - Remove unnecessary check for endpoint port. (Dave Jiang)
>> - Remove check for RCIEP EP in cxl_report_error_detected(). (Terry)
>>
>> Changes in v11->v12:
>> - Clean up port discovery in cxl_do_recovery() (Dave)
>> - Add PCI_EXP_TYPE_RC_END to type check in cxl_report_error_detected()
>>
>> Changes in v10->v11:
>> - pci_ers_merge_results() - Move to earlier patch
>> ---
>> drivers/cxl/core/ras.c | 135 ++++++++++++++++++++++++++++++++++++++++-
>> drivers/pci/pci.h | 1 -
>> drivers/pci/pcie/aer.c | 1 +
>> include/linux/aer.h | 2 +
>> 4 files changed, 135 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/cxl/core/ras.c b/drivers/cxl/core/ras.c
>> index 5bc144cde0ee..52c6f19564b6 100644
>> --- a/drivers/cxl/core/ras.c
>> +++ b/drivers/cxl/core/ras.c
>> @@ -259,8 +259,138 @@ static void device_unlock_if(struct device *dev, bool take)
>> device_unlock(dev);
>> }
>>
>> +/**
>> + * cxl_report_error_detected
>> + * @dev: Device being reported
>> + * @data: Result
>> + * @err_pdev: Device with initial detected error. Is locked immediately
>> + * after KFIFO dequeue.
>> + */
>> +static int cxl_report_error_detected(struct device *dev, void *data, struct pci_dev *err_pdev)
>> +{
>> + bool need_lock = (dev != &err_pdev->dev);
>
> Add a comment on why this controls need for locking.
> The resulting code is complex enough I'd be tempted to split the whole
> thing into locked and unlocked variants.

May not be a bad idea. Terry, can you see if this would reduce the complexity?

DJ

>
>> + pci_ers_result_t vote, *result = data;
>> + struct pci_dev *pdev;
>> +
>> + if (!dev || !dev_is_pci(dev))
>> + return 0;
>> + pdev = to_pci_dev(dev);
>> +
>> + device_lock_if(&pdev->dev, need_lock);
>> + if (is_pcie_endpoint(pdev) && !cxl_pci_drv_bound(pdev)) {
>> + device_unlock_if(&pdev->dev, need_lock);
>> + return PCI_ERS_RESULT_NONE;
>> + }
>> +
>> + if (pdev->aer_cap)
>> + pci_clear_and_set_config_dword(pdev,
>> + pdev->aer_cap + PCI_ERR_COR_STATUS,
>> + 0, PCI_ERR_COR_INTERNAL);
>> +
>> + if (is_pcie_endpoint(pdev)) {
>> + struct cxl_dev_state *cxlds = pci_get_drvdata(pdev);
>> +
>> + device_lock_if(&cxlds->cxlmd->dev, need_lock);
>> + vote = cxl_error_detected(&cxlds->cxlmd->dev);
>> + device_unlock_if(&cxlds->cxlmd->dev, need_lock);
>> + } else {
>> + vote = cxl_port_error_detected(dev);
>> + }
>> +
>> + pcie_clear_device_status(pdev);
>> + *result = pcie_ers_merge_result(*result, vote);
>> + device_unlock_if(&pdev->dev, need_lock);
>> +
>> + return 0;
>> +}
>
>> +
>> +/**
>> + * cxl_walk_port
> Needs a short description I think to count as valid kernel-doc and
> stop the tool moaning if anyone runs it on this.
>
>> + *
>> + * @port: Port be traversed into
>> + * @cb: Callback for handling the CXL Ports
>> + * @userdata: Result
>> + * @err_pdev: Device with initial detected error. Is locked immediately
>> + * after KFIFO dequeue.
>> + */
>> +static void cxl_walk_port(struct cxl_port *port,
>> + int (*cb)(struct device *, void *, struct pci_dev *),
>> + void *userdata,
>> + struct pci_dev *err_pdev)
>> +{
>> + struct cxl_port *err_port __free(put_cxl_port) = get_cxl_port(err_pdev);
>> + bool need_lock = (port != err_port);
>> + struct cxl_dport *dport = NULL;
>> + unsigned long index;
>> +
>> + device_lock_if(&port->dev, need_lock);
>> + if (is_cxl_endpoint(port)) {
>> + cb(port->uport_dev->parent, userdata, err_pdev);
>> + device_unlock_if(&port->dev, need_lock);
>> + return;
>> + }
>> +
>> + if (port->uport_dev && dev_is_pci(port->uport_dev))
>> + cb(port->uport_dev, userdata, err_pdev);
>> +
>> + /*
>> + * Iterate over the set of Downstream Ports recorded in port->dports (XArray):
>> + * - For each dport, attempt to find a child CXL Port whose parent dport
>> + * match.
>> + * - Invoke the provided callback on the dport's device.
>> + * - If a matching child CXL Port device is found, recurse into that port to
>> + * continue the walk.
>> + */
>> + xa_for_each(&port->dports, index, dport)
>> + {
>
> Move that to line above for normal kernel loop formatting.
>
> xa_for_each(&port->dports, index, dport) {
>
>> + struct device *child_port_dev __free(put_device) =
>> + bus_find_device(&cxl_bus_type, &port->dev, dport->dport_dev,
>> + match_port_by_parent_dport);
>> +
>> + cb(dport->dport_dev, userdata, err_pdev);
>> + if (child_port_dev)
>> + cxl_walk_port(to_cxl_port(child_port_dev), cb, userdata, err_pdev);
>> + }
>> + device_unlock_if(&port->dev, need_lock);
>> +}
>> +
>
>>
>> void cxl_handle_cor_ras(struct device *dev, u64 serial, void __iomem *ras_base)
>> @@ -483,16 +613,15 @@ static void cxl_proto_err_work_fn(struct work_struct *work)
>> if (!cxl_pci_drv_bound(pdev))
>> return;
>> cxlmd_dev = &cxlds->cxlmd->dev;
>> - device_lock_if(cxlmd_dev, cxlmd_dev);
>> } else {
>> cxlmd_dev = NULL;
>> }
>>
>> + /* Lock the CXL parent Port */
>> struct cxl_port *port __free(put_cxl_port) = get_cxl_port(pdev);
>> - if (!port)
>> - return;
>> guard(device)(&port->dev);
>>
>> + device_lock_if(cxlmd_dev, cxlmd_dev);
>> cxl_handle_proto_error(&wd);
>> device_unlock_if(cxlmd_dev, cxlmd_dev);
> Same issue on these helpers, but I'm also not sure why moving them in this
> patch makes sense. I'm not sure what changed.
>
> Perhaps this is stuff that ended up in wrong patch?
>> }
>
>