Re: [PATCH v4 07/15] PCI/AER: Add CXL PCIe Port Uncorrectable Error recovery in AER service driver

[Alejandro Lucero Palau <alucerop@amd.com>]

On 12/11/24 23:39, Terry Bowman wrote:
> Existing recovery procedure for PCIe Uncorrectable Errors (UCE) does not
> apply to CXL devices. Recovery can not be used for CXL devices because of
> potential corruption on what can be system memory. Also, current PCIe UCE
> recovery, in the case of a Root Port (RP) or Downstream Switch Port (DSP),
> does not begin at the RP/DSP but begins at the first downstream device.
> This will miss handling CXL Protocol Errors in a CXL RP or DSP. A separate
> CXL recovery is needed because of the different handling requirements
>
> Add a new function, cxl_do_recovery() using the following.
>
> Add cxl_walk_bridge() to iterate the detected error's sub-topology.
> cxl_walk_bridge() is similar to pci_walk_bridge() but the CXL flavor
> will begin iteration at the RP or DSP rather than beginning at the
> first downstream device.
>
> Add cxl_report_error_detected() as an analog to report_error_detected().
> It will call pci_driver::cxl_err_handlers for each iterated downstream
> device. The pci_driver::cxl_err_handler's UCE handler returns a boolean
> indicating if there was a UCE error detected during handling.
>
> cxl_do_recovery() uses the status from cxl_report_error_detected() to
> determine how to proceed. Non-fatal CXL UCE errors will be treated as
> fatal. If a UCE was present during handling then cxl_do_recovery()
> will kernel panic.
>
> Signed-off-by: Terry Bowman <terry.bowman@amd.com>
> ---
>   drivers/pci/pci.h      |  3 +++
>   drivers/pci/pcie/aer.c |  4 ++++
>   drivers/pci/pcie/err.c | 54 ++++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 61 insertions(+)
>
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 14d00ce45bfa..5a67e41919d8 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -658,6 +658,9 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>   		pci_channel_state_t state,
>   		pci_ers_result_t (*reset_subordinates)(struct pci_dev *pdev));
>   
> +/* CXL error reporting and handling */
> +void cxl_do_recovery(struct pci_dev *dev);
> +
>   bool pcie_wait_for_link(struct pci_dev *pdev, bool active);
>   int pcie_retrain_link(struct pci_dev *pdev, bool use_lt);
>   
> diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
> index c1eb939c1cca..861521872318 100644
> --- a/drivers/pci/pcie/aer.c
> +++ b/drivers/pci/pcie/aer.c
> @@ -1024,6 +1024,8 @@ static int cxl_rch_handle_error_iter(struct pci_dev *dev, void *data)
>   			err_handler->error_detected(dev, pci_channel_io_normal);
>   		else if (info->severity == AER_FATAL)
>   			err_handler->error_detected(dev, pci_channel_io_frozen);
> +
> +		cxl_do_recovery(dev);
>   	}
>   out:
>   	device_unlock(&dev->dev);
> @@ -1048,6 +1050,8 @@ static void cxl_handle_error(struct pci_dev *dev, struct aer_err_info *info)
>   			pdrv->cxl_err_handler->cor_error_detected(dev);
>   
>   		pcie_clear_device_status(dev);
> +	} else {
> +		cxl_do_recovery(dev);
>   	}
>   }
>   
> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
> index 31090770fffc..6f7cf5e0087f 100644
> --- a/drivers/pci/pcie/err.c
> +++ b/drivers/pci/pcie/err.c
> @@ -276,3 +276,57 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>   
>   	return status;
>   }
> +
> +static void cxl_walk_bridge(struct pci_dev *bridge,
> +			    int (*cb)(struct pci_dev *, void *),
> +			    void *userdata)
> +{
> +	bool *status = userdata;
> +
> +	cb(bridge, status);
> +	if (bridge->subordinate && !*status)


I would prefer to use not a pointer for status as you are not changing 
what it points to here, so first a cast then using just !status in the 
conditional.


> +		pci_walk_bus(bridge->subordinate, cb, status);
> +}
> +
> +static int cxl_report_error_detected(struct pci_dev *dev, void *data)
> +{
> +	struct pci_driver *pdrv = dev->driver;
> +	bool *status = data;
> +
> +	device_lock(&dev->dev);
> +	if (pdrv && pdrv->cxl_err_handler &&
> +	    pdrv->cxl_err_handler->error_detected) {
> +		const struct cxl_error_handlers *cxl_err_handler =
> +			pdrv->cxl_err_handler;
> +		*status |= cxl_err_handler->error_detected(dev);


This implies status should not be a bool pointer as different bits can 
be set by the returning value, but as the code seems to only care about 
any bit implying an error and therefore error detected, I guess that is 
fine. However, the next function calling this one is using an int ...


Confusing to me. I would expect here not an OR but returning just when a 
first error is detected, handling the lock properly, with the walk 
function behind the scenes breaking the walk if the return is anything 
other than zero.


> +	}
> +	device_unlock(&dev->dev);
> +	return *status;
> +}
> +
> +void cxl_do_recovery(struct pci_dev *dev)
> +{
> +	struct pci_host_bridge *host = pci_find_host_bridge(dev->bus);
> +	int type = pci_pcie_type(dev);
> +	struct pci_dev *bridge;
> +	int status;
> +
> +	if (type == PCI_EXP_TYPE_ROOT_PORT ||
> +	    type == PCI_EXP_TYPE_DOWNSTREAM ||
> +	    type == PCI_EXP_TYPE_UPSTREAM ||
> +	    type == PCI_EXP_TYPE_ENDPOINT)
> +		bridge = dev;
> +	else
> +		bridge = pci_upstream_bridge(dev);
> +
> +	cxl_walk_bridge(bridge, cxl_report_error_detected, &status);
> +	if (status)
> +		panic("CXL cachemem error.");
> +
> +	if (host->native_aer || pcie_ports_native) {
> +		pcie_clear_device_status(dev);
> +		pci_aer_clear_nonfatal_status(dev);
> +	}
> +
> +	pci_info(bridge, "CXL uncorrectable error.\n");
> +}