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Message-ID: <ebfa2c44-7a12-4d73-81cb-5d74e99163d8@amd.com>
Date: Thu, 12 Jun 2025 11:29:22 -0500
From: "Bowman, Terry" <terry.bowman@....com>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc: PradeepVineshReddy.Kodamati@....com, dave@...olabs.net,
dave.jiang@...el.com, alison.schofield@...el.com, vishal.l.verma@...el.com,
ira.weiny@...el.com, dan.j.williams@...el.com, bhelgaas@...gle.com,
bp@...en8.de, ming.li@...omail.com, shiju.jose@...wei.com,
dan.carpenter@...aro.org, Smita.KoralahalliChannabasappa@....com,
kobayashi.da-06@...itsu.com, yanfei.xu@...el.com, rrichter@....com,
peterz@...radead.org, fabio.m.de.francesco@...ux.intel.com,
ilpo.jarvinen@...ux.intel.com, yazen.ghannam@....com,
linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-pci@...r.kernel.org
Subject: Re: [PATCH v9 05/16] CXL/PCI: Introduce CXL uncorrectable protocol
error recovery
On 6/12/2025 11:06 AM, Jonathan Cameron wrote:
> On Tue, 3 Jun 2025 12:22:28 -0500
> Terry Bowman <terry.bowman@....com> wrote:
>
>> Create cxl_do_recovery() to provide 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.
>>
>> Copy the PCI error driver's merge_result() and rename as cxl_merge_result().
>> Introduce PCI_ERS_RESULT_PANIC and add support in the cxl_merge_result()
>> routine.
> Do we need a separate version? PCI won't ever set PCI_ERS_RESULT_PANIC
> so new != PCI_ERS_RESULT_PANIC and the first condition would only do
> something on CXL.
Correct. A common merge_result() can be used. I'll change it.
- Terry
>> Copy pci_walk_bridge() to cxl_walk_bridge(). Make a change to walk the
>> first device in all cases.
>>
>> Copy the PCI error driver's report_error_detected() to cxl_report_error_detected().
>> Note, only CXL Endpoints are currently supported. Add locking for PCI
>> device as done in PCI's report_error_detected(). Add reference counting for
>> the CXL device responsible for cleanup of the CXL RAS. This is necessary
>> to prevent the RAS registers from disappearing before logging is completed.
>>
>> Call panic() to halt the system in the case of uncorrectable errors (UCE)
>> in cxl_do_recovery(). Export pci_aer_clear_fatal_status() for CXL to use
>> if a UCE is not found. In this case the AER status must be cleared and
>> uses pci_aer_clear_fatal_status().
>>
>> Signed-off-by: Terry Bowman <terry.bowman@....com>
>> ---
>> drivers/cxl/core/ras.c | 79 ++++++++++++++++++++++++++++++++++++++++++
>> include/linux/pci.h | 3 ++
>> 2 files changed, 82 insertions(+)
>>
>> diff --git a/drivers/cxl/core/ras.c b/drivers/cxl/core/ras.c
>> index 9ed5c682e128..715f7221ea3a 100644
>> --- a/drivers/cxl/core/ras.c
>> +++ b/drivers/cxl/core/ras.c
>> @@ -110,8 +110,87 @@ static DECLARE_WORK(cxl_cper_prot_err_work, cxl_cper_prot_err_work_fn);
>>
>> #ifdef CONFIG_PCIEAER_CXL
>>
>> +static pci_ers_result_t cxl_merge_result(enum pci_ers_result orig,
>> + enum pci_ers_result new)
>> +{
>> + if (new == PCI_ERS_RESULT_PANIC)
>> + return PCI_ERS_RESULT_PANIC;
>> +
>> + if (new == PCI_ERS_RESULT_NO_AER_DRIVER)
>> + return PCI_ERS_RESULT_NO_AER_DRIVER;
>> +
>> + if (new == PCI_ERS_RESULT_NONE)
>> + return orig;
>> +
>> + switch (orig) {
>> + case PCI_ERS_RESULT_CAN_RECOVER:
>> + case PCI_ERS_RESULT_RECOVERED:
>> + orig = new;
>> + break;
>> + case PCI_ERS_RESULT_DISCONNECT:
>> + if (new == PCI_ERS_RESULT_NEED_RESET)
>> + orig = PCI_ERS_RESULT_NEED_RESET;
>> + break;
>> + default:
>> + break;
>> + }
>> +
>> + return orig;
>> +}
>> +
>> +static int cxl_report_error_detected(struct pci_dev *pdev, void *data)
>> +{
>> + pci_ers_result_t vote, *result = data;
>> + struct cxl_dev_state *cxlds;
>> +
>> + if ((pci_pcie_type(pdev) != PCI_EXP_TYPE_ENDPOINT) &&
>> + (pci_pcie_type(pdev) != PCI_EXP_TYPE_RC_END))
>> + return 0;
>> +
>> + cxlds = pci_get_drvdata(pdev);
>> + struct device *dev __free(put_device) = get_device(&cxlds->cxlmd->dev);
>> +
>> + device_lock(&pdev->dev);
>> + vote = cxl_error_detected(pdev, pci_channel_io_frozen);
>> + *result = cxl_merge_result(*result, vote);
>> + device_unlock(&pdev->dev);
>> +
>> + return 0;
>> +}
>> +
>> +static void cxl_walk_bridge(struct pci_dev *bridge,
>> + int (*cb)(struct pci_dev *, void *),
>> + void *userdata)
>> +{
>> + if (cb(bridge, userdata))
>> + return;
>> +
>> + if (bridge->subordinate)
>> + pci_walk_bus(bridge->subordinate, cb, userdata);
>> +}
>> +
>> static void cxl_do_recovery(struct pci_dev *pdev)
>> {
>> + struct pci_host_bridge *host = pci_find_host_bridge(pdev->bus);
>> + pci_ers_result_t status = PCI_ERS_RESULT_CAN_RECOVER;
>> +
>> + cxl_walk_bridge(pdev, 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 (host->native_aer) {
>> + pcie_clear_device_status(pdev);
>> + pci_aer_clear_nonfatal_status(pdev);
>> + pci_aer_clear_fatal_status(pdev);
>> + }
>> +
>> + pci_info(pdev, "CXL uncorrectable error.\n");
>> }
>>
>> static int cxl_rch_handle_error_iter(struct pci_dev *pdev, void *data)
>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>> index cd53715d53f3..b0e7545162de 100644
>> --- a/include/linux/pci.h
>> +++ b/include/linux/pci.h
>> @@ -870,6 +870,9 @@ enum pci_ers_result {
>>
>> /* No AER capabilities registered for the driver */
>> PCI_ERS_RESULT_NO_AER_DRIVER = (__force pci_ers_result_t) 6,
>> +
>> + /* System is unstable, panic */
>> + PCI_ERS_RESULT_PANIC = (__force pci_ers_result_t) 7,
>> };
>>
>> /* PCI bus error event callbacks */
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