linux-kernel - Re: [PATCH v10 07/17] CXL/PCI: Introduce CXL uncorrectable protocol error recovery

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Message-ID: <8768d54b-80fd-46a9-b760-a84af06ca29d@amd.com>
Date: Wed, 2 Jul 2025 16:34:16 -0500
From: "Bowman, Terry" <terry.bowman@....com>
To: Shiju Jose <shiju.jose@...wei.com>, "dave@...olabs.net"
 <dave@...olabs.net>, Jonathan Cameron <jonathan.cameron@...wei.com>,
 "dave.jiang@...el.com" <dave.jiang@...el.com>,
 "alison.schofield@...el.com" <alison.schofield@...el.com>,
 "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
 "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
 "ming.li@...omail.com" <ming.li@...omail.com>,
 "Smita.KoralahalliChannabasappa@....com"
 <Smita.KoralahalliChannabasappa@....com>, "rrichter@....com"
 <rrichter@....com>, "dan.carpenter@...aro.org" <dan.carpenter@...aro.org>,
 "PradeepVineshReddy.Kodamati@....com" <PradeepVineshReddy.Kodamati@....com>,
 "lukas@...ner.de" <lukas@...ner.de>,
 "Benjamin.Cheatham@....com" <Benjamin.Cheatham@....com>,
 "sathyanarayanan.kuppuswamy@...ux.intel.com"
 <sathyanarayanan.kuppuswamy@...ux.intel.com>,
 "linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [PATCH v10 07/17] CXL/PCI: Introduce CXL uncorrectable protocol
 error recovery



On 6/27/2025 7:27 AM, Shiju Jose wrote:
>> -----Original Message-----
>> From: Terry Bowman <terry.bowman@....com>
>> Sent: 26 June 2025 23:43
>> To: dave@...olabs.net; Jonathan Cameron <jonathan.cameron@...wei.com>;
>> dave.jiang@...el.com; alison.schofield@...el.com; dan.j.williams@...el.com;
>> bhelgaas@...gle.com; Shiju Jose <shiju.jose@...wei.com>;
>> ming.li@...omail.com; Smita.KoralahalliChannabasappa@....com;
>> rrichter@....com; dan.carpenter@...aro.org;
>> PradeepVineshReddy.Kodamati@....com; lukas@...ner.de;
>> Benjamin.Cheatham@....com;
>> sathyanarayanan.kuppuswamy@...ux.intel.com; terry.bowman@....com;
>> linux-cxl@...r.kernel.org
>> Cc: linux-kernel@...r.kernel.org; linux-pci@...r.kernel.org
>> Subject: [PATCH v10 07/17] CXL/PCI: Introduce CXL uncorrectable protocol error
>> recovery
>>
>> 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.
>>
>> Export the PCI error driver's merge_result() to CXL namespace. Introduce
>> PCI_ERS_RESULT_PANIC and add support in merge_result() routine. This will be
>> used by CXL to panic the system in the case of uncorrectable protocol errors. PCI
>> error handling is not currently expected to use the PCI_ERS_RESULT_PANIC.
>>
>> 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 and RCH Downstream Ports(RCH DSP) are currently
>> supported. Add locking for PCI device as done in PCI's report_error_detected().
>> 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/native_ras.c | 44 +++++++++++++++++++++++++++++++++++
>> drivers/pci/pcie/cxl_aer.c    |  3 ++-
>> drivers/pci/pcie/err.c        |  8 +++++--
>> include/linux/aer.h           | 11 +++++++++
>> include/linux/pci.h           |  3 +++
>> 5 files changed, 66 insertions(+), 3 deletions(-)
>>
> [...]
>> void pci_print_aer(struct pci_dev *dev, int aer_severity, diff --git
>> a/include/linux/pci.h b/include/linux/pci.h index 79326358f641..16a8310e0373
>> 100644
>> --- a/include/linux/pci.h
>> +++ b/include/linux/pci.h
>> @@ -868,6 +868,9 @@ 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. Is CXL specific  */
>> +	PCI_ERS_RESULT_PANIC = (__force pci_ers_result_t) 7,
> Extra space is present after casting?
>> };

Hi Shiju,

I see the existing PCIE_ERS_RESULT entries have a space before the number.
For example,

PCI_ERS_RESULT_NO_AER_DRIVER = (__force pci_ers_result_t) 6,
                                                         ^

I do see that I had an extra space in my comment that I will fix.
Please let me know if you agree or if I'm missing something?

-Terry
>>
>> /* PCI bus error event callbacks */
>> --
>> 2.34.1