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

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Message-ID: <20250627120541.00003a14@huawei.com>
Date: Fri, 27 Jun 2025 12:05:41 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Terry Bowman <terry.bowman@....com>
CC: <dave@...olabs.net>, <dave.jiang@...el.com>, <alison.schofield@...el.com>,
	<dan.j.williams@...el.com>, <bhelgaas@...gle.com>, <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>,
	<linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-pci@...r.kernel.org>
Subject: Re: [PATCH v10 07/17] CXL/PCI: Introduce CXL uncorrectable protocol
 error recovery

On Thu, 26 Jun 2025 17:42:42 -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.
> 
> Export the PCI error driver's merge_result() to CXL namespace.

I think this may be a confusion from earlier review.  Anyhow, it should
be namespaced in the sense of not exporting something the vague name of
merge_result but it's PCI code, not CXL code and we don't have the dangerous
interface argument to justify putting it in the CXL namespace so I think
a namespaced EXPORT makes little sense for this one.

Jonathan


> 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>


> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
> index de6381c690f5..63fceb3e8613 100644
> --- a/drivers/pci/pcie/err.c
> +++ b/drivers/pci/pcie/err.c
> @@ -21,9 +21,12 @@
>  #include "portdrv.h"
>  #include "../pci.h"
>  
> -static pci_ers_result_t merge_result(enum pci_ers_result orig,
> -				  enum pci_ers_result new)
> +pci_ers_result_t 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;
>  
> @@ -45,6 +48,7 @@ static pci_ers_result_t merge_result(enum pci_ers_result orig,
>  
>  	return orig;
>  }
> +EXPORT_SYMBOL_NS_GPL(merge_result, "CXL"); 

Do we care about namespacing this?  I think not given it is PCIe code
and hardly destructive for other drivers to mess with it if they like.

I would namespace it in the sense of renaming it to make it clear
it's about pci errors though.

pci_ers_merge_result() perhaps?

Do that as a percursor patch.


>  
>  static int report_error_detected(struct pci_dev *dev,
>  				 pci_channel_state_t state,