linux-kernel - Re: [PATCH v3 05/15] PCI/AER: Add CXL PCIe port correctable error support in AER service driver

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Message-ID: <20241127170327.00000374@huawei.com>
Date: Wed, 27 Nov 2024 17:03:27 +0000
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Terry Bowman <terry.bowman@....com>
CC: <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-pci@...r.kernel.org>, <nifan.cxl@...il.com>, <ming4.li@...el.com>,
	<dave@...olabs.net>, <dave.jiang@...el.com>, <alison.schofield@...el.com>,
	<vishal.l.verma@...el.com>, <dan.j.williams@...el.com>,
	<bhelgaas@...gle.com>, <mahesh@...ux.ibm.com>, <ira.weiny@...el.com>,
	<oohall@...il.com>, <Benjamin.Cheatham@....com>, <rrichter@....com>,
	<nathan.fontenot@....com>, <Smita.KoralahalliChannabasappa@....com>,
	<lukas@...ner.de>
Subject: Re: [PATCH v3 05/15] PCI/AER: Add CXL PCIe port correctable error
 support in AER service driver

On Wed, 13 Nov 2024 15:54:19 -0600
Terry Bowman <terry.bowman@....com> wrote:

> The AER service driver supports handling downstream port protocol errors in
> restricted CXL host (RCH) mode also known as CXL1.1. It needs the same
> functionality for CXL PCIe ports operating in virtual hierarchy (VH)
> mode.[1]
> 
> CXL and PCIe protocol error handling have different requirements that
> necessitate a separate handling path. The AER service driver may try to
> recover PCIe uncorrectable non-fatal errors (UCE). The same recovery is not
> suitable for CXL PCIe port devices because of potential for system memory
> corruption. Instead, CXL protocol error handling must use a kernel panic
> in the case of a fatal or non-fatal UCE. The AER driver's PCIe error
> handling does not panic the kernel in response to a UCE.
> 
> Introduce a separate path for CXL protocol error handling in the AER
> service driver. This will allow CXL protocol errors to use CXL specific
> handling instead of PCIe handling. Add the CXL specific changes without
> affecting or adding functionality in the PCIe handling.
> 
> Make this update alongside the existing downstream port RCH error handling
> logic, extending support to CXL PCIe ports in VH mode.
> 
> is_internal_error() is currently limited by CONFIG_PCIEAER_CXL kernel
> config. Update is_internal_error()'s function declaration such that it is
> always available regardless if CONFIG_PCIEAER_CXL kernel config is enabled
> or disabled.
> 
> The uncorrectable error (UCE) handling will be added in a future patch.
> 
> [1] CXL 3.1 Spec, 12.2.2 CXL Root Ports, Downstream Switch Ports, and
> Upstream Switch Ports
> 
> Signed-off-by: Terry Bowman <terry.bowman@....com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Reviewed-by: Dave Jiang <dave.jiang@...el.com>
I took another look and so a question inline.

Jonathan

>  static int cxl_rch_handle_error_iter(struct pci_dev *dev, void *data)
>  {
>  	struct aer_err_info *info = (struct aer_err_info *)data;
> @@ -1033,14 +1032,23 @@ static int cxl_rch_handle_error_iter(struct pci_dev *dev, void *data)
>  
>  static void cxl_handle_error(struct pci_dev *dev, struct aer_err_info *info)
>  {
> -	/*
> -	 * Internal errors of an RCEC indicate an AER error in an
> -	 * RCH's downstream port. Check and handle them in the CXL.mem
> -	 * device driver.
> -	 */
> -	if (pci_pcie_type(dev) == PCI_EXP_TYPE_RC_EC &&
> -	    is_internal_error(info))
> +	if (pci_pcie_type(dev) == PCI_EXP_TYPE_RC_EC)
>  		pcie_walk_rcec(dev, cxl_rch_handle_error_iter, info);
> +
> +	if (info->severity == AER_CORRECTABLE) {
> +		struct pci_driver *pdrv = dev->driver;
> +		int aer = dev->aer_cap;
> +
> +		if (aer)

How do we get here with no aer?

On a PCIe device AER is optional, but not I think on a CXL device
(I can't find the text but there is a change log entry that says
to clarify that it is required for CXL devices)

Maybe the optionality is why the PCIe code has this check.

Anyhow, I don't really mind keeping it, was just curious.

> +			pci_write_config_dword(dev, aer + PCI_ERR_COR_STATUS,
> +					       info->status);
> +
> +		if (pdrv && pdrv->cxl_err_handler &&
> +		    pdrv->cxl_err_handler->cor_error_detected)
> +			pdrv->cxl_err_handler->cor_error_detected(dev);
> +
> +		pcie_clear_device_status(dev);
> +	}
>  }