Re: [PATCH v2 1/6] PCI/DPC: Avoid access to non-existent AER capability

[Yazen Ghannam]

On Tue, Oct 20, 2026 at 11:19:18AM -0700, Kuppuswamy Sathyanarayanan wrote:
> From: Lukas Wunner <lukas@xxxxxxxxx>
> 
> Downstream Port Containment does not mandate presence of an Advanced Error
> Reporting capability, so a Downstream Port may support DPC, but not AER
> (PCIe r7.1 sec 6.2.11.2).
> 
> In February 2019, commit 9f08a5d896ce ("PCI/DPC: Fix print AER status in
> DPC event handling") amended the DPC driver to access the AER capability
> without checking for its presence.
> 
> In May 2020, commit 708b20003624 ("PCI/AER: Remove HEST/FIRMWARE_FIRST
> parsing for AER ownership") fixed it by inserting a call to
> pcie_aer_is_native() in dpc_probe(), which implicitly checks for presence
> of an AER capability.
> 
> However already in October 2019, commit 35a0b2378c19 ("PCI/DPC: Add
> "pcie_ports=dpc-native" to allow DPC without AER control") made it
> possible to override the check:  The DPC driver may access a non-existent
> AER capability if "pcie_ports=dpc-native" is passed on the command line.
> 
> Fix it by making the DPC driver cope with AER-unsupporting Downstream
> Ports.
> 
> There are two places where the AER capability is accessed:
> 
> - dpc_get_aer_uncorrect_severity() uses it to discern whether a Fatal or
>   Non-Fatal Error triggered DPC.  Access the Device Status Register
>   instead, in accordance with PCIe r7.1 sec 6.2.5.
> 
> - dpc_is_surprise_removal() uses it to detect whether a Surprise Down
>   Error triggered DPC.  Return false on AER-unsupporting devices.  The
>   function works around an AMD-specific quirk and it seems reasonable to
>   assume that all affected products are AER-supporting.  In any case the
>   detection is not possible without AER capability.
> 
> Insert a temporary check for an AER capability after the call to
> aer_get_device_error_info() because the function currently returns false
> for AER-unsupporting devices.  The check will become obsolete and will be
> removed with the imminent baseline capability error reporting.
> 
> Fixes: 35a0b2378c19 ("PCI/DPC: Add "pcie_ports=dpc-native" to allow DPC without AER control")
> Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # v5.5+
> ---
>  drivers/pci/pcie/dpc.c | 23 ++++++++++-------------
>  1 file changed, 10 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/pci/pcie/dpc.c b/drivers/pci/pcie/dpc.c
> index 2b779bd1d861..793a799053f1 100644
> --- a/drivers/pci/pcie/dpc.c
> +++ b/drivers/pci/pcie/dpc.c
> @@ -236,21 +236,15 @@ static void dpc_process_rp_pio_error(struct pci_dev *pdev)
>  static int dpc_get_aer_uncorrect_severity(struct pci_dev *dev,
>  					  struct aer_err_info *info)
>  {
> -	int pos = dev->aer_cap;
> -	u32 status, mask, sev;
> +	u16 devsta;
>  
> -	pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_STATUS, &status);
> -	pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_MASK, &mask);
> -	status &= ~mask;
> -	if (!status)
> -		return 0;
> -
> -	pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_SEVER, &sev);
> -	status &= sev;
> -	if (status)
> +	pcie_capability_read_word(dev, PCI_EXP_DEVSTA, &devsta);
> +	if (devsta & PCI_EXP_DEVSTA_FED)
>  		info->severity = AER_FATAL;
> -	else
> +	else if (devsta & PCI_EXP_DEVSTA_NFED)
>  		info->severity = AER_NONFATAL;
> +	else
> +		return 0;
>  
>  	info->level = KERN_ERR;

Did you settle your question from here?

https://lore.kernel.org/all/74fe0d79-dc90-4c05-ba9c-9a0eec1ada48@xxxxxxxxxxxxxxx/

Thanks,
Yazen