Re: [PATCH v2 1/2] PCI/MSI: Skip MSI-X restoration when configuration is inaccessible

[Farhan Ali <alifm@linux.ibm.com>]

On 11/6/2026 3:18 AM, Richard Cheng wrote:
> PCI state restoration runs even when a reset fails. If the device's
> configuration space remains inaccessible, MSI-X restoration can issue
> table MMIO accesses that trigger additional errors, including DPC
> containment.
>
> Check the existing PCI Command register read and skip MSI-X restoration
> if it fails or returns all ones. Preserve the existing handling of a
> valid Command register with Memory Space Enable clear, which temporarily
> enables memory decoding while restoring the MSI-X table.
>
> Limit the change to MSI-X restoration. Leave other PCI state
> restoration, driver reset callbacks, and reset return values unchanged.
>
> Signed-off-by: Richard Cheng <icheng@nvidia.com>

Just curious, why are we limiting this to only MSI-X and not MSI? I 
think MSI restoration will fail as well since the config space is not 
accessible.

> ---
>   drivers/pci/msi/msi.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/msi/msi.c b/drivers/pci/msi/msi.c
> index 8a0133a6a286..37de31f4cfb6 100644
> --- a/drivers/pci/msi/msi.c
> +++ b/drivers/pci/msi/msi.c
> @@ -887,7 +887,11 @@ void __pci_restore_msix_state(struct pci_dev *dev)
>   	 * Since the MSI-X Table and PBA are in Memory Space, enable it
>   	 * while restoring them.
>   	 */
> -	pci_read_config_word(dev, PCI_COMMAND, &cmd);
> +	if (pci_read_config_word(dev, PCI_COMMAND, &cmd) ||
> +	    PCI_POSSIBLE_ERROR(cmd)) {
> +		pci_warn(dev, "Device config space inaccessible; unable to restore MSI-X state\n");
> +		return;
> +	}

We have a helper function pci_dev_config_accessible() that does the same 
check, so might be appropriate to use (of course we would have to make 
the function global rather than static).

And maybe the check should be moved up before any config space access in 
this function?

Thanks

Farhan


>   	pci_write_config_word(dev, PCI_COMMAND, cmd | PCI_COMMAND_MEMORY);
>   
>   	write_msg = arch_restore_msi_irqs(dev);