linux-kernel - Re: [PATCH v8 3/9] PCI: Avoid saving config space state if inaccessible

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Message-ID: <344d4e1c57d2eeb750b0c0edf12d88eb31e05ed0.camel@linux.ibm.com>
Date: Mon, 26 Jan 2026 22:00:10 +0100
From: Niklas Schnelle <schnelle@...ux.ibm.com>
To: Farhan Ali <alifm@...ux.ibm.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Cc: helgaas@...nel.org, lukas@...ner.de, alex@...zbot.org, clg@...hat.com,
        stable@...r.kernel.org, mjrosato@...ux.ibm.com, julianr@...ux.ibm.com
Subject: Re: [PATCH v8 3/9] PCI: Avoid saving config space state if
 inaccessible

On Thu, 2026-01-22 at 11:44 -0800, Farhan Ali wrote:
> The current reset process saves the device's config space state before
> reset and restores it afterward. However errors may occur unexpectedly and
> it may then be impossible to save config space because the device may be
> inaccessible (e.g. DPC) or config space may be corrupted. This results in
> saving corrupted values that get written back to the device during state
> restoration.
> 
> With a reset we want to recover/restore the device into a functional state.
> So avoid saving the state of the config space when the device config space
> is inaccessible.
> 
> Signed-off-by: Farhan Ali <alifm@...ux.ibm.com>
> ---
>  drivers/pci/pci.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index c105e285cff8..e7beaf1f65a7 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4960,6 +4960,7 @@ EXPORT_SYMBOL_GPL(pci_dev_unlock);
>  
>  static void pci_dev_save_and_disable(struct pci_dev *dev)
>  {
> +	u32 val;

Nit: I believe the PCI subsystem prefers reverse X-mas tree
declarations

>  	const struct pci_error_handlers *err_handler =
>  			dev->driver ? dev->driver->err_handler : NULL;
>  
> @@ -4980,6 +4981,19 @@ static void pci_dev_save_and_disable(struct pci_dev *dev)
>  	 */
>  	pci_set_power_state(dev, PCI_D0);
>  
> +	/*
> +	 * If device's config space is inaccessible it can return ~0 for
> +	 * any reads. Since VFs can also return ~0 for Device and Vendor ID
> +	 * check Command and Status registers. At the very least we should
> +	 * avoid restoring config space for device with error bits set in
> +	 * Status register.
> +	 */
> +	pci_read_config_dword(dev, PCI_COMMAND, &val);
> +	if (PCI_POSSIBLE_ERROR(val)) {
> +		pci_warn(dev, "Device config space inaccessible\n");
> +		return;
> +	}
> +
>  	pci_save_state(dev);
>  	/*
>  	 * Disable the device by clearing the Command register, except for

Looks good to me thanks! Feel free to add:

Reviewed-by: Niklas Schnelle <schnelle@...ux.ibm.com>