1. Patchew
  2. linux
  3. [PATCH v7 0/9] Error recovery for vfio-pci devices on s390x
  4. View patch

[PATCH v7 3/9] PCI: Avoid saving config space state if inaccessible

Farhan Ali posted 9 patches 1 month ago
There is a newer version of this series
[PATCH v7 3/9] PCI: Avoid saving config space state if inaccessible
Posted by Farhan Ali 1 month ago 
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@linux.ibm.com>
---
 drivers/pci/pci.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index c105e285cff8..74d21c97654d 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;
 	const struct pci_error_handlers *err_handler =
 			dev->driver ? dev->driver->err_handler : NULL;
 
@@ -4980,6 +4981,12 @@ static void pci_dev_save_and_disable(struct pci_dev *dev)
 	 */
 	pci_set_power_state(dev, PCI_D0);
 
+	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
-- 
2.43.0
Re: [PATCH v7 3/9] PCI: Avoid saving config space state if inaccessible
Posted by Niklas Schnelle 2 weeks, 4 days ago 
On Wed, 2026-01-07 at 10:32 -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@linux.ibm.com>
> ---

Running checkpatch.pl with "--strict" on the series it pointed out that
this commit description has lines over 75 characters.

Thanks,
Niklas
Re: [PATCH v7 3/9] PCI: Avoid saving config space state if inaccessible
Posted by Niklas Schnelle 2 weeks, 5 days ago 
On Wed, 2026-01-07 at 10:32 -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@linux.ibm.com>
> ---
>  drivers/pci/pci.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index c105e285cff8..74d21c97654d 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;
>  	const struct pci_error_handlers *err_handler =
>  			dev->driver ? dev->driver->err_handler : NULL;
>  
> @@ -4980,6 +4981,12 @@ static void pci_dev_save_and_disable(struct pci_dev *dev)
>  	 */
>  	pci_set_power_state(dev, PCI_D0);
>  
> +	pci_read_config_dword(dev, PCI_COMMAND, &val);

Since the PCI_COMMAND field is only 16 bits I think it warrants a
comment that you're reading both PCI_COMMAND and PCI_STATUS and that
both together should never be 0xffffffff and why. I think at least
PCI_STATUS_PARITY should never be set in a config space we want to
restore.

> +	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

Functionally this looks good to me and I agree that with both DPC and
s390x PCI error state behavior this makes sense.

Thanks,
Niklas
Re: [PATCH v7 3/9] PCI: Avoid saving config space state if inaccessible
Posted by Farhan Ali 2 weeks, 4 days ago 
On 1/19/2026 1:23 PM, Niklas Schnelle wrote:
> On Wed, 2026-01-07 at 10:32 -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@linux.ibm.com>
>> ---
>>   drivers/pci/pci.c | 7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>> index c105e285cff8..74d21c97654d 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;
>>   	const struct pci_error_handlers *err_handler =
>>   			dev->driver ? dev->driver->err_handler : NULL;
>>   
>> @@ -4980,6 +4981,12 @@ static void pci_dev_save_and_disable(struct pci_dev *dev)
>>   	 */
>>   	pci_set_power_state(dev, PCI_D0);
>>   
>> +	pci_read_config_dword(dev, PCI_COMMAND, &val);
> Since the PCI_COMMAND field is only 16 bits I think it warrants a
> comment that you're reading both PCI_COMMAND and PCI_STATUS and that
> both together should never be 0xffffffff and why. I think at least
> PCI_STATUS_PARITY should never be set in a config space we want to
> restore.

Makes sense will add a comment. Note this is the mechanism used to check 
device config accessibility in pci_dev_wait() (for some context 
discussed here 
https://lore.kernel.org/all/cd1fa387-df80-4756-a2dc-5acdd0f09697@linux.ibm.com/). 


Thanks

Farhan

Patchew 2.1-devel-b67e4c2

© 2016 - 2026 Red Hat, Inc.