[PATCH] Revert "PCI: Avoid reset when disabled via sysfs"

[PATCH] Revert "PCI: Avoid reset when disabled via sysfs"

[Alex Williamson]

This reverts commit 479380efe1625e251008d24b2810283db60d6fcd.

The reset_method attribute on a PCI device is only intended to manage
the availability of function scoped resets for a device.  It was never
intended to restrict resets targeting the bus or slot.

In introducing a restriction that each device must support function
level reset by testing pci_reset_supported(), we essentially create a
catch-22, that a device must have a function scope reset in order to
support bus/slot reset, when we use bus/slot reset to effect a reset
of a device that does not support a function scoped reset, especially
multi-function devices.

This breaks the majority of uses cases where vfio-pci uses bus/slot
resets to manage multifunction devices that do not support function
scoped resets.

Fixes: 479380efe162 ("PCI: Avoid reset when disabled via sysfs")
Reported-by: Cal Peake <cp@absolutedigital.net>
Link: https://lore.kernel.org/all/808e1111-27b7-f35b-6d5c-5b275e73677b@absolutedigital.net
Cc: stable@vger.kernel.org
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
 drivers/pci/pci.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 4d7c9f64ea24..e77d5b53c0ce 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5429,8 +5429,6 @@ static bool pci_bus_resettable(struct pci_bus *bus)
 		return false;
 
 	list_for_each_entry(dev, &bus->devices, bus_list) {
-		if (!pci_reset_supported(dev))
-			return false;
 		if (dev->dev_flags & PCI_DEV_FLAGS_NO_BUS_RESET ||
 		    (dev->subordinate && !pci_bus_resettable(dev->subordinate)))
 			return false;
@@ -5507,8 +5505,6 @@ static bool pci_slot_resettable(struct pci_slot *slot)
 	list_for_each_entry(dev, &slot->bus->devices, bus_list) {
 		if (!dev->slot || dev->slot != slot)
 			continue;
-		if (!pci_reset_supported(dev))
-			return false;
 		if (dev->dev_flags & PCI_DEV_FLAGS_NO_BUS_RESET ||
 		    (dev->subordinate && !pci_bus_resettable(dev->subordinate)))
 			return false;
-- 
2.48.1

RE: [PATCH] Revert "PCI: Avoid reset when disabled via sysfs"

[Tian, Kevin]

> From: Alex Williamson <alex.williamson@redhat.com>
> Sent: Tuesday, April 15, 2025 5:18 AM
> 
> This reverts commit 479380efe1625e251008d24b2810283db60d6fcd.
> 
> The reset_method attribute on a PCI device is only intended to manage
> the availability of function scoped resets for a device.  It was never
> intended to restrict resets targeting the bus or slot.
> 
> In introducing a restriction that each device must support function
> level reset by testing pci_reset_supported(), we essentially create a
> catch-22, that a device must have a function scope reset in order to
> support bus/slot reset, when we use bus/slot reset to effect a reset
> of a device that does not support a function scoped reset, especially
> multi-function devices.
> 
> This breaks the majority of uses cases where vfio-pci uses bus/slot
> resets to manage multifunction devices that do not support function
> scoped resets.
> 
> Fixes: 479380efe162 ("PCI: Avoid reset when disabled via sysfs")
> Reported-by: Cal Peake <cp@absolutedigital.net>
> Link: https://lore.kernel.org/all/808e1111-27b7-f35b-6d5c-
> 5b275e73677b@absolutedigital.net
> Cc: stable@vger.kernel.org
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

Reviewed-by: Kevin Tian <kevin.tian@intel.com>

Re: [PATCH] Revert "PCI: Avoid reset when disabled via sysfs"

[Bjorn Helgaas]

On Mon, Apr 14, 2025 at 03:18:23PM -0600, Alex Williamson wrote:
> This reverts commit 479380efe1625e251008d24b2810283db60d6fcd.
> 
> The reset_method attribute on a PCI device is only intended to manage
> the availability of function scoped resets for a device.  It was never
> intended to restrict resets targeting the bus or slot.
> 
> In introducing a restriction that each device must support function
> level reset by testing pci_reset_supported(), we essentially create a
> catch-22, that a device must have a function scope reset in order to
> support bus/slot reset, when we use bus/slot reset to effect a reset
> of a device that does not support a function scoped reset, especially
> multi-function devices.
> 
> This breaks the majority of uses cases where vfio-pci uses bus/slot
> resets to manage multifunction devices that do not support function
> scoped resets.
> 
> Fixes: 479380efe162 ("PCI: Avoid reset when disabled via sysfs")
> Reported-by: Cal Peake <cp@absolutedigital.net>
> Link: https://lore.kernel.org/all/808e1111-27b7-f35b-6d5c-5b275e73677b@absolutedigital.net
> Cc: stable@vger.kernel.org
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

Applied with Kevin's reviewed-by to pci/for-linus for v6.15, thanks,
and sorry for the breakage.

> ---
>  drivers/pci/pci.c | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 4d7c9f64ea24..e77d5b53c0ce 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5429,8 +5429,6 @@ static bool pci_bus_resettable(struct pci_bus *bus)
>  		return false;
>  
>  	list_for_each_entry(dev, &bus->devices, bus_list) {
> -		if (!pci_reset_supported(dev))
> -			return false;
>  		if (dev->dev_flags & PCI_DEV_FLAGS_NO_BUS_RESET ||
>  		    (dev->subordinate && !pci_bus_resettable(dev->subordinate)))
>  			return false;
> @@ -5507,8 +5505,6 @@ static bool pci_slot_resettable(struct pci_slot *slot)
>  	list_for_each_entry(dev, &slot->bus->devices, bus_list) {
>  		if (!dev->slot || dev->slot != slot)
>  			continue;
> -		if (!pci_reset_supported(dev))
> -			return false;
>  		if (dev->dev_flags & PCI_DEV_FLAGS_NO_BUS_RESET ||
>  		    (dev->subordinate && !pci_bus_resettable(dev->subordinate)))
>  			return false;
> -- 
> 2.48.1
>