[PATCH v11 3/9] PCI: Avoid saving config space state if inaccessible

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

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>
Reviewed-by: Niklas Schnelle <schnelle@linux.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 a93084053537..373421f4b9d8 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5014,6 +5014,7 @@ static void pci_dev_save_and_disable(struct pci_dev *dev)
 {
 	const struct pci_error_handlers *err_handler =
 			dev->driver ? dev->driver->err_handler : NULL;
+	u32 val;
 
 	/*
 	 * dev->driver->err_handler->reset_prepare() is protected against
@@ -5033,6 +5034,19 @@ 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
-- 
2.43.0