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

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Message-ID: <20260122194437.1903-4-alifm@linux.ibm.com>
Date: Thu, 22 Jan 2026 11:44:31 -0800
From: Farhan Ali <alifm@...ux.ibm.com>
To: 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, alifm@...ux.ibm.com, schnelle@...ux.ibm.com,
        mjrosato@...ux.ibm.com, julianr@...ux.ibm.com
Subject: [PATCH v8 3/9] PCI: Avoid saving config space state if inaccessible

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;
 	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
-- 
2.43.0