PCI: Fix Resizable BAR restore order

The commit 337b1b566db0 ("PCI: Fix restoring BARs on BAR resize rollback
path") changed BAR resize to layer rebar code and resource setup/restore
code cleanly. Unfortunately, it did not consider how the value of the BAR
Size field impacts the read-only bits in the Base Address Register (PCIe7
spec, sec. 7.8.6.3). That is, it very much matters in which order the BAR
Size and Base Address Register are restored.

Post-337b1b566db0 ("PCI: Fix restoring BARs on BAR resize rollback path")
during BAR resize rollback, pci_do_resource_release_and_resize() attempts
to restore the old address to the BAR that was resized, but it can fail to
setup the address correctly if the address has low bits set that collide
with the bits that are still read-only. As a result, kernel's resource and
BAR will be out-of-sync.

Fix this by restoring BAR Size before rolling back the resource changes and
restoring the BAR.

Fixes: 337b1b566db0 ("PCI: Fix restoring BARs on BAR resize rollback path")
Reported-by: Ville Syrjälä <[e-mail]>
Link: https://lore.kernel.org/linux-pci/[e-mail]/
Signed-off-by: Ilpo Järvinen <[e-mail]>
Signed-off-by: Bjorn Helgaas <[e-mail]>
Tested-by: Ville Syrjälä <[e-mail]>
Reviewed-by: Ville Syrjälä <[e-mail]>
Cc: [e-mail]
Link: https://patch.msgid.link/[e-mail]

drivers/pci/rebar.c

···
 			int exclude_bars)
 {
 	struct pci_host_bridge *host;
-	int old, ret;
 
 	/* Check if we must preserve the firmware's resource assignment */
 	host = pci_find_host_bridge(dev->bus);
···
 	if (!pci_rebar_size_supported(dev, resno, size))
 		return -EINVAL;
 
-	old = pci_rebar_get_current_size(dev, resno);
-	if (old < 0)
-		return old;
-
-	ret = pci_rebar_set_size(dev, resno, size);
-	if (ret)
-		return ret;
-
-	ret = pci_do_resource_release_and_resize(dev, resno, size, exclude_bars);
-	if (ret)
-		goto error_resize;
-	return 0;
-
-error_resize:
-	pci_rebar_set_size(dev, resno, old);
-	return ret;
+	return pci_do_resource_release_and_resize(dev, resno, size, exclude_bars);
 }
 EXPORT_SYMBOL(pci_resize_resource);

drivers/pci/setup-bus.c

···
 	struct resource *b_win, *r;
 	LIST_HEAD(saved);
 	unsigned int i;
-	int ret = 0;
+	int old, ret;
 
 	b_win = pbus_select_window(bus, res);
 	if (!b_win)
 		return -EINVAL;
+
+	old = pci_rebar_get_current_size(pdev, resno);
+	if (old < 0)
+		return old;
+
+	ret = pci_rebar_set_size(pdev, resno, size);
+	if (ret)
+		return ret;
 
 	pci_dev_for_each_resource(pdev, r, i) {
 		if (i >= PCI_BRIDGE_RESOURCES)
···
 	return ret;
 
 restore:
-	/* Revert to the old configuration */
+	/*
+	 * Revert to the old configuration.
+	 *
+	 * BAR Size must be restored first because it affects the read-only
+	 * bits in BAR (the old address might not be restorable otherwise
+	 * due to low address bits).
+	 */
+	pci_rebar_set_size(pdev, resno, old);
+
 	list_for_each_entry(dev_res, &saved, list) {
 		struct resource *res = dev_res->res;
 		struct pci_dev *dev = dev_res->dev;