PCI: Decline to resize resources if boot config must be preserved

commit 729e3a6 upstream.

The _DSM #5 method in the ACPI host bridge object tells us whether the OS
must preserve the resource assignments done by firmware. If this is the
case, we should not permit drivers to resize BARs on the fly. Make
pci_resize_resource() take this into account.

Link: https://lore.kernel.org/r/20210109095353.13417-1-ardb@kernel.org
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable@vger.kernel.org	# v5.4+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/pci/setup-res.c

@@ -410,10 +410,16 @@ EXPORT_SYMBOL(pci_release_resource);
 int pci_resize_resource(struct pci_dev *dev, int resno, int size)
 {
 	struct resource *res = dev->resource + resno;
+	struct pci_host_bridge *host;
 	int old, ret;
 	u32 sizes;
 	u16 cmd;
 
+	/* Check if we must preserve the firmware's resource assignment */
+	host = pci_find_host_bridge(dev->bus);
+	if (host->preserve_config)
+		return -ENOTSUPP;
+
 	/* Make sure the resource isn't assigned before resizing it. */
 	if (!(res->flags & IORESOURCE_UNSET))
 		return -EBUSY;