[PATCH] PCI: decline to resize resources if boot config must be preserved

[Ard Biesheuvel]

The _DSM #5 method in the ACPI host bridge object tells us whether the
OS is permitted to deviate from the resource assignment configured by
the firmware. If this is not the case, we should not permit drivers to
resize BARs on the fly. So make pci_resize_resource() take this into
account.

Cc: <stable@xxxxxxxxxxxxxxx> # v5.4+
Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
---
 drivers/pci/setup-res.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-res.c
index 43eda101fcf4..3b38be081e93 100644
--- a/drivers/pci/setup-res.c
+++ b/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;
-- 
2.17.1