From 729e3a669d1b62e9876a671ac03ccba399a23b68 Mon Sep 17 00:00:00 2001
From: Ard Biesheuvel <ardb@kernel.org>
Date: Sat, 9 Jan 2021 10:53:53 +0100
Subject: [PATCH] PCI: Decline to resize resources if boot config must be preserved
Git-commit: 729e3a669d1b62e9876a671ac03ccba399a23b68
Patch-mainline: v5.12-rc1
References: git-fixes

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+
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 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..7f1acb3918d0 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;
-- 
2.26.2