PCI: Don't update VF BARs while VF memory space is enabled

If we update a VF BAR while it's enabled, there are two potential problems:

  1) Any driver that's using the VF has a cached BAR value that is stale
     after the update, and

  2) We can't update 64-bit BARs atomically, so the intermediate state
     (new lower dword with old upper dword) may conflict with another
     device, and an access by a driver unrelated to the VF may cause a bus
     error.

Warn about attempts to update VF BARs while they are enabled.  This is a
programming error, so use dev_WARN() to get a backtrace.
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Gavin Shan <gwshan@linux.vnet.ibm.com>

drivers/pci/iov.c

@@ -584,6 +584,7 @@ void pci_iov_update_resource(struct pci_dev *dev, int resno)
 	struct resource *res = dev->resource + resno;
 	int vf_bar = resno - PCI_IOV_RESOURCES;
 	struct pci_bus_region region;
+	u16 cmd;
 	u32 new;
 	int reg;
 
@@ -595,6 +596,13 @@ void pci_iov_update_resource(struct pci_dev *dev, int resno)
 	if (!iov)
 		return;
 
+	pci_read_config_word(dev, iov->pos + PCI_SRIOV_CTRL, &cmd);
+	if ((cmd & PCI_SRIOV_CTRL_VFE) && (cmd & PCI_SRIOV_CTRL_MSE)) {
+		dev_WARN(&dev->dev, "can't update enabled VF BAR%d %pR\n",
+			 vf_bar, res);
+		return;
+	}
+
 	/*
 	 * Ignore unimplemented BARs, unused resource slots for 64-bit
 	 * BARs, and non-movable resources, e.g., those described via