PCI: disable Bus Master on PCI device shutdown

Disable Bus Master bit on the device in pci_device_shutdown() to ensure PCI
devices do not continue to DMA data after shutdown.  This can cause memory
corruption in case of a kexec where the current kernel shuts down and
transfers control to a new kernel while a PCI device continues to DMA to
memory that does not belong to it any more in the new kernel.

I have tested this code on two laptops, two workstations and a 16-socket
server.  kexec worked correctly on all of them.
Signed-off-by: Khalid Aziz <khalid.aziz@hp.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/pci-driver.c

@@ -420,6 +420,12 @@ static void pci_device_shutdown(struct device *dev)
 	pci_msi_shutdown(pci_dev);
 	pci_msix_shutdown(pci_dev);
 
+	/*
+	 * Turn off Bus Master bit on the device to tell it to not
+	 * continue to do DMA
+	 */
+	pci_disable_device(pci_dev);
+
 	/*
 	 * Devices may be enabled to wake up by runtime PM, but they need not
 	 * be supposed to wake up the system from its "power off" state (e.g.