intel-iommu: Check for an RMRR which ends before it starts.

Some HP BIOSes report an RMRR region (a region which needs a 1:1 mapping
in the IOMMU for a given device) which has an end address lower than its
start address. Detect that and warn, rather than triggering the
BUG() in dma_pte_clear_range().

Cc: stable@kernel.org
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/pci/intel-iommu.c

@@ -2000,6 +2000,16 @@ static int iommu_prepare_identity_map(struct pci_dev *pdev,
 	       "IOMMU: Setting identity map for device %s [0x%Lx - 0x%Lx]\n",
 	       pci_name(pdev), start, end);
 	
+	if (end < start) {
+		WARN(1, "Your BIOS is broken; RMRR ends before it starts!\n"
+			"BIOS vendor: %s; Ver: %s; Product Version: %s\n",
+			dmi_get_system_info(DMI_BIOS_VENDOR),
+			dmi_get_system_info(DMI_BIOS_VERSION),
+		     dmi_get_system_info(DMI_PRODUCT_VERSION));
+		ret = -EIO;
+		goto error;
+	}
+
 	if (end >> agaw_to_width(domain->agaw)) {
 		WARN(1, "Your BIOS is broken; RMRR exceeds permitted address width (%d bits)\n"
 		     "BIOS vendor: %s; Ver: %s; Product Version: %s\n",