intel-iommu: Detect DMAR in hyperspace at probe time.

Many BIOSes will lie to us about the existence of an IOMMU, and claim
that there is one at an address which actually returns all 0xFF.

We need to detect this early, so that we know we don't have a viable
IOMMU and can set up swiotlb before it's too late.

Cc: stable@kernel.org
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/pci/dmar.c

@@ -632,6 +632,9 @@ int __init check_zero_address(void)
 		}
 
 		if (entry_header->type == ACPI_DMAR_TYPE_HARDWARE_UNIT) {
+			void __iomem *addr;
+			u64 cap, ecap;
+
 			drhd = (void *)entry_header;
 			if (!drhd->address) {
 				/* Promote an attitude of violence to a BIOS engineer today */
@@ -640,17 +643,38 @@ int __init check_zero_address(void)
 				     dmi_get_system_info(DMI_BIOS_VENDOR),
 				     dmi_get_system_info(DMI_BIOS_VERSION),
 				     dmi_get_system_info(DMI_PRODUCT_VERSION));
-#ifdef CONFIG_DMAR
-				dmar_disabled = 1;
-#endif
-				return 0;
+				goto failed;
+			}
+
+			addr = early_ioremap(drhd->address, VTD_PAGE_SIZE);
+			if (!addr ) {
+				printk("IOMMU: can't validate: %llx\n", drhd->address);
+				goto failed;
+			}
+			cap = dmar_readq(addr + DMAR_CAP_REG);
+			ecap = dmar_readq(addr + DMAR_ECAP_REG);
+			early_iounmap(addr, VTD_PAGE_SIZE);
+			if (cap == (uint64_t)-1 && ecap == (uint64_t)-1) {
+				/* Promote an attitude of violence to a BIOS engineer today */
+				WARN(1, "Your BIOS is broken; DMAR reported at address %llx returns all ones!\n"
+				     "BIOS vendor: %s; Ver: %s; Product Version: %s\n",
+				      drhd->address,
+				      dmi_get_system_info(DMI_BIOS_VENDOR),
+				      dmi_get_system_info(DMI_BIOS_VERSION),
+				      dmi_get_system_info(DMI_PRODUCT_VERSION));
+				goto failed;
 			}
-			break;
 		}
 
 		entry_header = ((void *)entry_header + entry_header->length);
 	}
 	return 1;
+
+failed:
+#ifdef CONFIG_DMAR
+	dmar_disabled = 1;
+#endif
+	return 0;
 }
 
 void __init detect_intel_iommu(void)