iommu/vt-d: dmar_parse_one_rmrr: replace WARN_TAINT with pr_warn + add_taint

Quoting from the comment describing the WARN functions in
include/asm-generic/bug.h:

 * WARN(), WARN_ON(), WARN_ON_ONCE, and so on can be used to report
 * significant kernel issues that need prompt attention if they should ever
 * appear at runtime.
 *
 * Do not use these macros when checking for invalid external inputs

The (buggy) firmware tables which the dmar code was calling WARN_TAINT
for really are invalid external inputs. They are not under the kernel's
control and the issues in them cannot be fixed by a kernel update.
So logging a backtrace, which invites bug reports to be filed about this,
is not helpful.

Some distros, e.g. Fedora, have tools watching for the kernel backtraces
logged by the WARN macros and offer the user an option to file a bug for
this when these are encountered. The WARN_TAINT in dmar_parse_one_rmrr
+ another iommu WARN_TAINT, addressed in another patch, have lead to over
a 100 bugs being filed this way.

This commit replaces the WARN_TAINT("...") call, with a
pr_warn(FW_BUG "...") + add_taint(TAINT_FIRMWARE_WORKAROUND, ...) call
avoiding the backtrace and thus also avoiding bug-reports being filed
about this against the kernel.

Fixes: f5a68bb075 ("iommu/vt-d: Mark firmware tainted if RMRR fails sanity check")
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Acked-by: Lu Baolu <baolu.lu@linux.intel.com>
Cc: stable@vger.kernel.org
Cc: Barret Rhoden <brho@google.com>
Link: https://lore.kernel.org/r/20200309140138.3753-3-hdegoede@redhat.com
BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1808874

drivers/iommu/intel-iommu.c

@@ -4460,14 +4460,16 @@ int __init dmar_parse_one_rmrr(struct acpi_dmar_header *header, void *arg)
 	struct dmar_rmrr_unit *rmrru;
 
 	rmrr = (struct acpi_dmar_reserved_memory *)header;
-	if (rmrr_sanity_check(rmrr))
-		WARN_TAINT(1, TAINT_FIRMWARE_WORKAROUND,
+	if (rmrr_sanity_check(rmrr)) {
+		pr_warn(FW_BUG
 			   "Your BIOS is broken; bad RMRR [%#018Lx-%#018Lx]\n"
 			   "BIOS vendor: %s; Ver: %s; Product Version: %s\n",
 			   rmrr->base_address, rmrr->end_address,
 			   dmi_get_system_info(DMI_BIOS_VENDOR),
 			   dmi_get_system_info(DMI_BIOS_VERSION),
 			   dmi_get_system_info(DMI_PRODUCT_VERSION));
+		add_taint(TAINT_FIRMWARE_WORKAROUND, LOCKDEP_STILL_OK);
+	}
 
 	rmrru = kzalloc(sizeof(*rmrru), GFP_KERNEL);
 	if (!rmrru)