nfit/ars: Avoid stale ARS results

Gate ARS result consumption on whether the OS issued start-ARS since the
previous consumption. The BIOS may only clear its result buffers after a
successful start-ARS.

Fixes: 0caeef63e6 ("libnvdimm: Add a poison list and export badblocks")
Cc: <stable@vger.kernel.org>
Reported-by: Krzysztof Rusocki <krzysztof.rusocki@intel.com>
Reported-by: Vishal Verma <vishal.l.verma@intel.com>
Reviewed-by: Toshi Kani <toshi.kani@hpe.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/acpi/nfit/core.c

@@ -2652,7 +2652,10 @@ static int ars_start(struct acpi_nfit_desc *acpi_desc,
 
 	if (rc < 0)
 		return rc;
-	return cmd_rc;
+	if (cmd_rc < 0)
+		return cmd_rc;
+	set_bit(ARS_VALID, &acpi_desc->scrub_flags);
+	return 0;
 }
 
 static int ars_continue(struct acpi_nfit_desc *acpi_desc)
@@ -2745,6 +2748,17 @@ static int ars_status_process_records(struct acpi_nfit_desc *acpi_desc)
 	 */
 	if (ars_status->out_length < 44)
 		return 0;
+
+	/*
+	 * Ignore potentially stale results that are only refreshed
+	 * after a start-ARS event.
+	 */
+	if (!test_and_clear_bit(ARS_VALID, &acpi_desc->scrub_flags)) {
+		dev_dbg(acpi_desc->dev, "skip %d stale records\n",
+				ars_status->num_records);
+		return 0;
+	}
+
 	for (i = 0; i < ars_status->num_records; i++) {
 		/* only process full records */
 		if (ars_status->out_length
@@ -3229,6 +3243,7 @@ static int acpi_nfit_register_regions(struct acpi_nfit_desc *acpi_desc)
 	struct nfit_spa *nfit_spa;
 	int rc;
 
+	set_bit(ARS_VALID, &acpi_desc->scrub_flags);
 	list_for_each_entry(nfit_spa, &acpi_desc->spas, list) {
 		switch (nfit_spa_type(nfit_spa->spa)) {
 		case NFIT_SPA_VOLATILE:

drivers/acpi/nfit/nfit.h

@@ -213,6 +213,7 @@ struct nfit_mem {
 enum scrub_flags {
 	ARS_BUSY,
 	ARS_CANCEL,
+	ARS_VALID,
 	ARS_POLL,
 };