ACPI / tables: Convert initrd table override to table upgrade mechanism

This patch converts the initrd table override mechanism to the table
upgrade mechanism by restricting its usage to the tables released with
compatibility and more recent revision.

This use case has been encouraged by the ACPI specification:

 1. OEMID:
    An OEM-supplied string that identifies the OEM.

 2. OEM Table ID:
    An OEM-supplied string that the OEM uses to identify the particular data
    table. This field is particularly useful when defining a definition
    block to distinguish definition block functions. OEM assigns each
    dissimilar table a new OEM Table Id.

 3. OEM Revision:
    An OEM-supplied revision number. Larger numbers are assumed to be newer
    revisions.

For OEMs, good practices will ensure consistency when assigning OEMID and
OEM Table ID fields in any table. The intent of these fields is to allow
for a binary control system that support services can use. Because many
support function can be automated, it is useful when a tool can
programatically determine which table release is a compatible and more
recent revision of a prior table on the same OEMID and OEM Table ID.

The facility can now be used by the vendors to upgrade wrong tables for bug
fixing purpose, thus lockdep disabling taint is not suitable for it and it
should be a default 'y' option to implement the spec encouraged use case.

Note that, by implementing table upgrade inside of ACPICA itself, it is
possible to remove acpi_table_initrd_override() and tables can be upgraded
by acpi_install_table() automatically. Though current ACPICA impelentation
hasn't implemented this, this patched changes the table flag setting timing
to allow this to be implemented in ACPICA without changing the code here.

Documentation of initrd override mechanism is upgraded accordingly.

Original-by: Octavian Purdila <octavian.purdila@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

2 files changed, 38 insertions, 18 deletions

diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index 82b96ee8624c..b225c4b9ba14 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -311,12 +311,12 @@ config ACPI_CUSTOM_DSDT
 	bool
 	default ACPI_CUSTOM_DSDT_FILE != ""
 
-config ACPI_INITRD_TABLE_OVERRIDE
-	bool "ACPI tables override via initrd"
+config ACPI_TABLE_UPGRADE
+	bool "Allow upgrading ACPI tables via initrd"
 	depends on BLK_DEV_INITRD && X86
-	default n
+	default y
 	help
-	  This option provides functionality to override arbitrary ACPI tables
+	  This option provides functionality to upgrade arbitrary ACPI tables
 	  via initrd. No functional change if no ACPI tables are passed via
 	  initrd, therefore it's safe to say Y.
 	  See Documentation/acpi/initrd_table_override.txt for details
diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
index 2e74dbf45dd4..08795fbde3fa 100644
--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -442,7 +442,7 @@ static void acpi_table_taint(struct acpi_table_header *table)
 	add_taint(TAINT_OVERRIDDEN_ACPI_TABLE, LOCKDEP_NOW_UNRELIABLE);
 }
 
-#ifdef CONFIG_ACPI_INITRD_TABLE_OVERRIDE
+#ifdef CONFIG_ACPI_TABLE_UPGRADE
 static u64 acpi_tables_addr;
 static int all_tables_size;
 
@@ -471,9 +471,9 @@ static const char * const table_sigs[] = {
 
 #define ACPI_HEADER_SIZE sizeof(struct acpi_table_header)
 
-#define ACPI_OVERRIDE_TABLES 64
-static struct cpio_data __initdata acpi_initrd_files[ACPI_OVERRIDE_TABLES];
-static DECLARE_BITMAP(acpi_initrd_installed, ACPI_OVERRIDE_TABLES);
+#define NR_ACPI_INITRD_TABLES 64
+static struct cpio_data __initdata acpi_initrd_files[NR_ACPI_INITRD_TABLES];
+static DECLARE_BITMAP(acpi_initrd_installed, NR_ACPI_INITRD_TABLES);
 
 #define MAP_CHUNK_SIZE   (NR_FIX_BTMAPS << PAGE_SHIFT)
 
@@ -488,7 +488,7 @@ static void __init acpi_table_initrd_init(void *data, size_t size)
 	if (data == NULL || size == 0)
 		return;
 
-	for (no = 0; no < ACPI_OVERRIDE_TABLES; no++) {
+	for (no = 0; no < NR_ACPI_INITRD_TABLES; no++) {
 		file = find_cpio_data(cpio_path, data, size, &offset);
 		if (!file.data)
 			break;
@@ -611,19 +611,30 @@ acpi_table_initrd_override(struct acpi_table_header *existing_table,
 		table_length = table->length;
 
 		/* Only override tables matched */
-		if (test_bit(table_index, acpi_initrd_installed) ||
-		    memcmp(existing_table->signature, table->signature, 4) ||
+		if (memcmp(existing_table->signature, table->signature, 4) ||
+		    memcmp(table->oem_id, existing_table->oem_id,
+			   ACPI_OEM_ID_SIZE) ||
 		    memcmp(table->oem_table_id, existing_table->oem_table_id,
 			   ACPI_OEM_TABLE_ID_SIZE)) {
 			acpi_os_unmap_memory(table, ACPI_HEADER_SIZE);
 			goto next_table;
 		}
+		/*
+		 * Mark the table to avoid being used in
+		 * acpi_table_initrd_scan() and check the revision.
+		 */
+		if (test_and_set_bit(table_index, acpi_initrd_installed) ||
+		    existing_table->oem_revision >= table->oem_revision) {
+			acpi_os_unmap_memory(table, ACPI_HEADER_SIZE);
+			goto next_table;
+		}
 
 		*length = table_length;
 		*address = acpi_tables_addr + table_offset;
-		acpi_table_taint(existing_table);
+		pr_info("Table Upgrade: override [%4.4s-%6.6s-%8.8s]\n",
+			table->signature, table->oem_id,
+			table->oem_table_id);
 		acpi_os_unmap_memory(table, ACPI_HEADER_SIZE);
-		set_bit(table_index, acpi_initrd_installed);
 		break;
 
 next_table:
@@ -655,17 +666,26 @@ static void __init acpi_table_initrd_scan(void)
 		table_length = table->length;
 
 		/* Skip RSDT/XSDT which should only be used for override */
-		if (test_bit(table_index, acpi_initrd_installed) ||
-		    ACPI_COMPARE_NAME(table->signature, ACPI_SIG_RSDT) ||
+		if (ACPI_COMPARE_NAME(table->signature, ACPI_SIG_RSDT) ||
 		    ACPI_COMPARE_NAME(table->signature, ACPI_SIG_XSDT)) {
 			acpi_os_unmap_memory(table, ACPI_HEADER_SIZE);
 			goto next_table;
 		}
+		/*
+		 * Mark the table to avoid being used in
+		 * acpi_table_initrd_override(). Though this is not possible
+		 * because override is disabled in acpi_install_table().
+		 */
+		if (test_and_set_bit(table_index, acpi_initrd_installed)) {
+			acpi_os_unmap_memory(table, ACPI_HEADER_SIZE);
+			goto next_table;
+		}
 
-		acpi_table_taint(table);
+		pr_info("Table Upgrade: install [%4.4s-%6.6s-%8.8s]\n",
+			table->signature, table->oem_id,
+			table->oem_table_id);
 		acpi_os_unmap_memory(table, ACPI_HEADER_SIZE);
 		acpi_install_table(acpi_tables_addr + table_offset, TRUE);
-		set_bit(table_index, acpi_initrd_installed);
 next_table:
 		table_offset += table_length;
 		table_index++;
@@ -689,7 +709,7 @@ acpi_table_initrd_override(struct acpi_table_header *existing_table,
 static void __init acpi_table_initrd_scan(void)
 {
 }
-#endif /* CONFIG_ACPI_INITRD_TABLE_OVERRIDE */
+#endif /* CONFIG_ACPI_TABLE_UPGRADE */
 
 acpi_status
 acpi_os_physical_table_override(struct acpi_table_header *existing_table,