Add comments about mismatched TCR_ELx and xlat tables

When the MMU is enabled and the translation tables are mapped, data
read/writes to the translation tables are made using the attributes
specified in the translation tables themselves. However, the MMU
performs table walks with the attributes specified in TCR_ELx. They are
completely independent, so special care has to be taken to make sure
that they are the same.

This has to be done manually because it is not practical to have a test
in the code. Such a test would need to know the virtual memory region
that contains the translation tables and check that for all of the
tables the attributes match the ones in TCR_ELx. As the tables may not
even be mapped at all, this isn't a test that can be made generic.

The flags used by enable_mmu_xxx() have been moved to the same header
where the functions are.

Also, some comments in the linker scripts related to the translation
tables have been fixed.

Change-Id: I1754768bffdae75f53561b1c4a5baf043b45a304
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>

2 files changed, 42 insertions, 15 deletions

diff --git a/include/lib/xlat_tables/xlat_mmu_helpers.h b/include/lib/xlat_tables/xlat_mmu_helpers.h
index fd3efc3f..d83d7640 100644
--- a/include/lib/xlat_tables/xlat_mmu_helpers.h
+++ b/include/lib/xlat_tables/xlat_mmu_helpers.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014-2017, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2014-2018, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -7,13 +7,51 @@
 #ifndef __XLAT_MMU_HELPERS_H__
 #define __XLAT_MMU_HELPERS_H__
 
+/*
+ * The following flags are passed to enable_mmu_xxx() to override the default
+ * values used to program system registers while enabling the MMU.
+ */
+
+/*
+ * When this flag is used, all data access to Normal memory from this EL and all
+ * Normal memory accesses to the translation tables of this EL are non-cacheable
+ * for all levels of data and unified cache until the caches are enabled by
+ * setting the bit SCTLR_ELx.C.
+ */
+#define DISABLE_DCACHE			(U(1) << 0)
+
+/*
+ * Mark the translation tables as non-cacheable for the MMU table walker, which
+ * is a different observer from the PE/CPU. If the flag is not specified, the
+ * tables are cacheable for the MMU table walker.
+ *
+ * Note that, as far as the PE/CPU observer is concerned, the attributes used
+ * are the ones specified in the translation tables themselves. The MAIR
+ * register specifies the cacheability through the field AttrIndx of the lower
+ * attributes of the translation tables. The shareability is specified in the SH
+ * field of the lower attributes.
+ *
+ * The MMU table walker uses the attributes specified in the fields ORGNn, IRGNn
+ * and SHn of the TCR register to access the translation tables.
+ *
+ * The attributes specified in the TCR register and the tables can be different
+ * as there are no checks to prevent that. Special care must be taken to ensure
+ * that there aren't mismatches. The behaviour in that case is described in the
+ * sections 'Mismatched memory attributes' in the ARMv8 ARM.
+ */
+#define XLAT_TABLE_NC			(U(1) << 1)
+
+#ifndef __ASSEMBLY__
+
 #ifdef AARCH32
 /* AArch32 specific translation table API */
-void enable_mmu_secure(uint32_t flags);
+void enable_mmu_secure(unsigned int flags);
 #else
 /* AArch64 specific translation table APIs */
 void enable_mmu_el1(unsigned int flags);
 void enable_mmu_el3(unsigned int flags);
 #endif /* AARCH32 */
 
+#endif /* __ASSEMBLY__ */
+
 #endif /* __XLAT_MMU_HELPERS_H__ */
diff --git a/include/lib/xlat_tables/xlat_tables_defs.h b/include/lib/xlat_tables/xlat_tables_defs.h
index 3a7f2456..1c84fe07 100644
--- a/include/lib/xlat_tables/xlat_tables_defs.h
+++ b/include/lib/xlat_tables/xlat_tables_defs.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2017-2018, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -9,6 +9,7 @@
 
 #include <arch.h>
 #include <utils_def.h>
+#include <xlat_mmu_helpers.h>
 
 /* Miscellaneous MMU related constants */
 #define NUM_2MB_IN_GB		(U(1) << 9)
@@ -165,16 +166,4 @@
 #define XN_SHIFT			54
 #define UXN_SHIFT			XN_SHIFT
 
-/*
- * Flags to override default values used to program system registers while
- * enabling the MMU.
- */
-#define DISABLE_DCACHE			(U(1) << 0)
-
-/*
- * This flag marks the translation tables are Non-cacheable for MMU accesses.
- * If the flag is not specified, by default the tables are cacheable.
- */
-#define XLAT_TABLE_NC			(U(1) << 1)
-
 #endif /* __XLAT_TABLES_DEFS_H__ */