Introduce unified API to zero memory

Introduce zeromem_dczva function on AArch64 that can handle unaligned
addresses and make use of DC ZVA instruction to zero a whole block at a
time. This zeroing takes place directly in the cache to speed it up
without doing external memory access.

Remove the zeromem16 function on AArch64 and replace it with an alias to
zeromem. This zeromem16 function is now deprecated.

Remove the 16-bytes alignment constraint on __BSS_START__ in
firmware-design.md as it is now not mandatory anymore (it used to comply
with zeromem16 requirements).

Change the 16-bytes alignment constraints in SP min's linker script to a
8-bytes alignment constraint as the AArch32 zeromem implementation is now
more efficient on 8-bytes aligned addresses.

Introduce zero_normalmem and zeromem helpers in platform agnostic header
that are implemented this way:
* AArch32:
	* zero_normalmem: zero using usual data access
	* zeromem: alias for zero_normalmem
* AArch64:
	* zero_normalmem: zero normal memory  using DC ZVA instruction
	                  (needs MMU enabled)
	* zeromem: zero using usual data access

Usage guidelines: in most cases, zero_normalmem should be preferred.

There are 2 scenarios where zeromem (or memset) must be used instead:
* Code that must run with MMU disabled (which means all memory is
  considered device memory for data accesses).
* Code that fills device memory with null bytes.

Optionally, the following rule can be applied if performance is
important:
* Code zeroing small areas (few bytes) that are not secrets should use
  memset to take advantage of compiler optimizations.

  Note: Code zeroing security-related critical information should use
  zero_normalmem/zeromem instead of memset to avoid removal by
  compilers' optimizations in some cases or misbehaving versions of GCC.

Fixes ARM-software/tf-issues#408

Change-Id: Iafd9663fc1070413c3e1904e54091cf60effaa82
Signed-off-by: Douglas Raillard <douglas.raillard@arm.com>

2 files changed, 34 insertions, 3 deletions

diff --git a/include/common/aarch64/el3_common_macros.S b/include/common/aarch64/el3_common_macros.S
index cbfa6eec..2e70fc2e 100644
--- a/include/common/aarch64/el3_common_macros.S
+++ b/include/common/aarch64/el3_common_macros.S
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015-2016, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2015-2017, ARM Limited and Contributors. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
@@ -252,12 +252,12 @@
 
 		ldr	x0, =__BSS_START__
 		ldr	x1, =__BSS_SIZE__
-		bl	zeromem16
+		bl	zeromem
 
 #if USE_COHERENT_MEM
 		ldr	x0, =__COHERENT_RAM_START__
 		ldr	x1, =__COHERENT_RAM_UNALIGNED_SIZE__
-		bl	zeromem16
+		bl	zeromem
 #endif
 
 #ifdef IMAGE_BL1
diff --git a/include/lib/utils.h b/include/lib/utils.h
index b6bc9af6..69bbb430 100644
--- a/include/lib/utils.h
+++ b/include/lib/utils.h
@@ -80,4 +80,35 @@
 # define ULL(_x)	(_x##ull)
 #endif
 
+/*
+ * C code should be put in this part of the header to avoid breaking ASM files
+ * or linker scripts including it.
+ */
+#if !(defined(__LINKER__) || defined(__ASSEMBLY__))
+
+#include <types.h>
+
+/*
+ * Fill a region of normal memory of size "length" in bytes with zero bytes.
+ *
+ * WARNING: This function can only operate on normal memory. This means that
+ *          the MMU must be enabled when using this function. Otherwise, use
+ *          zeromem.
+ */
+void zero_normalmem(void *mem, u_register_t length);
+
+/*
+ * Fill a region of memory of size "length" in bytes with null bytes.
+ *
+ * Unlike zero_normalmem, this function has no restriction on the type of
+ * memory targeted and can be used for any device memory as well as normal
+ * memory. This function must be used instead of zero_normalmem when MMU is
+ * disabled.
+ *
+ * NOTE: When data cache and MMU are enabled, prefer zero_normalmem for faster
+ *       zeroing.
+ */
+void zeromem(void *mem, u_register_t length);
+#endif /* !(defined(__LINKER__) || defined(__ASSEMBLY__)) */
+
 #endif /* __UTILS_H__ */