xlat: Introduce MAP_REGION2() macro
The current implementation of the memory mapping API favours mapping
memory regions using the biggest possible block size in order to
reduce the number of translation tables needed.
In some cases, this behaviour might not be desirable. When translation
tables are edited at run-time, coarse-grain mappings like that might
need splitting into finer-grain tables. This operation has a
performance cost.
The MAP_REGION2() macro allows to specify the granularity of
translation tables used for the initial mapping of a memory region.
This might increase performance for memory regions that are likely to
be edited in the future, at the expense of a potentially increased
memory footprint.
The Translation Tables Library Design Guide has been updated to
explain the use case for this macro. Also added a few intermediate
titles to make the guide easier to digest.
Change-Id: I04de9302e0ee3d326b8877043a9f638766b81b7b
Co-authored-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
Co-authored-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
diff --git a/include/lib/xlat_tables/xlat_tables_v2.h b/include/lib/xlat_tables/xlat_tables_v2.h
index 59f0955..a4f0efd 100644
--- a/include/lib/xlat_tables/xlat_tables_v2.h
+++ b/include/lib/xlat_tables/xlat_tables_v2.h
@@ -15,20 +15,36 @@
#include <xlat_mmu_helpers.h>
#include <xlat_tables_v2_helpers.h>
-/* Helper macro to define entries for mmap_region_t. It creates
- * identity mappings for each region.
+/*
+ * Default granularity size for an mmap_region_t.
+ * Useful when no specific granularity is required.
+ *
+ * By default, choose the biggest possible block size allowed by the
+ * architectural state and granule size in order to minimize the number of page
+ * tables required for the mapping.
*/
-#define MAP_REGION_FLAT(adr, sz, attr) MAP_REGION(adr, adr, sz, attr)
+#define REGION_DEFAULT_GRANULARITY XLAT_BLOCK_SIZE(MIN_LVL_BLOCK_DESC)
+
+/* Helper macro to define an mmap_region_t. */
+#define MAP_REGION(_pa, _va, _sz, _attr) \
+ _MAP_REGION_FULL_SPEC(_pa, _va, _sz, _attr, REGION_DEFAULT_GRANULARITY)
-/* Helper macro to define entries for mmap_region_t. It allows to
- * re-map address mappings from 'pa' to 'va' for each region.
+/* Helper macro to define an mmap_region_t with an identity mapping. */
+#define MAP_REGION_FLAT(_adr, _sz, _attr) \
+ MAP_REGION(_adr, _adr, _sz, _attr)
+
+/*
+ * Helper macro to define an mmap_region_t to map with the desired granularity
+ * of translation tables.
+ *
+ * The granularity value passed to this macro must be a valid block or page
+ * size. When using a 4KB translation granule, this might be 4KB, 2MB or 1GB.
+ * Passing REGION_DEFAULT_GRANULARITY is also allowed and means that the library
+ * is free to choose the granularity for this region. In this case, it is
+ * equivalent to the MAP_REGION() macro.
*/
-#define MAP_REGION(_pa, _va, _sz, _attr) { \
- .base_pa = (_pa), \
- .base_va = (_va), \
- .size = (_sz), \
- .attr = (_attr), \
- }
+#define MAP_REGION2(_pa, _va, _sz, _attr, _gr) \
+ _MAP_REGION_FULL_SPEC(_pa, _va, _sz, _attr, _gr)
/*
* Shifts and masks to access fields of an mmap_attr_t
@@ -86,6 +102,8 @@
uintptr_t base_va;
size_t size;
mmap_attr_t attr;
+ /* Desired granularity. See the MAP_REGION2() macro for more details. */
+ size_t granularity;
} mmap_region_t;
/*
diff --git a/include/lib/xlat_tables/xlat_tables_v2_helpers.h b/include/lib/xlat_tables/xlat_tables_v2_helpers.h
index f5e3100..1ea2fc0 100644
--- a/include/lib/xlat_tables/xlat_tables_v2_helpers.h
+++ b/include/lib/xlat_tables/xlat_tables_v2_helpers.h
@@ -27,6 +27,20 @@
/* Forward declaration */
struct mmap_region;
+/*
+ * Helper macro to define an mmap_region_t. This macro allows to specify all
+ * the fields of the structure but its parameter list is not guaranteed to
+ * remain stable as we add members to mmap_region_t.
+ */
+#define _MAP_REGION_FULL_SPEC(_pa, _va, _sz, _attr, _gr) \
+ { \
+ .base_pa = (_pa), \
+ .base_va = (_va), \
+ .size = (_sz), \
+ .attr = (_attr), \
+ .granularity = (_gr), \
+ }
+
/* Struct that holds all information about the translation tables. */
struct xlat_ctx {
/*