plat/common: Do not insert left region empty leftover on overlap

Consider the following case:
|-----------|----------|---------------|
|           |          |               |
|-----------|----------|---------------|
ML start    MR start   MR end          ML end

In the current state, we insert the (ML end - MR end) region regardless
of its length. If it is equal to 0, we end up inserting an empty memory
region. Thus, do not do this insertion if (ML end - MR end) == 0.

Signed-off-by: Sergiu Moga <sergiu@unikraft.io>
Reviewed-by: Michalis Pappas <michalis@unikraft.io>
Approved-by: Razvan Deaconescu <razvand@unikraft.io>
GitHub-Closes: #1060

diff --git a/plat/common/memory.c b/plat/common/memory.c
index 016baa1b954b461cb525a8f809bb679d06af7327..a46f1344568b1aed2a1c4b464f7fa5922e7baa4b 100644 (file)
--- a/plat/common/memory.c
+++ b/plat/common/memory.c
@@ -180,6 +180,8 @@ static inline int get_mrd_prio(struct ukplat_memregion_desc *const m)
  * contains the right memory region of higher priority, then split the left one
  * in two, by adjusting the current left one and inserting a new memory region
  * descriptor.
+ * The start of the left memory region in the list is always less
+ * or equal to the start of the right memory region in the list.
  */
 static inline void overlapping_mrd_fixup(struct ukplat_memregion_list *list,
                                         struct ukplat_memregion_desc *const ml,
@@ -217,22 +219,27 @@ static inline void overlapping_mrd_fixup(struct ukplat_memregion_list *list,
                 * a new one if the left region is larger than the right region.
                 */
                } else {
+                       __sz len = ml->pbase + ml->len - mr->pbase - mr->len;
+
                        if (RANGE_CONTAIN(ml->pbase, ml->len,
-                                         mr->pbase, mr->len))
-                               /* Ignore insertion failure as there is nothing
-                                * we can do about it and it is not worth caring
-                                * about.
+                                         mr->pbase, mr->len && len))
+                               /* len here is basically ml_end - mr_end. Thus,
+                                * len == 0 can happen only if mr is at the end
+                                * of the ml and we therefore ignore the rest.
+                                * If we ended up here then mr is actually
+                                * somewhere in the middle of ml and we are
+                                * inserting the mrd between mr_end and ml_end
                                 */
                                ukplat_memregion_list_insert_at_idx(list,
                                        &(struct ukplat_memregion_desc){
                                                .vbase = mr->pbase + mr->len,
                                                .pbase = mr->pbase + mr->len,
-                                               .len   = ml->pbase + ml->len -
-                                                        mr->pbase - mr->len,
+                                               .len   = len,
                                                .type  = ml->type,
                                                .flags = ml->flags
                                        }, ridx + 1);
 
+                       /* Drop the fraction of ml that overlaps with mr */
                        ml->len = mr->pbase - ml->pbase;
                }
        }
@@ -279,6 +286,8 @@ static void ukplat_memregion_restore_mrd(struct ukplat_memregion_desc *mrd,
 /* Quick function to do potentially necessary swapping of two adjacent memory
  * region descriptors. Here just to modularize code because
  * ukplat_memregion_list_coalesce was quite large already.
+ * Guarantees the start of the left memory region in the list is always less
+ * or equal to the start of the right memory region in the list.
  */
 static void ukplat_memregion_swap_if_unordered(struct ukplat_memregion_list *l,
                                               __u32 l_idx, __u32 r_idx)