FROMLIST: memblock: handle overlapped reserved memory region

It is not common, but defining an overlapped region is possible.
Actually memblock_add_range allows to overlap with existing ones.

The memsize currently does not handle this overlapped case. But this
patch tries to handle one overlapped case.

Here's the case.

There is an unknown memsize region, which means the region was removed
and not passed at bootloader stage. And there is a reserved memory
region defined in device tree which is overlapped with the unknown
region.

We expect that information in device tree make the unknown region clear.
This patch handle the overlapped region with following conditions.

1) The already existing overlapped region should be unknown and no-map.
2) The newly added region should have a name, and its region should be
same with or part of the existing one.

Here is an example.

Before this patch, memsize shows both overlapped region.

0x0ea000000-0x0ed900000 0x03900000 (   58368 KB ) nomap unusable overlapped
0x0ea000000-0x0f1400000 0x07400000 (  118784 KB ) nomap unusable unknown

After this patch, the overlapped region is named.

0x0ea000000-0x0ed900000 0x03900000 (   58368 KB ) nomap unusable overlapped
0x0e9b00000-0x0ea000000 0x00500000 (    5120 KB ) nomap unusable unknown

Bug: 340432773
Signed-off-by: Jaewon Kim <jaewon31.kim@samsung.com>
Link: https://lore.kernel.org/linux-mm/20240521023957.2587005-4-jaewon31.kim@samsung.com/
Change-Id: I7091eedcebd1f2f771124c157e5e00600b9a36fd

mm/memblock.c

@@ -1993,6 +1993,65 @@ static void memsize_get_valid_name(char *valid_name, const char *name)
 	valid_name[val_size] = '\0';
 }
 
+static inline struct memsize_rgn_struct * __init_memblock memsize_get_new_rgn(void)
+{
+	if (memsize_rgn_count == ARRAY_SIZE(memsize_rgn)) {
+		pr_err("not enough space on memsize_rgn\n");
+		return NULL;
+	}
+	return &memsize_rgn[memsize_rgn_count++];
+}
+static bool __init_memblock memsize_update_nomap_region(const char *name, phys_addr_t base,
+					phys_addr_t size, bool nomap)
+{
+	int i;
+	struct memsize_rgn_struct *rmem_rgn, *new_rgn;
+	if (!name)
+		return false;
+	for (i = 0; i < memsize_rgn_count; i++)	{
+		rmem_rgn = &memsize_rgn[i];
+		if (!rmem_rgn->nomap)
+			continue;
+		if (strcmp(rmem_rgn->name, "unknown"))
+			continue;
+		if (base < rmem_rgn->base)
+			continue;
+		if (base + size > rmem_rgn->base + rmem_rgn->size)
+			continue;
+		if (base == rmem_rgn->base && size == rmem_rgn->size) {
+			memsize_get_valid_name(rmem_rgn->name, name);
+			return true;
+		}
+		new_rgn = memsize_get_new_rgn();
+		if (!new_rgn)
+			return true;
+		new_rgn->base = base;
+		new_rgn->size = size;
+		new_rgn->nomap = nomap;
+		new_rgn->reusable = false;
+		memsize_get_valid_name(new_rgn->name, name);
+		if (base == rmem_rgn->base && size < rmem_rgn->size) {
+			rmem_rgn->base = base + size;
+			rmem_rgn->size -= size;
+		} else if (base + size == rmem_rgn->base + rmem_rgn->size) {
+			rmem_rgn->size -= size;
+		} else {
+			new_rgn = memsize_get_new_rgn();
+			if (!new_rgn)
+				return true;
+			new_rgn->base = base + size;
+			new_rgn->size = (rmem_rgn->base + rmem_rgn->size)
+					- (base + size);
+			new_rgn->nomap = nomap;
+			new_rgn->reusable = false;
+			strscpy(new_rgn->name, "unknown", sizeof(new_rgn->name));
+			rmem_rgn->size = base - rmem_rgn->base;
+		}
+		return true;
+	}
+	return false;
+}
+
 void memblock_memsize_record(const char *name, phys_addr_t base,
 			     phys_addr_t size, bool nomap, bool reusable)
 {
@@ -2005,7 +2064,11 @@ void memblock_memsize_record(const char *name, phys_addr_t base,
 	}
 	memblock_dbg("%s %pa..%pa nomap:%d reusable:%d\n",
 		     __func__, &base, &end, nomap, reusable);
-	rgn = &memsize_rgn[memsize_rgn_count++];
+	if (memsize_update_nomap_region(name, base, size, nomap))
+		return;
+	rgn = memsize_get_new_rgn();
+	if (!rgn)
+		return;
 	rgn->base = base;
 	rgn->size = size;
 	rgn->nomap = nomap;