mm/memblock: add MEMBLOCK_NOMAP attribute to memblock memory table

This introduces the MEMBLOCK_NOMAP attribute and the required plumbing
to make it usable as an indicator that some parts of normal memory
should not be covered by the kernel direct mapping. It is up to the
arch to actually honor the attribute when laying out this mapping,
but the memblock code itself is modified to disregard these regions
for allocations and other general use.

Cc: [e-mail]
Cc: Alexander Kuleshov <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Reviewed-by: Matt Fleming <[e-mail]>
Signed-off-by: Ard Biesheuvel <[e-mail]>
Signed-off-by: Will Deacon <[e-mail]>

include/linux/memblock.h

···
 	MEMBLOCK_NONE		= 0x0,	/* No special request */
 	MEMBLOCK_HOTPLUG	= 0x1,	/* hotpluggable region */
 	MEMBLOCK_MIRROR		= 0x2,	/* mirrored region */
+	MEMBLOCK_NOMAP		= 0x4,	/* don't add to kernel direct mapping */
 };
 
 struct memblock_region {
···
 int memblock_mark_hotplug(phys_addr_t base, phys_addr_t size);
 int memblock_clear_hotplug(phys_addr_t base, phys_addr_t size);
 int memblock_mark_mirror(phys_addr_t base, phys_addr_t size);
+int memblock_mark_nomap(phys_addr_t base, phys_addr_t size);
 ulong choose_memblock_flags(void);
 
 /* Low level functions */
···
 static inline bool memblock_is_mirror(struct memblock_region *m)
 {
 	return m->flags & MEMBLOCK_MIRROR;
+}
+
+static inline bool memblock_is_nomap(struct memblock_region *m)
+{
+	return m->flags & MEMBLOCK_NOMAP;
 }
 
 #ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
···
 phys_addr_t memblock_end_of_DRAM(void);
 void memblock_enforce_memory_limit(phys_addr_t memory_limit);
 int memblock_is_memory(phys_addr_t addr);
+int memblock_is_map_memory(phys_addr_t addr);
 int memblock_is_region_memory(phys_addr_t base, phys_addr_t size);
 int memblock_is_reserved(phys_addr_t addr);
 bool memblock_is_region_reserved(phys_addr_t base, phys_addr_t size);

mm/memblock.c

···
 	return memblock_setclr_flag(base, size, 1, MEMBLOCK_MIRROR);
 }
 
+/**
+ * memblock_mark_nomap - Mark a memory region with flag MEMBLOCK_NOMAP.
+ * @base: the base phys addr of the region
+ * @size: the size of the region
+ *
+ * Return 0 on success, -errno on failure.
+ */
+int __init_memblock memblock_mark_nomap(phys_addr_t base, phys_addr_t size)
+{
+	return memblock_setclr_flag(base, size, 1, MEMBLOCK_NOMAP);
+}
 
 /**
  * __next_reserved_mem_region - next function for for_each_reserved_region()
···
 
 		/* if we want mirror memory skip non-mirror memory regions */
 		if ((flags & MEMBLOCK_MIRROR) && !memblock_is_mirror(m))
+			continue;
+
+		/* skip nomap memory unless we were asked for it explicitly */
+		if (!(flags & MEMBLOCK_NOMAP) && memblock_is_nomap(m))
 			continue;
 
 		if (!type_b) {
···
 
 		/* if we want mirror memory skip non-mirror memory regions */
 		if ((flags & MEMBLOCK_MIRROR) && !memblock_is_mirror(m))
+			continue;
+
+		/* skip nomap memory unless we were asked for it explicitly */
+		if (!(flags & MEMBLOCK_NOMAP) && memblock_is_nomap(m))
 			continue;
 
 		if (!type_b) {
···
 int __init_memblock memblock_is_memory(phys_addr_t addr)
 {
 	return memblock_search(&memblock.memory, addr) != -1;
+}
+
+int __init_memblock memblock_is_map_memory(phys_addr_t addr)
+{
+	int i = memblock_search(&memblock.memory, addr);
+
+	if (i == -1)
+		return false;
+	return !memblock_is_nomap(&memblock.memory.regions[i]);
 }
 
 #ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP