+ const s64 linear_region_size = -(s64)PAGE_OFFSET;
+
+ /*
+ * Ensure that the linear region takes up exactly half of the kernel
+ * virtual address space. This way, we can distinguish a linear address
+ * from a kernel/module/vmalloc address by testing a single bit.
+ */
+ BUILD_BUG_ON(linear_region_size != BIT(VA_BITS - 1));
+
+ /*
+ * Select a suitable value for the base of physical memory.
+ */
+ memstart_addr = round_down(memblock_start_of_DRAM(),
+ ARM64_MEMSTART_ALIGN);
+
+ /*
+ * Remove the memory that we will not be able to cover with the
+ * linear mapping. Take care not to clip the kernel which may be
+ * high in memory.
+ */
+ memblock_remove(max_t(u64, memstart_addr + linear_region_size, __pa(_end)),
+ ULLONG_MAX);
+ if (memblock_end_of_DRAM() > linear_region_size)
+ memblock_remove(0, memblock_end_of_DRAM() - linear_region_size);
+
+ /*
+ * Apply the memory limit if it was set. Since the kernel may be loaded
+ * high up in memory, add back the kernel region that must be accessible
+ * via the linear mapping.
+ */
+ if (memory_limit != (phys_addr_t)ULLONG_MAX) {
+ memblock_enforce_memory_limit(memory_limit);
+ memblock_add(__pa(_text), (u64)(_end - _text));
+ }
+
+ if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
+ extern u16 memstart_offset_seed;
+ u64 range = linear_region_size -
+ (memblock_end_of_DRAM() - memblock_start_of_DRAM());
+
+ /*
+ * If the size of the linear region exceeds, by a sufficient
+ * margin, the size of the region that the available physical
+ * memory spans, randomize the linear region as well.
+ */
+ if (memstart_offset_seed > 0 && range >= ARM64_MEMSTART_ALIGN) {
+ range = range / ARM64_MEMSTART_ALIGN + 1;
+ memstart_addr -= ARM64_MEMSTART_ALIGN *
+ ((range * memstart_offset_seed) >> 16);
+ }
+ }