ANDROID: arm64/mm: implement {populate/depopulate}_range_driver_managed

After certain memory blocks are offlined, some usecases require that the
page-table mappings are removed while still keeping the memblock device nodes,
memory resources and the memmap entries intact. This is to avoid the overhead
involved in using 'remove_memory' if the offlined blocks will be added/onlined
back into the system at later point. {populate/depopulate}_range_driver_managed
provide the abilty to drivers to tear-down and create page-table mappings of
memory blocks that its managing, without having to use 'remove_memory' and
friends for the purpose.
These functions does not interfere with mappings of boot memory or resources
that isn't owned by the driver.

Bug: 171907330
Change-Id: Ie11201334bd7438bf87f933ccc81814fa99162c4
Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org>

arch/arm64/include/asm/pgtable.h

@@ -530,6 +530,13 @@ extern pgd_t tramp_pg_dir[PTRS_PER_PGD];
 
 extern void set_swapper_pgd(pgd_t *pgdp, pgd_t pgd);
 
+#ifdef CONFIG_MEMORY_HOTPLUG
+extern int populate_range_driver_managed(u64 start, u64 size,
+		const char *resource_name);
+extern int depopulate_range_driver_managed(u64 start, u64 size,
+		const char *resource_name);
+#endif
+
 static inline bool in_swapper_pgdir(void *addr)
 {
 	return ((unsigned long)addr & PAGE_MASK) ==

arch/arm64/mm/mmu.c

@@ -1496,6 +1496,71 @@ void arch_remove_memory(int nid, u64 start, u64 size,
 	__remove_pgd_mapping(swapper_pg_dir, __phys_to_virt(start), size);
 }
 
+int check_range_driver_managed(u64 start, u64 size, const char *resource_name)
+{
+	struct mem_section *ms;
+	unsigned long pfn = __phys_to_pfn(start);
+	unsigned long end_pfn = __phys_to_pfn(start + size);
+	struct resource *res;
+	unsigned long flags;
+
+	res = lookup_resource(&iomem_resource, start);
+	if (!res) {
+		pr_err("%s: couldn't find memory resource for start 0x%lx\n",
+			   __func__, start);
+		return -EINVAL;
+	}
+
+	flags = res->flags;
+
+	if (!(flags & IORESOURCE_SYSRAM_DRIVER_MANAGED) ||
+	    strstr(resource_name, "System RAM (") != resource_name)
+		return -EINVAL;
+
+	for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
+		ms = __pfn_to_section(pfn);
+		if (early_section(ms))
+			return -EINVAL;
+	}
+
+	return 0;
+}
+
+int populate_range_driver_managed(u64 start, u64 size,
+			const char *resource_name)
+{
+	unsigned long virt = (unsigned long)phys_to_virt(start);
+	int flags = 0;
+
+	if (check_range_driver_managed(start, size, resource_name))
+		return -EINVAL;
+
+	/*
+	 * When rodata_full is enabled, memory is mapped at page size granule,
+	 * as opposed to block mapping.
+	 */
+	if (rodata_full || debug_pagealloc_enabled())
+		flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
+
+	__create_pgd_mapping(init_mm.pgd, start, virt, size,
+			     PAGE_KERNEL, NULL, flags);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(populate_range_driver_managed);
+
+int depopulate_range_driver_managed(u64 start, u64 size,
+			const char *resource_name)
+{
+	if (check_range_driver_managed(start, size, resource_name))
+		return -EINVAL;
+
+	unmap_hotplug_range(start, start + size, false, NULL);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(depopulate_range_driver_managed);
+
 /*
  * This memory hotplug notifier helps prevent boot memory from being
  * inadvertently removed as it blocks pfn range offlining process in