arm64: Add memory hotplug support

Wire up the basic support for hot-adding memory. Since memory hotplug
is fairly tightly coupled to sparsemem, we tweak pfn_valid() to also
cross-check the presence of a section in the manner of the generic
implementation, before falling back to memblock to check for no-map
regions within a present section as before. By having arch_add_memory(()
create the linear mapping first, this then makes everything work in the
way that __add_section() expects.

We expect hotplug to be ACPI-driven, so the swapper_pg_dir updates
should be safe from races by virtue of the global device hotplug lock.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 674c409a8ce4..da513a1facf4 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1046,3 +1046,20 @@ int pud_free_pmd_page(pud_t *pudp, unsigned long addr)
 	pmd_free(NULL, table);
 	return 1;
 }
+
+#ifdef CONFIG_MEMORY_HOTPLUG
+int arch_add_memory(int nid, u64 start, u64 size, struct vmem_altmap *altmap,
+		    bool want_memblock)
+{
+	int flags = 0;
+
+	if (rodata_full || debug_pagealloc_enabled())
+		flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
+
+	__create_pgd_mapping(swapper_pg_dir, start, __phys_to_virt(start),
+			     size, PAGE_KERNEL, pgd_pgtable_alloc, flags);
+
+	return __add_pages(nid, start >> PAGE_SHIFT, size >> PAGE_SHIFT,
+			   altmap, want_memblock);
+}
+#endif