1 files changed, 38 insertions, 21 deletions

diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
index 4e08246acd79..4002ced3596f 100644
--- a/arch/powerpc/mm/init_64.c
+++ b/arch/powerpc/mm/init_64.c
@@ -63,38 +63,48 @@
 
 #include <mm/mmu_decl.h>
 
-phys_addr_t memstart_addr = ~0;
-EXPORT_SYMBOL_GPL(memstart_addr);
-phys_addr_t kernstart_addr;
-EXPORT_SYMBOL_GPL(kernstart_addr);
-
 #ifdef CONFIG_SPARSEMEM_VMEMMAP
 /*
- * Given an address within the vmemmap, determine the pfn of the page that
- * represents the start of the section it is within.  Note that we have to
+ * Given an address within the vmemmap, determine the page that
+ * represents the start of the subsection it is within.  Note that we have to
  * do this by hand as the proffered address may not be correctly aligned.
  * Subtraction of non-aligned pointers produces undefined results.
  */
-static unsigned long __meminit vmemmap_section_start(unsigned long page)
+static struct page * __meminit vmemmap_subsection_start(unsigned long vmemmap_addr)
 {
-	unsigned long offset = page - ((unsigned long)(vmemmap));
+	unsigned long start_pfn;
+	unsigned long offset = vmemmap_addr - ((unsigned long)(vmemmap));
 
 	/* Return the pfn of the start of the section. */
-	return (offset / sizeof(struct page)) & PAGE_SECTION_MASK;
+	start_pfn = (offset / sizeof(struct page)) & PAGE_SUBSECTION_MASK;
+	return pfn_to_page(start_pfn);
 }
 
 /*
- * Check if this vmemmap page is already initialised.  If any section
- * which overlaps this vmemmap page is initialised then this page is
- * initialised already.
+ * Since memory is added in sub-section chunks, before creating a new vmemmap
+ * mapping, the kernel should check whether there is an existing memmap mapping
+ * covering the new subsection added. This is needed because kernel can map
+ * vmemmap area using 16MB pages which will cover a memory range of 16G. Such
+ * a range covers multiple subsections (2M)
+ *
+ * If any subsection in the 16G range mapped by vmemmap is valid we consider the
+ * vmemmap populated (There is a page table entry already present). We can't do
+ * a page table lookup here because with the hash translation we don't keep
+ * vmemmap details in linux page table.
  */
-static int __meminit vmemmap_populated(unsigned long start, int page_size)
+static int __meminit vmemmap_populated(unsigned long vmemmap_addr, int vmemmap_map_size)
 {
-	unsigned long end = start + page_size;
-	start = (unsigned long)(pfn_to_page(vmemmap_section_start(start)));
+	struct page *start;
+	unsigned long vmemmap_end = vmemmap_addr + vmemmap_map_size;
+	start = vmemmap_subsection_start(vmemmap_addr);
 
-	for (; start < end; start += (PAGES_PER_SECTION * sizeof(struct page)))
-		if (pfn_valid(page_to_pfn((struct page *)start)))
+	for (; (unsigned long)start < vmemmap_end; start += PAGES_PER_SUBSECTION)
+		/*
+		 * pfn valid check here is intended to really check
+		 * whether we have any subsection already initialized
+		 * in this range.
+		 */
+		if (pfn_valid(page_to_pfn(start)))
 			return 1;
 
 	return 0;
@@ -201,6 +211,12 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 		void *p = NULL;
 		int rc;
 
+		/*
+		 * This vmemmap range is backing different subsections. If any
+		 * of that subsection is marked valid, that means we already
+		 * have initialized a page table covering this range and hence
+		 * the vmemmap range is populated.
+		 */
 		if (vmemmap_populated(start, page_size))
 			continue;
 
@@ -290,9 +306,10 @@ void __ref vmemmap_free(unsigned long start, unsigned long end,
 		struct page *page;
 
 		/*
-		 * the section has already be marked as invalid, so
-		 * vmemmap_populated() true means some other sections still
-		 * in this page, so skip it.
+		 * We have already marked the subsection we are trying to remove
+		 * invalid. So if we want to remove the vmemmap range, we
+		 * need to make sure there is no subsection marked valid
+		 * in this range.
 		 */
 		if (vmemmap_populated(start, page_size))
 			continue;