[081/178] x86/vmemmap: handle unpopulated sub-pmd ranges

Commit Message

Andrew Morton April 30, 2021, 5:57 a.m. UTC

From: Oscar Salvador <[e-mail]>
Subject: x86/vmemmap: handle unpopulated sub-pmd ranges

When sizeof(struct page) is not a power of 2, sections do not span a PMD
anymore and so when populating them some parts of the PMD will remain
unused.

Because of this, PMDs will be left behind when depopulating sections since
remove_pmd_table() thinks that those unused parts are still in use.

Fix this by marking the unused parts with PAGE_UNUSED, so memchr_inv()
will do the right thing and will let us free the PMD when the last user of
it is gone.

This patch is based on a similar patch by David Hildenbrand:

https://lore.kernel.org/linux-mm/[e-mail]/

[[e-mail]: go back to the ifdef version]
  Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Oscar Salvador <[e-mail]>
Reviewed-by: David Hildenbrand <[e-mail]>
Acked-by: Dave Hansen <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: "H . Peter Anvin" <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Zi Yan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 arch/x86/mm/init_64.c |   68 ++++++++++++++++++++++++++++++++--------
 1 file changed, 55 insertions(+), 13 deletions(-)

Patch

--- a/arch/x86/mm/init_64.c~x86-vmemmap-handle-unpopulated-sub-pmd-ranges
+++ a/arch/x86/mm/init_64.c
@@ -826,6 +826,51 @@  void __init paging_init(void)
 	zone_sizes_init();
 }
 
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+#define PAGE_UNUSED 0xFD
+
+/* Returns true if the PMD is completely unused and thus it can be freed */
+static bool __meminit vmemmap_pmd_is_unused(unsigned long addr, unsigned long end)
+{
+	unsigned long start = ALIGN_DOWN(addr, PMD_SIZE);
+
+	memset((void *)addr, PAGE_UNUSED, end - addr);
+
+	return !memchr_inv((void *)start, PAGE_UNUSED, PMD_SIZE);
+}
+
+static void __meminit vmemmap_use_sub_pmd(unsigned long start)
+{
+	/*
+	 * As we expect to add in the same granularity as we remove, it's
+	 * sufficient to mark only some piece used to block the memmap page from
+	 * getting removed when removing some other adjacent memmap (just in
+	 * case the first memmap never gets initialized e.g., because the memory
+	 * block never gets onlined).
+	 */
+	memset((void *)start, 0, sizeof(struct page));
+}
+
+static void __meminit vmemmap_use_new_sub_pmd(unsigned long start, unsigned long end)
+{
+	/*
+	 * Could be our memmap page is filled with PAGE_UNUSED already from a
+	 * previous remove. Make sure to reset it.
+	 */
+	vmemmap_use_sub_pmd(start);
+
+	/*
+	 * Mark with PAGE_UNUSED the unused parts of the new memmap range
+	 */
+	if (!IS_ALIGNED(start, PMD_SIZE))
+		memset((void *)start, PAGE_UNUSED,
+		        start - ALIGN_DOWN(start, PMD_SIZE));
+	if (!IS_ALIGNED(end, PMD_SIZE))
+		memset((void *)end, PAGE_UNUSED,
+		        ALIGN(end, PMD_SIZE) - end);
+}
+#endif
+
 /*
  * Memory hotplug specific functions
  */
@@ -871,8 +916,6 @@  int arch_add_memory(int nid, u64 start,
 	return add_pages(nid, start_pfn, nr_pages, params);
 }
 
-#define PAGE_INUSE 0xFD
-
 static void __meminit free_pagetable(struct page *page, int order)
 {
 	unsigned long magic;
@@ -1006,7 +1049,6 @@  remove_pmd_table(pmd_t *pmd_start, unsig
 	unsigned long next, pages = 0;
 	pte_t *pte_base;
 	pmd_t *pmd;
-	void *page_addr;
 
 	pmd = pmd_start + pmd_index(addr);
 	for (; addr < end; addr = next, pmd++) {
@@ -1026,22 +1068,16 @@  remove_pmd_table(pmd_t *pmd_start, unsig
 				pmd_clear(pmd);
 				spin_unlock(&init_mm.page_table_lock);
 				pages++;
-			} else {
-				/* If here, we are freeing vmemmap pages. */
-				memset((void *)addr, PAGE_INUSE, next - addr);
-
-				page_addr = page_address(pmd_page(*pmd));
-				if (!memchr_inv(page_addr, PAGE_INUSE,
-						PMD_SIZE)) {
+			}
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+			else if (vmemmap_pmd_is_unused(addr, next)) {
 					free_hugepage_table(pmd_page(*pmd),
 							    altmap);
-
 					spin_lock(&init_mm.page_table_lock);
 					pmd_clear(pmd);
 					spin_unlock(&init_mm.page_table_lock);
-				}
 			}
-
+#endif
 			continue;
 		}
 
@@ -1492,11 +1528,17 @@  static int __meminit vmemmap_populate_hu
 
 				addr_end = addr + PMD_SIZE;
 				p_end = p + PMD_SIZE;
+
+				if (!IS_ALIGNED(addr, PMD_SIZE) ||
+				    !IS_ALIGNED(next, PMD_SIZE))
+					vmemmap_use_new_sub_pmd(addr, next);
+
 				continue;
 			} else if (altmap)
 				return -ENOMEM; /* no fallback */
 		} else if (pmd_large(*pmd)) {
 			vmemmap_verify((pte_t *)pmd, node, addr, next);
+			vmemmap_use_sub_pmd(addr);
 			continue;
 		}
 		if (vmemmap_populate_basepages(addr, next, node, NULL))