[PATCH x86/urgent 2/2] x86: Implement pfn -> nid mapping granularity check

[Tejun Heo <tj@kernel.org>]

Both SPARSEMEM and DISCONTIGMEM have limited granularity when mapping
pfn to nid.  If NUMA nodes are laid out such that the mapping cannot
be accurate, boot will fail triggering BUG_ON() in
mminit_verify_page_links().

On 32bit, it's 512MiB w/ PAE and SPARSEMEM.  This seems to have been
granular enough until commit 2706a0bf7b (x86, NUMA: Enable
CONFIG_AMD_NUMA on 32bit too).  Apparently, there is a machine which
aligns NUMA nodes to 128MiB and has only AMD NUMA but not SRAT.  As
x86_64 has granularity of 128MiB, NUMA config worked fine on the
machine; however, the commit enabled AMD NUMA config on 32bit too and
the 512MiB granularity wasn't enough.

 On node 0 totalpages: 2096615
   DMA zone: 32 pages used for memmap
   DMA zone: 0 pages reserved
   DMA zone: 3927 pages, LIFO batch:0
   Normal zone: 1740 pages used for memmap
   Normal zone: 220978 pages, LIFO batch:31
   HighMem zone: 16405 pages used for memmap
   HighMem zone: 1853533 pages, LIFO batch:31
 BUG: Int 6: CR2   (null)
      EDI   (null)  ESI 00000002  EBP 00000002  ESP c1543ecc
      EBX f2400000  EDX 00000006  ECX   (null)  EAX 00000001
      err   (null)  EIP c16209aa   CS 00000060  flg 00010002
 Stack: f2400000 00220000 f7200800 c1620613 00220000 01000000 04400000 00238000
          (null) f7200000 00000002 f7200b58 f7200800 c1620929 000375fe   (null)
        f7200b80 c16395f0 00200a02 f7200a80   (null) 000375fe 00000002   (null)
 Pid: 0, comm: swapper Not tainted 2.6.39-rc5-00181-g2706a0b #17
 Call Trace:
  [<c136b1e5>] ? early_fault+0x2e/0x2e
  [<c16209aa>] ? mminit_verify_page_links+0x12/0x42
  [<c1620613>] ? memmap_init_zone+0xaf/0x10c
  [<c1620929>] ? free_area_init_node+0x2b9/0x2e3
  [<c1607e99>] ? free_area_init_nodes+0x3f2/0x451
  [<c1601d80>] ? paging_init+0x112/0x118
  [<c15f578d>] ? setup_arch+0x791/0x82f
  [<c15f43d9>] ? start_kernel+0x6a/0x257

This patch implements node_map_pfn_alignment() which determines
maximum internode alignment and update numa_register_memblks() to
reject NUMA configuration if alignment exceeds the pfn -> nid mapping
granularity of the memory model as determined by PAGES_PER_SECTION.

This makes the problematic machine boot w/ flatmem by rejecting the
NUMA config and provides protection against crazy NUMA configurations.

Signed-off-by: Tejun Heo <tj@kernel.org>
LKML-Reference: <20110628174613.GP478@escobedo.osrc.amd.com>
Reported-and-Tested-by: Hans Rosenfeld <hans.rosenfeld@amd.com>
Cc: Conny Seidel <conny.seidel@amd.com>
---
 arch/x86/mm/numa.c |   11 ++++++++++
 include/linux/mm.h |    1 
 mm/page_alloc.c    |   54 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 66 insertions(+)

Index: work/arch/x86/mm/numa.c
===================================================================
--- work.orig/arch/x86/mm/numa.c
+++ work/arch/x86/mm/numa.c
@@ -496,6 +496,7 @@ static bool __init numa_meminfo_cover_me
 
 static int __init numa_register_memblks(struct numa_meminfo *mi)
 {
+	unsigned long pfn_align;
 	int i, nid;
 
 	/* Account for nodes with cpus and no memory */
@@ -511,6 +512,16 @@ static int __init numa_register_memblks(
 
 	/* for out of order entries */
 	sort_node_map();
+
+	/* check whether pfn -> nid mapping has enough granularity */
+	pfn_align = node_map_pfn_alignment();
+	if (pfn_align && pfn_align < PAGES_PER_SECTION) {
+		printk(KERN_WARNING "Node alignment %LuMB < min %LuMB, rejecting NUMA config\n",
+		       (u64)pfn_align << PAGE_SHIFT >> 20,
+		       (u64)PAGES_PER_SECTION << PAGE_SHIFT >> 20);
+		return -EINVAL;
+	}
+
 	if (!numa_meminfo_cover_memory(mi))
 		return -EINVAL;
 
Index: work/include/linux/mm.h
===================================================================
--- work.orig/include/linux/mm.h
+++ work/include/linux/mm.h
@@ -1313,6 +1313,7 @@ extern void remove_active_range(unsigned
 					unsigned long end_pfn);
 extern void remove_all_active_ranges(void);
 void sort_node_map(void);
+unsigned long node_map_pfn_alignment(void);
 unsigned long __absent_pages_in_range(int nid, unsigned long start_pfn,
 						unsigned long end_pfn);
 extern unsigned long absent_pages_in_range(unsigned long start_pfn,
Index: work/mm/page_alloc.c
===================================================================
--- work.orig/mm/page_alloc.c
+++ work/mm/page_alloc.c
@@ -4585,6 +4585,60 @@ void __init sort_node_map(void)
 			cmp_node_active_region, NULL);
 }
 
+/**
+ * node_map_pfn_alignment - determine the maximum internode alignment
+ *
+ * This function should be called after node map is populated and sorted.
+ * It calculates the maximum power of two alignment which can distinguish
+ * all the nodes.
+ *
+ * For example, if all nodes are 1GiB and aligned to 1GiB, the return value
+ * would indicate 1GiB alignment with (1 << (30 - PAGE_SHIFT)).  If the
+ * nodes are shifted by 256MiB, 256MiB.  Note that if only the last node is
+ * shifted, 1GiB is enough and this function will indicate so.
+ *
+ * This is used to test whether pfn -> nid mapping of the chosen memory
+ * model has fine enough granularity to avoid incorrect mapping for the
+ * populated node map.
+ *
+ * Returns the determined alignment in pfn's.  0 if there is no alignment
+ * requirement (single node).
+ */
+unsigned long __init node_map_pfn_alignment(void)
+{
+	unsigned long accl_mask = 0, last_end = 0;
+	int last_nid = -1;
+	int i;
+
+	for_each_active_range_index_in_nid(i, MAX_NUMNODES) {
+		int nid = early_node_map[i].nid;
+		unsigned long start = early_node_map[i].start_pfn;
+		unsigned long end = early_node_map[i].end_pfn;
+		unsigned long mask;
+
+		if (!start || last_nid < 0 || last_nid == nid) {
+			last_nid = nid;
+			last_end = end;
+			continue;
+		}
+
+		/*
+		 * Start with a mask granular enough to pin-point to the
+		 * start pfn and tick off bits one-by-one until it becomes
+		 * too coarse to separate the current node from the last.
+		 */
+		mask = ~((1 << __ffs(start)) - 1);
+		while (mask && last_end <= (start & (mask << 1)))
+			mask <<= 1;
+
+		/* accumulate all internode masks */
+		accl_mask |= mask;
+	}
+
+	/* convert mask to number of pages */
+	return ~accl_mask + 1;
+}
+
 /* Find the lowest pfn for a node */
 static unsigned long __init find_min_pfn_for_node(int nid)
 {