bootmem: fix aligning of node-relative indexes and offsets

Absolute alignment requirements may never be applied to node-relative
offsets.  Andreas Herrmann spotted this flaw when a bootmem allocation on
an unaligned node was itself not aligned because the combination of an
unaligned node with an aligned offset into that node is not garuanteed to
be aligned itself.

This patch introduces two helper functions that align a node-relative
index or offset with respect to the node's starting address so that the
absolute PFN or virtual address that results from combining the two
satisfies the requested alignment.

Then all the broken ALIGN()s in alloc_bootmem_core() are replaced by these
helpers.

Signed-off-by: Johannes Weiner <[email protected]>
Reported-by: Andreas Herrmann <[email protected]>
Debugged-by: Andreas Herrmann <[email protected]>
Reviewed-by: Andreas Herrmann <[email protected]>
Tested-by: Andreas Herrmann <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/bootmem.c

@@ -405,6 +405,29 @@ int __init reserve_bootmem(unsigned long addr, unsigned long size,
 }
 #endif /* !CONFIG_HAVE_ARCH_BOOTMEM_NODE */
 
+static unsigned long align_idx(struct bootmem_data *bdata, unsigned long idx,
+			unsigned long step)
+{
+	unsigned long base = bdata->node_min_pfn;
+
+	/*
+	 * Align the index with respect to the node start so that the
+	 * combination of both satisfies the requested alignment.
+	 */
+
+	return ALIGN(base + idx, step) - base;
+}
+
+static unsigned long align_off(struct bootmem_data *bdata, unsigned long off,
+			unsigned long align)
+{
+	unsigned long base = PFN_PHYS(bdata->node_min_pfn);
+
+	/* Same as align_idx for byte offsets */
+
+	return ALIGN(base + off, align) - base;
+}
+
 static void * __init alloc_bootmem_core(struct bootmem_data *bdata,
 				unsigned long size, unsigned long align,
 				unsigned long goal, unsigned long limit)
@@ -441,7 +464,7 @@ static void * __init alloc_bootmem_core(struct bootmem_data *bdata,
 	else
 		start = ALIGN(min, step);
 
-	sidx = start - bdata->node_min_pfn;;
+	sidx = start - bdata->node_min_pfn;
 	midx = max - bdata->node_min_pfn;
 
 	if (bdata->hint_idx > sidx) {
@@ -450,7 +473,7 @@ static void * __init alloc_bootmem_core(struct bootmem_data *bdata,
 		 * catch the fallback below.
 		 */
 		fallback = sidx + 1;
-		sidx = ALIGN(bdata->hint_idx, step);
+		sidx = align_idx(bdata, bdata->hint_idx, step);
 	}
 
 	while (1) {
@@ -459,23 +482,23 @@ static void * __init alloc_bootmem_core(struct bootmem_data *bdata,
 		unsigned long eidx, i, start_off, end_off;
 find_block:
 		sidx = find_next_zero_bit(bdata->node_bootmem_map, midx, sidx);
-		sidx = ALIGN(sidx, step);
+		sidx = align_idx(bdata, sidx, step);
 		eidx = sidx + PFN_UP(size);
 
 		if (sidx >= midx || eidx > midx)
 			break;
 
 		for (i = sidx; i < eidx; i++)
 			if (test_bit(i, bdata->node_bootmem_map)) {
-				sidx = ALIGN(i, step);
+				sidx = align_idx(bdata, i, step);
 				if (sidx == i)
 					sidx += step;
 				goto find_block;
 			}
 
 		if (bdata->last_end_off & (PAGE_SIZE - 1) &&
 				PFN_DOWN(bdata->last_end_off) + 1 == sidx)
-			start_off = ALIGN(bdata->last_end_off, align);
+			start_off = align_off(bdata, bdata->last_end_off, align);
 		else
 			start_off = PFN_PHYS(sidx);
 
@@ -499,7 +522,7 @@ static void * __init alloc_bootmem_core(struct bootmem_data *bdata,
 	}
 
 	if (fallback) {
-		sidx = ALIGN(fallback - 1, step);
+		sidx = align_idx(bdata, fallback - 1, step);
 		fallback = 0;
 		goto find_block;
 	}