drivers/base/memory: determine and store zone for single-zone memory blocks

test_pages_in_a_zone() is just another nasty PFN walker that can easily
stumble over ZONE_DEVICE memory ranges falling into the same memory block
as ordinary system RAM: the memmap of parts of these ranges might possibly
be uninitialized.  In fact, we observed (on an older kernel) with UBSAN:

  UBSAN: Undefined behaviour in ./include/linux/mm.h:1133:50
  index 7 is out of range for type 'zone [5]'
  CPU: 121 PID: 35603 Comm: read_all Kdump: loaded Tainted: [...]
  Hardware name: Dell Inc. PowerEdge R7425/08V001, BIOS 1.12.2 11/15/2019
  Call Trace:
   dump_stack+0x9a/0xf0
   ubsan_epilogue+0x9/0x7a
   __ubsan_handle_out_of_bounds+0x13a/0x181
   test_pages_in_a_zone+0x3c4/0x500
   show_valid_zones+0x1fa/0x380
   dev_attr_show+0x43/0xb0
   sysfs_kf_seq_show+0x1c5/0x440
   seq_read+0x49d/0x1190
   vfs_read+0xff/0x300
   ksys_read+0xb8/0x170
   do_syscall_64+0xa5/0x4b0
   entry_SYSCALL_64_after_hwframe+0x6a/0xdf
  RIP: 0033:0x7f01f4439b52

We seem to stumble over a memmap that contains a garbage zone id.  While
we could try inserting pfn_to_online_page() calls, it will just make
memory offlining slower, because we use test_pages_in_a_zone() to make
sure we're offlining pages that all belong to the same zone.

Let's just get rid of this PFN walker and determine the single zone of a
memory block -- if any -- for early memory blocks during boot.  For memory
onlining, we know the single zone already.  Let's avoid any additional
memmap scanning and just rely on the zone information available during
boot.

For memory hot(un)plug, we only really care about memory blocks that:
* span a single zone (and, thereby, a single node)
* are completely System RAM (IOW, no holes, no ZONE_DEVICE)
If one of these conditions is not met, we reject memory offlining.
Hotplugged memory blocks (starting out offline), always meet both
conditions.

There are three scenarios to handle:

(1) Memory hot(un)plug

A memory block with zone == NULL cannot be offlined, corresponding to
our previous test_pages_in_a_zone() check.

After successful memory onlining/offlining, we simply set the zone
accordingly.
* Memory onlining: set the zone we just used for onlining
* Memory offlining: set zone = NULL

So a hotplugged memory block starts with zone = NULL. Once memory
onlining is done, we set the proper zone.

(2) Boot memory with !CONFIG_NUMA

We know that there is just a single pgdat, so we simply scan all zones
of that pgdat for an intersection with our memory block PFN range when
adding the memory block. If more than one zone intersects (e.g., DMA and
DMA32 on x86 for the first memory block) we set zone = NULL and
consequently mimic what test_pages_in_a_zone() used to do.

(3) Boot memory with CONFIG_NUMA

At the point in time we create the memory block devices during boot, we
don't know yet which nodes *actually* span a memory block. While we could
scan all zones of all nodes for intersections, overlapping nodes complicate
the situation and scanning all nodes is possibly expensive. But that
problem has already been solved by the code that sets the node of a memory
block and creates the link in the sysfs --
do_register_memory_block_under_node().

So, we hook into the code that sets the node id for a memory block. If
we already have a different node id set for the memory block, we know
that multiple nodes *actually* have PFNs falling into our memory block:
we set zone = NULL and consequently mimic what test_pages_in_a_zone() used
to do. If there is no node id set, we do the same as (2) for the given
node.

Note that the call order in driver_init() is:
-> memory_dev_init(): create memory block devices
-> node_dev_init(): link memory block devices to the node and set the
		    node id

So in summary, we detect if there is a single zone responsible for this
memory block and we consequently store the zone in that case in the
memory block, updating it during memory onlining/offlining.

Link: https://lkml.kernel.org/r/20220210184359.235565-3-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reported-by: Rafael Parra <rparrazo@redhat.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Rafael Parra <rparrazo@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 96 insertions, 5 deletions

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 6ee2181adc3feb..f75e3467cb59b2 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -215,6 +215,7 @@ static int memory_block_online(struct memory_block *mem)
 		adjust_present_page_count(pfn_to_page(start_pfn), mem->group,
 					  nr_vmemmap_pages);
 
+	mem->zone = zone;
 	return ret;
 }
 
@@ -225,6 +226,9 @@ static int memory_block_offline(struct memory_block *mem)
 	unsigned long nr_vmemmap_pages = mem->nr_vmemmap_pages;
 	int ret;
 
+	if (!mem->zone)
+		return -EINVAL;
+
 	/*
 	 * Unaccount before offlining, such that unpopulated zone and kthreads
 	 * can properly be torn down in offline_pages().
@@ -234,7 +238,7 @@ static int memory_block_offline(struct memory_block *mem)
 					  -nr_vmemmap_pages);
 
 	ret = offline_pages(start_pfn + nr_vmemmap_pages,
-			    nr_pages - nr_vmemmap_pages, mem->group);
+			    nr_pages - nr_vmemmap_pages, mem->zone, mem->group);
 	if (ret) {
 		/* offline_pages() failed. Account back. */
 		if (nr_vmemmap_pages)
@@ -246,6 +250,7 @@ static int memory_block_offline(struct memory_block *mem)
 	if (nr_vmemmap_pages)
 		mhp_deinit_memmap_on_memory(start_pfn, nr_vmemmap_pages);
 
+	mem->zone = NULL;
 	return ret;
 }
 
@@ -411,11 +416,10 @@ static ssize_t valid_zones_show(struct device *dev,
 	 */
 	if (mem->state == MEM_ONLINE) {
 		/*
-		 * The block contains more than one zone can not be offlined.
-		 * This can happen e.g. for ZONE_DMA and ZONE_DMA32
+		 * If !mem->zone, the memory block spans multiple zones and
+		 * cannot get offlined.
 		 */
-		default_zone = test_pages_in_a_zone(start_pfn,
-						    start_pfn + nr_pages);
+		default_zone = mem->zone;
 		if (!default_zone)
 			return sysfs_emit(buf, "%s\n", "none");
 		len += sysfs_emit_at(buf, len, "%s", default_zone->name);
@@ -643,6 +647,82 @@ int register_memory(struct memory_block *memory)
 	return ret;
 }
 
+static struct zone *early_node_zone_for_memory_block(struct memory_block *mem,
+						     int nid)
+{
+	const unsigned long start_pfn = section_nr_to_pfn(mem->start_section_nr);
+	const unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block;
+	struct zone *zone, *matching_zone = NULL;
+	pg_data_t *pgdat = NODE_DATA(nid);
+	int i;
+
+	/*
+	 * This logic only works for early memory, when the applicable zones
+	 * already span the memory block. We don't expect overlapping zones on
+	 * a single node for early memory. So if we're told that some PFNs
+	 * of a node fall into this memory block, we can assume that all node
+	 * zones that intersect with the memory block are actually applicable.
+	 * No need to look at the memmap.
+	 */
+	for (i = 0; i < MAX_NR_ZONES; i++) {
+		zone = pgdat->node_zones + i;
+		if (!populated_zone(zone))
+			continue;
+		if (!zone_intersects(zone, start_pfn, nr_pages))
+			continue;
+		if (!matching_zone) {
+			matching_zone = zone;
+			continue;
+		}
+		/* Spans multiple zones ... */
+		matching_zone = NULL;
+		break;
+	}
+	return matching_zone;
+}
+
+#ifdef CONFIG_NUMA
+/**
+ * memory_block_add_nid() - Indicate that system RAM falling into this memory
+ *			    block device (partially) belongs to the given node.
+ * @mem: The memory block device.
+ * @nid: The node id.
+ * @context: The memory initialization context.
+ *
+ * Indicate that system RAM falling into this memory block (partially) belongs
+ * to the given node. If the context indicates ("early") that we are adding the
+ * node during node device subsystem initialization, this will also properly
+ * set/adjust mem->zone based on the zone ranges of the given node.
+ */
+void memory_block_add_nid(struct memory_block *mem, int nid,
+			  enum meminit_context context)
+{
+	if (context == MEMINIT_EARLY && mem->nid != nid) {
+		/*
+		 * For early memory we have to determine the zone when setting
+		 * the node id and handle multiple nodes spanning a single
+		 * memory block by indicate via zone == NULL that we're not
+		 * dealing with a single zone. So if we're setting the node id
+		 * the first time, determine if there is a single zone. If we're
+		 * setting the node id a second time to a different node,
+		 * invalidate the single detected zone.
+		 */
+		if (mem->nid == NUMA_NO_NODE)
+			mem->zone = early_node_zone_for_memory_block(mem, nid);
+		else
+			mem->zone = NULL;
+	}
+
+	/*
+	 * If this memory block spans multiple nodes, we only indicate
+	 * the last processed node. If we span multiple nodes (not applicable
+	 * to hotplugged memory), zone == NULL will prohibit memory offlining
+	 * and consequently unplug.
+	 */
+	mem->nid = nid;
+}
+#endif
+
 static int init_memory_block(unsigned long block_id, unsigned long state,
 			     unsigned long nr_vmemmap_pages,
 			     struct memory_group *group)
@@ -665,6 +745,17 @@ static int init_memory_block(unsigned long block_id, unsigned long state,
 	mem->nr_vmemmap_pages = nr_vmemmap_pages;
 	INIT_LIST_HEAD(&mem->group_next);
 
+#ifndef CONFIG_NUMA
+	if (state == MEM_ONLINE)
+		/*
+		 * MEM_ONLINE at this point implies early memory. With NUMA,
+		 * we'll determine the zone when setting the node id via
+		 * memory_block_add_nid(). Memory hotplug updated the zone
+		 * manually when memory onlining/offlining succeeds.
+		 */
+		mem->zone = early_node_zone_for_memory_block(mem, NUMA_NO_NODE);
+#endif /* CONFIG_NUMA */
+
 	ret = register_memory(mem);
 	if (ret)
 		return ret;