[PATCH v6 5/7] drivers/base/memory: count the poison a block already holds when creating it

[Breno Leitao]

A frame flagged poisoned before memory_dev_init() runs cannot be counted
on its memory block. memblk_nr_poison_inc() divides by sections_per_block,
which memory_dev_init() sets, and the block does not exist yet. The block
is then created reading zero, however many of its frames are poisoned.

Until now nothing could poison a frame that early. It becomes possible
once a kernel flags the frames it inherits from the one that kexeced into
it, as it initializes its memmap.

memory_block_online() refuses a block that holds a poisoned frame, and a
counter stuck at zero lets one through.

Count what a block holds when it is created at boot. The walk sits behind
num_poisoned_pages, so a machine with no poison does not pay for it.

Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
---
 drivers/base/memory.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 5eead3346f1e32..77481f375c2206 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -220,11 +220,16 @@ int memory_notify(enum memory_block_state state, void *v)
 
 #if defined(CONFIG_MEMORY_FAILURE) && defined(CONFIG_MEMORY_HOTPLUG)
 static unsigned long memblk_nr_poison(struct memory_block *mem);
+static void memblk_nr_poison_init(struct memory_block *mem);
 #else
 static inline unsigned long memblk_nr_poison(struct memory_block *mem)
 {
 	return 0;
 }
+
+static inline void memblk_nr_poison_init(struct memory_block *mem)
+{
+}
 #endif
 
 /*
@@ -807,6 +812,7 @@ static int add_memory_block(unsigned long block_id, int nid, unsigned long state
 	mem->state = state;
 	mem->nid = nid;
 	INIT_LIST_HEAD(&mem->group_next);
+	memblk_nr_poison_init(mem);
 
 #ifndef CONFIG_NUMA
 	if (state == MEM_ONLINE)
@@ -1251,4 +1257,28 @@ static unsigned long memblk_nr_poison(struct memory_block *mem)
 {
 	return atomic_long_read(&mem->nr_hwpoison);
 }
+
+/*
+ * Frames poisoned before the block existed were never counted on it. Count
+ * them now, or the first unpoison takes the counter below zero.
+ */
+static void memblk_nr_poison_init(struct memory_block *mem)
+{
+	unsigned long pfn = section_nr_to_pfn(mem->start_section_nr);
+	unsigned long end = pfn + PAGES_PER_SECTION * sections_per_block;
+	unsigned long nr = 0;
+
+	/* A hotplugged block is created before its pages are online. */
+	if (mem->state != MEM_ONLINE || !atomic_long_read(&num_poisoned_pages))
+		return;
+
+	for (; pfn < end; pfn++) {
+		struct page *page = pfn_to_online_page(pfn);
+
+		if (page && PageHWPoison(page))
+			nr++;
+	}
+
+	atomic_long_set(&mem->nr_hwpoison, nr);
+}
 #endif

-- 
2.53.0-Meta