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authorDavid Hildenbrand <david@redhat.com>2022-03-22 14:47:31 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2022-03-22 15:57:10 -0700
commit395f6081bad49f9c54abafebab49ee23aa985bbd (patch)
treed0b5d2953a5be44e95f46430ba29d578df310711 /mm/memory_hotplug.c
parentcc6515591b25f08ce199e9379844a964f52a27f2 (diff)
downloadlwn-395f6081bad49f9c54abafebab49ee23aa985bbd.tar.gz
lwn-395f6081bad49f9c54abafebab49ee23aa985bbd.zip
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>
Diffstat (limited to 'mm/memory_hotplug.c')
-rw-r--r--mm/memory_hotplug.c50
1 files changed, 10 insertions, 40 deletions
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index ed1a5dac6797..aee69281dad6 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1549,38 +1549,6 @@ bool mhp_range_allowed(u64 start, u64 size, bool need_mapping)
#ifdef CONFIG_MEMORY_HOTREMOVE
/*
- * Confirm all pages in a range [start, end) belong to the same zone (skipping
- * memory holes). When true, return the zone.
- */
-struct zone *test_pages_in_a_zone(unsigned long start_pfn,
- unsigned long end_pfn)
-{
- unsigned long pfn, sec_end_pfn;
- struct zone *zone = NULL;
- struct page *page;
-
- for (pfn = start_pfn, sec_end_pfn = SECTION_ALIGN_UP(start_pfn + 1);
- pfn < end_pfn;
- pfn = sec_end_pfn, sec_end_pfn += PAGES_PER_SECTION) {
- /* Make sure the memory section is present first */
- if (!present_section_nr(pfn_to_section_nr(pfn)))
- continue;
- for (; pfn < sec_end_pfn && pfn < end_pfn;
- pfn += MAX_ORDER_NR_PAGES) {
- /* Check if we got outside of the zone */
- if (zone && !zone_spans_pfn(zone, pfn))
- return NULL;
- page = pfn_to_page(pfn);
- if (zone && page_zone(page) != zone)
- return NULL;
- zone = page_zone(page);
- }
- }
-
- return zone;
-}
-
-/*
* Scan pfn range [start,end) to find movable/migratable pages (LRU pages,
* non-lru movable pages and hugepages). Will skip over most unmovable
* pages (esp., pages that can be skipped when offlining), but bail out on
@@ -1803,15 +1771,15 @@ static int count_system_ram_pages_cb(unsigned long start_pfn,
}
int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
- struct memory_group *group)
+ struct zone *zone, struct memory_group *group)
{
const unsigned long end_pfn = start_pfn + nr_pages;
unsigned long pfn, system_ram_pages = 0;
+ const int node = zone_to_nid(zone);
unsigned long flags;
- struct zone *zone;
struct memory_notify arg;
- int ret, node;
char *reason;
+ int ret;
/*
* {on,off}lining is constrained to full memory sections (or more
@@ -1843,15 +1811,17 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
goto failed_removal;
}
- /* This makes hotplug much easier...and readable.
- we assume this for now. .*/
- zone = test_pages_in_a_zone(start_pfn, end_pfn);
- if (!zone) {
+ /*
+ * We only support offlining of memory blocks managed by a single zone,
+ * checked by calling code. This is just a sanity check that we might
+ * want to remove in the future.
+ */
+ if (WARN_ON_ONCE(page_zone(pfn_to_page(start_pfn)) != zone ||
+ page_zone(pfn_to_page(end_pfn - 1)) != zone)) {
ret = -EINVAL;
reason = "multizone range";
goto failed_removal;
}
- node = zone_to_nid(zone);
/*
* Disable pcplists so that page isolation cannot race with freeing