linux-kernel - [PATCH] x86/NUMA: don't pass MAX_NUMNODES to memblock_set

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Date: Wed, 29 May 2024 09:42:05 +0200
From: Jan Beulich <jbeulich@...e.com>
To: lkml <linux-kernel@...r.kernel.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>,
 Andrew Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH] x86/NUMA: don't pass MAX_NUMNODES to memblock_set_node()

On an (old) x86 system with SRAT just covering space above 4Gb:

    ACPI: SRAT: Node 0 PXM 0 [mem 0x100000000-0xfffffffff] hotplug

the commit referenced below leads to this NUMA configuration no longer
being refused by a CONFIG_NUMA=y kernel (previously

    NUMA: nodes only cover 6144MB of your 8185MB e820 RAM. Not used.
    No NUMA configuration found
    Faking a node at [mem 0x0000000000000000-0x000000027fffffff]

was seen in the log directly after the message quoted above), because of
memblock_validate_numa_coverage() checking for NUMA_NO_NODE (only). This
in turn led to memblock_alloc_range_nid()'s warning about MAX_NUMNODES
triggering, followed by a NULL deref in memmap_init() when trying to
access node 64's (NODE_SHIFT=6) node data.

To compensate said change, avoid passing MAX_NUMNODES to
memblock_set_node(). In turn numa_clear_kernel_node_hotplug()'s check
then also needs adjusting.

Fixes: ff6c3d81f2e8 ("NUMA: optimize detection of memory with no node id assigned by firmware")
Signed-off-by: Jan Beulich <jbeulich@...e.com>
Cc: stable@...r.kernel.org
---
This still leaves MAX_NUMNODES uses in various other places in
mm/memblock.c. Interestingly
https://lore.kernel.org/lkml/20170309034415.GA16588@WeideMacBook-Pro.local/T/#t
was a more complete patch which, for an unclear reason, looks to never
have made it anywhere.

--- a/arch/x86/mm/numa.c
+++ b/arch/x86/mm/numa.c
@@ -493,7 +493,7 @@ static void __init numa_clear_kernel_nod
 	for_each_reserved_mem_region(mb_region) {
 		int nid = memblock_get_region_node(mb_region);
 
-		if (nid != MAX_NUMNODES)
+		if (nid != NUMA_NO_NODE)
 			node_set(nid, reserved_nodemask);
 	}
 
@@ -614,9 +614,9 @@ static int __init numa_init(int (*init_f
 	nodes_clear(node_online_map);
 	memset(&numa_meminfo, 0, sizeof(numa_meminfo));
 	WARN_ON(memblock_set_node(0, ULLONG_MAX, &memblock.memory,
-				  MAX_NUMNODES));
+				  NUMA_NO_NODE));
 	WARN_ON(memblock_set_node(0, ULLONG_MAX, &memblock.reserved,
-				  MAX_NUMNODES));
+				  NUMA_NO_NODE));
 	/* In case that parsing SRAT failed. */
 	WARN_ON(memblock_clear_hotplug(0, ULLONG_MAX));
 	numa_reset_distance();