x86/numa: Fix the sort compare func used in numa_fill_memblks()

[ Upstream commit b626070 ]

The compare function used to sort memblks into starting address
order fails when the result of its u64 address subtraction gets
truncated to an int upon return.

The impact of the bad sort is that memblks will be filled out
incorrectly. Depending on the set of memblks, a user may see no
errors at all but still have a bad fill, or see messages reporting
a node overlap that leads to numa init failure:

[] node 0 [mem: ] overlaps with node 1 [mem: ]
[] No NUMA configuration found

Replace with a comparison that can only result in: 1, 0, -1.

Fixes: 8f012db ("x86/numa: Introduce numa_fill_memblks()")
Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Link: https://lore.kernel.org/r/99dcb3ae87e04995e9f293f6158dc8fa0749a487.1705085543.git.alison.schofield@intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

arch/x86/mm/numa.c

@@ -961,7 +961,7 @@ static int __init cmp_memblk(const void *a, const void *b)
 	const struct numa_memblk *ma = *(const struct numa_memblk **)a;
 	const struct numa_memblk *mb = *(const struct numa_memblk **)b;
 
-	return ma->start - mb->start;
+	return (ma->start > mb->start) - (ma->start < mb->start);
 }
 
 static struct numa_memblk *numa_memblk_list[NR_NODE_MEMBLKS] __initdata;