ia64: ensure proper NUMA distance and possible map initialization

John Paul reported a warning about bogus NUMA distance values spurred by
commit:

  620a6dc407 ("sched/topology: Make sched_init_numa() use a set for the deduplicating sort")

In this case, the afflicted machine comes up with a reported 256 possible
nodes, all of which are 0 distance away from one another.  This was
previously silently ignored, but is now caught by the aforementioned
commit.

The culprit is ia64's node_possible_map which remains unchanged from its
initialization value of NODE_MASK_ALL.  In John's case, the machine
doesn't have any SRAT nor SLIT table, but AIUI the possible map remains
untouched regardless of what ACPI tables end up being parsed.  Thus,
!online && possible nodes remain with a bogus distance of 0 (distances \in
[0, 9] are "reserved and have no meaning" as per the ACPI spec).

Follow x86 / drivers/base/arch_numa's example and set the possible map to
the parsed map, which in this case seems to be the online map.

Link: http://lore.kernel.org/r/255d6b5d-194e-eb0e-ecdd-97477a534441@physik.fu-berlin.de
Link: https://lkml.kernel.org/r/20210318130617.896309-1-valentin.schneider@arm.com
Fixes: 620a6dc407 ("sched/topology: Make sched_init_numa() use a set for the deduplicating sort")
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Reported-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Tested-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Tested-by: Sergei Trofimovich <slyfox@gentoo.org>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Anatoly Pugachev <matorola@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/ia64/kernel/acpi.c

@@ -446,7 +446,8 @@ void __init acpi_numa_fixup(void)
 	if (srat_num_cpus == 0) {
 		node_set_online(0);
 		node_cpuid[0].phys_id = hard_smp_processor_id();
-		return;
+		slit_distance(0, 0) = LOCAL_DISTANCE;
+		goto out;
 	}
 
 	/*
@@ -489,7 +490,7 @@ void __init acpi_numa_fixup(void)
 			for (j = 0; j < MAX_NUMNODES; j++)
 				slit_distance(i, j) = i == j ?
 					LOCAL_DISTANCE : REMOTE_DISTANCE;
-		return;
+		goto out;
 	}
 
 	memset(numa_slit, -1, sizeof(numa_slit));
@@ -514,6 +515,8 @@ void __init acpi_numa_fixup(void)
 		printk("\n");
 	}
 #endif
+out:
+	node_possible_map = node_online_map;
 }
 #endif				/* CONFIG_ACPI_NUMA */