mm: vmalloc: check if a hash-index is in cpu_possible_mask

The problem is that there are systems where cpu_possible_mask has gaps
between set CPUs, for example SPARC.  In this scenario addr_to_vb_xa()
hash function can return an index which accesses to not-possible and not
setup CPU area using per_cpu() macro.  This results in an oops on SPARC.

A per-cpu vmap_block_queue is also used as hash table, incorrectly
assuming the cpu_possible_mask has no gaps.  Fix it by adjusting an index
to a next possible CPU.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 062eacf ("mm: vmalloc: remove a global vmap_blocks xarray")
Reported-by: Nick Bowler <[email protected]>
Closes: https://lore.kernel.org/linux-kernel/ZntjIE6msJbF8zTa@MiWiFi-R3L-srv/T/
Signed-off-by: Uladzislau Rezki (Sony) <[email protected]>
Reviewed-by: Baoquan He <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Hailong.Liu <[email protected]>
Cc: Oleksiy Avramchenko <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

mm/vmalloc.c

@@ -2543,7 +2543,15 @@ static DEFINE_PER_CPU(struct vmap_block_queue, vmap_block_queue);
 static struct xarray *
 addr_to_vb_xa(unsigned long addr)
 {
-	int index = (addr / VMAP_BLOCK_SIZE) % num_possible_cpus();
+	int index = (addr / VMAP_BLOCK_SIZE) % nr_cpu_ids;
+
+	/*
+	 * Please note, nr_cpu_ids points on a highest set
+	 * possible bit, i.e. we never invoke cpumask_next()
+	 * if an index points on it which is nr_cpu_ids - 1.
+	 */
+	if (!cpu_possible(index))
+		index = cpumask_next(index, cpu_possible_mask);
 
 	return &per_cpu(vmap_block_queue, index).vmap_blocks;
 }