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/20240626140330.89836-1-urezki@gmail.com
Fixes: 062eacf57ad9 ("mm: vmalloc: remove a global vmap_blocks xarray")
Reported-by: Nick Bowler <nbowler@draconx.ca>
Closes: https://lore.kernel.org/linux-kernel/ZntjIE6msJbF8zTa@MiWiFi-R3L-srv/T/
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Hailong.Liu <hailong.liu@oppo.com>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index d0cbdd7c1e5bc880cbc7d6b77b9919884a391e5f..e34ea860153f27ee8c07e1974da6c633111427d1 100644 (file)
--- a/mm/vmalloc.c
+++ b/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;
 }