mm: fix wrong vmap address calculations with odd NR_CPUS values

Commit db64fe02258f ("mm: rewrite vmap layer") introduced code that does
address calculations under the assumption that VMAP_BLOCK_SIZE is a
power of two.  However, this might not be true if CONFIG_NR_CPUS is not
set to a power of two.

Wrong vmap_block index/offset values could lead to memory corruption.
However, this has never been observed in practice (or never been
diagnosed correctly); what caught this was the BUG_ON in vb_alloc() that
checks for inconsistent vmap_block indices.

To fix this, ensure that VMAP_BLOCK_SIZE always is a power of two.

Reported-by: Pavel Kysilka <>
Reported-by: Matias A. Fonzo <>
Signed-off-by: Clemens Ladisch <>
Signed-off-by: Stefan Richter <>
Cc: Nick Piggin <>
Cc: Jeremy Fitzhardinge <>
Cc: Krzysztof Helt <>
Cc: Andrew Morton <>
Cc: 2.6.28+ <>
Signed-off-by: Linus Torvalds <>
1 file changed