flush_dcache_page vs kunmap_local

[Matthew Wilcox]

In https://lore.kernel.org/lkml/CAHk-=wijdojzo56FzYqE5TOYw2Vws7ik3LEMGj9SPQaJJ+Z73Q@xxxxxxxxxxxxxx/
Linus offers the opinion that kunmap calls should imply a
flush_dcache_page().  Christoph added calls to flush_dcache_page()
in commit 8dad53a11f8d.  Was this "voodoo programming", or was there
a real problem being addressed?