The physical page which we clear is accessed via additional temp kernel
mapping for the period of zeroing operation. However in systems with virtual
d-cache (most ARMs) when write-allocate feature is enabled, we can have
modified but unflushed content pertaining to this physical page still in the
d-cache due to its primary (pre-existing) mapping. In such scenario that
cached content upon flush is likely to overwrite [portions of] the physical
page we want to zero here..
This is a general problem with multiple virtual mappings covering the same
physical page with write-allocate and virtual d-cache: there is inherent
potential for corruptions of this kind, which are not easily resolved; it is
best policy that such multiple mappings be not allowed.
Obtained from: Marvell, Semihalf
e725b1fa27