subpage_register() expects "end" to be the last byte in the mapping.
Registering a non-page-aligned memory region that extends up to or
beyond a page boundary causes subpage_register() to silently fail
through the (end >= PAGE_SIZE) check.
This bug does not cause noticeable problems for mappings that do not
extend to a page boundary, though they do register an extra byte.
Signed-off-by: Tyler Hall <tylerwhall@gmail.com> Reviewed-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Avi Kivity <avi@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>