Test smem_start before looking up pages from its value. Return
NULL if it is unset. This will result in a SIGBUS signal.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240419083331.7761-6-tzimmermann@suse.de