kernel: VirtBox workaround for dynamically allocated text

kernel: VirtBox workaround for dynamically allocated text

Orabug: 22377612

VirtualBox dynamically allocates space for executable text within the
kernel.  When these text addresses are encountered by stack trace back
code, they are dropped or the stack trace is terminated.

Ideally, an interface would be created so that routines could registered
to validate kernel text addresses.  Drivers like VirtualBox, would register
routines which know about dynamically allocated text.  However, this will
need more use cases from code in the mainline linux tree.

As a workaround, assume executable pages in vmalloc or module areas are
valid text addresses.  The #ifdef CONFIG_X86 is acceptable as VirtualBox
only supports x86 architecture.

Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>