kvm: support using KVM_MEM_READONLY flag for regions

kvm: support using KVM_MEM_READONLY flag for regions

For readonly memory regions and rom devices in romd_mode,
we make use of the KVM_MEM_READONLY. A slot that uses
KVM_MEM_READONLY can be read from and code can execute from the
region, but writes will exit to qemu.

For rom devices with !romd_mode, we force the slot to be
removed so reads or writes to the region will exit to qemu.
(Note that a memory region in this state is not executable
within kvm.)

v7:
 * Update for readable => romd_mode rename (5f9a5ea1)

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> (v4)
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> (v5)
Message-id: 1369816047-16384-4-git-send-email-jordan.l.justen@intel.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>