Hi Henry,
On 01/08/2023 04:44, Henry Wang wrote:
There are two types of memory system architectures available for
Arm-based systems, namely the Virtual Memory System Architecture (VMSA)
and the Protected Memory System Architecture (PMSA). According to
ARM DDI 0487G.a, A VMSA provides a Memory Management Unit (MMU) that
controls address translation, access permissions, and memory attribute
determination and checking, for memory accesses made by the PE. And
refer to ARM DDI 0600A.c, the PMSA supports a unified memory protection
scheme where an Memory Protection Unit (MPU) manages instruction and
data access. Currently, Xen only suuports VMSA.
As a preparation of the Xen MPU (PMSA) support. Introduce a Kconfig
choice under the "Architecture Features" menu for user to choose the
memory system architecture for the system. Since currently only VMSA
is supported, only add the bool CONFIG_HAS_MMU to keep consistent with
the default behavior. User can choose either VMSA or PMSA but not both
in the future after PMSA/MPU is supported in Xen.
So in the long run I agree that we will want to have a choice. But this
seems to be a bit premature to introduce it now as the user can't select
the MPU and also can't deselect MMU.
Therefore, I think it would be best if we introduce an unselectable
config for now. Like:
HAS_MMU
def_bool y
This could be turned to a choice once you introduce the MPU.
Also, from my understanding, we are using the prefix HAS_ to indicate if
an architecture support the given feature. In your case, you will want
the user to select it, so I would just name the config MMU.
Cheers,
--
Julien Grall
