Re: [PATCH v2 04/40] xen/arm: add an option to define Xen start address for Armv8-R

[Julien Grall <julien@xxxxxxx>]

Hi,

On 18/01/2023 10:22, Wei Chen wrote:
> > > Although it is unlikely that vendors using the Armv8-R IP will do so, it
> > > is indeed an option. In the ID register, there are also related bits in
> > > ID_AA64MMFR0_EL1 (MSA_frac) to indicate this.
> > >
> > > > > ---
> > > > >     xen/arch/arm/Kconfig           |  8 ++++++++
> > > > >     xen/arch/arm/platforms/Kconfig | 16 +++++++++++++---
> > > > >     2 files changed, 21 insertions(+), 3 deletions(-)
> > > > >
> > > > > diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
> > > > > index ace7178c9a..c6b6b612d1 100644
> > > > > --- a/xen/arch/arm/Kconfig
> > > > > +++ b/xen/arch/arm/Kconfig
> > > > > @@ -145,6 +145,14 @@ config TEE
> > > > >           This option enables generic TEE mediators support. It allows
> > > > guests
> > > > >           to access real TEE via one of TEE mediators implemented in
> > XEN.
> > > > > +config XEN_START_ADDRESS
> > > > > +       hex "Xen start address: keep default to use platform defined
> > > > address"
> > > > > +       default 0
> > > > > +       depends on ARM_V8R
> > > > It is still pretty unclear to me what would be the difference between
> > > > HAS_MPU and ARM_V8R.
> > > If we don't want to support non-MPU supported Armv8-R, I think they are
> > the
> > > same. IMO, non-MPU supported Armv8-R is meaningless to Xen.
> > OOI, why do you think this is meaningless?
> If there is Armv8-R board without EL2 MPU, how can we protect Xen?
So what you call EL2 MPU is an MPU that is following the Arm 
specification. In theory, you could have a proprietary mechanism for that.
So the question is whether a system not following the Arm specification 
is allowed.
Cheers,

--
Julien Grall