Re: [PATCH v2 1/4] xen/arm: mpu: Introduce choice between MMU and MPU

[Julien Grall <julien@xxxxxxx>]

On 23/09/2024 10:18, Ayan Kumar Halder wrote:
> On 19/09/2024 13:33, Julien Grall wrote:
> > Hi Ayan,
> Hi Julien,
> > On 18/09/2024 19:50, Ayan Kumar Halder wrote:
> > > There are features in the forthcoming patches which are dependent on
> > > MPU. For eg fixed start address.
> > > Also, some of the Xen features (eg STATIC_MEMORY) will be selected
> > > by the MPU configuration.
> > >
> > > Thus, this patch introduces a choice between MMU and MPU for the type
> > > of memory management system. By default, MMU is selected.
> > > MPU is now gated by UNSUPPORTED.
> > >
> > > Updated SUPPORT.md to state that the support for MPU is experimental.
> > >
> > > Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
> > > ---
> > > Changes from :-
> > >
> > > v1 - 1. Reworded the help messages.
> > > 2. Updated Support.md.
> > >
> > >   SUPPORT.md                     |  1 +
> > >   xen/arch/arm/Kconfig           | 16 +++++++++++++++-
> > >   xen/arch/arm/platforms/Kconfig |  2 +-
> > >   3 files changed, 17 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/SUPPORT.md b/SUPPORT.md
> > > index 23dd7e6424..3f6d788a43 100644
> > > --- a/SUPPORT.md
> > > +++ b/SUPPORT.md
> > > @@ -40,6 +40,7 @@ supported in this document.
> > >         Status, Xen in AArch64 mode: Supported
> > >       Status, Xen in AArch32 mode: Tech Preview
> > > +    Status, Xen with MPU: Experimental
> > >       Status, Cortex A57 r0p0-r1p1: Supported, not security supported
> > >       Status, Cortex A77 r0p0-r1p0: Supported, not security supported
> > >   diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
> > > index 323c967361..e881f5ba57 100644
> > > --- a/xen/arch/arm/Kconfig
> > > +++ b/xen/arch/arm/Kconfig
> > > @@ -58,10 +58,24 @@ config PADDR_BITS
> > >       default 40 if ARM_PA_BITS_40
> > >       default 48 if ARM_64
> > >   +choice
> > > +    prompt "Memory management system"
> > > +    default MMU if ARM
> > > +    help
> > > +      User can choose between the different forms of memory 
> > > management system.
> > > +
> > >   config MMU
> > > -    def_bool y
> > > +    bool "MMU"
> > >       select HAS_PMAP
> > >       select HAS_VMAP
> > > +    help
> > > +      Select it if you plan to run Xen on A-profile Armv7+
> > > +
> > > +config MPU
> > > +    bool "MPU" if UNSUPPORTED
> > > +    help
> > > +      Memory protection unit is supported on some Armv8-R systems 
> > > (UNSUPPORTED).
> > I am a bit confused with this statement. Does this mean that not all 
> > Armv8-R supports MPU? Or are you trying to say that not all of them 
> > support EL2?
> My bad. All Armv8-R system supports MPU at EL2 (as Bertrand correctly 
> pointed out). Some of them (eg R82) supports both MMU and MPU at EL1. 
> While others (eg R52) supports only MPU at EL1.
> I should rewrite it as
>
> "Memory protection unit is supported on Armv8-R systems (UNSUPPORTED)."
I think it would be more consistent with CONFIG_MMU if you write the 
following:
"Memory Protection Unit (MPU). Select if you plan to run Xen on ARMv8-R 
systems supporting EL2. (UNSUPPORTED)"
Cheers,

--
Julien Grall