Re: [XEN v3 6/9] xen/arm: Introduce choice to enable 64/32 bit physical addressing

[Julien Grall <julien@xxxxxxx>]

Hi Stefano,

On 11/02/2023 00:34, Stefano Stabellini wrote:
> On Wed, 8 Feb 2023, Ayan Kumar Halder wrote:
> > Some Arm based hardware platforms which does not support LPAE
> > (eg Cortex-R52), uses 32 bit physical addresses.
> > Also, users may choose to use 32 bits to represent physical addresses
> > for optimization.
> >
> > To support the above use cases, we have introduced arch independent
> > configs to choose if the physical address can be represented using
> > 32 bits (PHYS_ADDR_32) or 64 bits (PHYS_ADDR_64).
> > For now only ARM_32 provides support to enable 32 bit physical
> > addressing.
> >
> > Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
> > ---
> >
> > Changes from -
> > v1 - 1. Extracted from "[XEN v1 8/9] xen/arm: Other adaptations required to support 
> > 32bit paddr".
> >
> > v2 - 1. Introduced Kconfig choice. ARM_64 can select PHYS_ADDR_64 only whereas
> > ARM_32 can select PHYS_ADDR_32 or PHYS_ADDR_64.
> > 2. For CONFIG_ARM_PA_32, paddr_t is defined as 'unsigned long'.
> >
> > (Jan,Julien please let me know if I understood your suggestion about Kconfig 
> > correctly).
> >
> >   xen/arch/Kconfig                     | 12 +++++++++++
> >   xen/arch/arm/Kconfig                 | 31 ++++++++++++++++++++++++++++
> >   xen/arch/arm/include/asm/page-bits.h |  2 ++
> >   xen/arch/arm/include/asm/types.h     |  6 ++++++
> >   4 files changed, 51 insertions(+)
> >
> > diff --git a/xen/arch/Kconfig b/xen/arch/Kconfig
> > index 7028f7b74f..1eff312b51 100644
> > --- a/xen/arch/Kconfig
> > +++ b/xen/arch/Kconfig
> > @@ -1,6 +1,18 @@
> >   config 64BIT
> >         bool
> >   
> > +config PHYS_ADDR_32
> > +       bool
> > +       help
> > +         Select this option if the physical addresses can be represented by
> > +         32 bits.
> > +
> > +config PHYS_ADDR_64
> > +       bool
> > +       help
> > +         Select this option if the physical addresses can be represented
> > +         64 bits.
> These two config symbols should be defined in xen/arch/arm/Kconfig
> (unless you plan to also define them for x86).
We discussed with Jan to consolidate types.h as RISC-V may want to use a 
32-bit paddr_t. This would mean paddr_t would be defined a common header 
and therefore those config needs to be in common.
I am not asking Ayan to work on the consolidation, but I think they 
should be defined in common (assuming arm will make use of it) and I 
would at least consider to add "select PHYS_ADDR_64" in "config X86".
Cheers,

--
Julien Grall