Re: [for-4.19] xen/arm64: head: only use the macro load_paddr() in the MMU code

[Julien Grall <julien@xxxxxxx>]

Hi,

On 17/10/2023 15:07, Michal Orzel wrote:
> On 17/10/2023 14:52, Julien Grall wrote:
> > The macro load_paddr() requires to know the offset between the
> > physical location of Xen and the virtual location.
> >
> > When using the MPU, x20 will always be 0. Rather than wasting
> > a register for a compile-time constant value, it would be best if
> > we can avoid using load_paddr() altogher in the common head.S code.
> s/altogher/altogether/
I will fix it.

> > The current use of load_paddr() are equivalent to adr_l() because
> > the MMU is off.
> >
> > All the use of load_paddr() in arm64/head.S are now replaced with
> > adr_l(). With that, load_paddr() can now be moved in arm64/mmu/head.S.
> >
> > For now, x20 is still unconditionally set. But this could change
> > in the future if needed.
> >
> > Signed-off-by: Julien Grall <julien@xxxxxxx>
> Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
>
> Side note:
> Looking at all the uses of load_paddr(), none of them takes place after 
> enabling MMU
> which would indicate that we actually don't need this macro at all. Do you 
> agree?
I agree they are none today called after enabling the MMU. But, 
create_table_entry() used to be called after and I can't rule out this 
will not happen again.
So I don't think we should replace the use in create_table_entry() with 
adr_l. We could consider to open-code code though.
Cheers,

--
Julien Grall