Re: [PATCH v2 14/40] xen/arm64: head: Jump to the runtime mapping in enable_mm()

[Julien Grall <julien@xxxxxxx>]

Hi Penny,

On 13/01/2023 05:28, Penny Zheng wrote:
> At the moment, on MMU system, enable_mm() will return to an address in
> the 1:1 mapping, then each path is responsible to switch to virtual runtime
> mapping. Then remove_identity_mapping() is called to remove all 1:1 mapping.
>
> Since remove_identity_mapping() is not necessary on MPU system, and we also
> avoid creating empty function for MPU system, trying to keep only one codeflow
> in arm64/head.S, we move path switch and remove_identity_mapping() in
> enable_mm() on MMU system.
AFAICT, remove_identity_mapping() is still using ENTRY(). But you could 
avoid to introduce ENTRY() if you re-order your series so this patch 
happens before the MMU specific code is moved in a separate helper.
> Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
> Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> ---
>   xen/arch/arm/arm64/head.S     | 28 +++++++++++++---------------
>   xen/arch/arm/arm64/head_mmu.S | 33 ++++++++++++++++++++++++++++++---
>   2 files changed, 43 insertions(+), 18 deletions(-)
This will need to be rebased on top of [1] (which will be merged pretty 
soon). There are two main differences:
 1) enable_mmu has an extra parameter to take the root page-tables
 2) the remove_identity_mapping should only be called for the boot CPU.

So I think we want to introduce two functions:
 1) enable_boot_mmu
 2) enable_runtime_mmu

You might need the same for the MPU as I would expect it would be per-CPU.

Cheers,

[1] 20230127195508.2786-1-julien@xxxxxxx

--
Julien Grall