On Mon, 12 Dec 2022, Julien Grall wrote:
> From: Julien Grall <jgrall@amazon.com>
>
> At the moment, enable_mmu() will return to an address in the 1:1 mapping
> and each path is responsible to switch to the runtime mapping.
>
> In a follow-up patch, the behavior to switch to the runtime mapping
> will become more complex. So to avoid more code/comment duplication,
> move the switch in enable_mmu().
>
> Lastly, take the opportunity to replace load from literal pool with
> mov_w.
>
> Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
> ---
> Changes in v3:
> - Fix typo in the commit message
>
> Changes in v2:
> - Patch added
> ---
> xen/arch/arm/arm32/head.S | 50 +++++++++++++++++++++++----------------
> 1 file changed, 30 insertions(+), 20 deletions(-)
>
> diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
> index ce680be91be1..40c1d7502007 100644
> --- a/xen/arch/arm/arm32/head.S
> +++ b/xen/arch/arm/arm32/head.S
> @@ -167,19 +167,11 @@ past_zImage:
> bl check_cpu_mode
> bl cpu_init
> bl create_page_tables
> - bl enable_mmu
>
> - /* We are still in the 1:1 mapping. Jump to the runtime Virtual Address. */
> - mov_w r0, primary_switched
> - mov pc, r0
> + /* Address in the runtime mapping to jump to after the MMU is enabled */
> + mov_w lr, primary_switched
> + b enable_mmu
> primary_switched:
> - /*
> - * The 1:1 map may clash with other parts of the Xen virtual memory
> - * layout. As it is not used anymore, remove it completely to
> - * avoid having to worry about replacing existing mapping
> - * afterwards.
> - */
> - bl remove_identity_mapping
> bl setup_fixmap
> #ifdef CONFIG_EARLY_PRINTK
> /* Use a virtual address to access the UART. */
> @@ -223,12 +215,10 @@ GLOBAL(init_secondary)
> bl check_cpu_mode
> bl cpu_init
> bl create_page_tables
> - bl enable_mmu
>
> -
> - /* We are still in the 1:1 mapping. Jump to the runtime Virtual Address. */
> - mov_w r0, secondary_switched
> - mov pc, r0
> + /* Address in the runtime mapping to jump to after the MMU is enabled */
> + mov_w lr, secondary_switched
> + b enable_mmu
> secondary_switched:
> /*
> * Non-boot CPUs need to move on to the proper pagetables, which were
> @@ -523,9 +513,12 @@ virtphys_clash:
> ENDPROC(create_page_tables)
>
> /*
> - * Turn on the Data Cache and the MMU. The function will return on the 1:1
> - * mapping. In other word, the caller is responsible to switch to the runtime
> - * mapping.
> + * Turn on the Data Cache and the MMU. The function will return
> + * to the virtual address provided in LR (e.g. the runtime mapping).
> + *
> + * Inputs:
> + * r9 : paddr(start)
> + * lr : Virtual address to return to
> *
> * Clobbers r0 - r3
> */
> @@ -551,7 +544,24 @@ enable_mmu:
> dsb /* Flush PTE writes and finish reads */
> mcr CP32(r0, HSCTLR) /* now paging is enabled */
> isb /* Now, flush the icache */
> - mov pc, lr
> +
> + /*
> + * The MMU is turned on and we are in the 1:1 mapping. Switch
> + * to the runtime mapping.
> + */
> + mov_w r0, 1f
> + mov pc, r0
> +1:
> + /*
> + * The 1:1 map may clash with other parts of the Xen virtual memory
> + * layout. As it is not used anymore, remove it completely to
> + * avoid having to worry about replacing existing mapping
> + * afterwards.
> + *
> + * On return this will jump to the virtual address requested by
> + * the caller.
> + */
> + b remove_identity_mapping
> ENDPROC(enable_mmu)
>
> /*
> --
> 2.38.1
>