Re: [PATCH v5 01/13] xen/arm64: head.S: Introduce enable_{boot,secondary}_cpu_mm()

[Julien Grall <julien@xxxxxxx>]

Hi Henry,

On 14/08/2023 05:25, Henry Wang wrote:
> From: Wei Chen <wei.chen@xxxxxxx>
>
> At the moment, on MMU system, enable_mmu() 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 on the boot CPU to remove all 1:1 mapping.
>
> Since remove_identity_mapping() is not necessary on Non-MMU system,
> and we also avoid creating empty function for Non-MMU system, trying
> to keep only one codeflow in arm64/head.S, we move path switch and
> remove_identity_mapping() in enable_mmu() on MMU system.
>
> As the remove_identity_mapping should only be called for the boot
> CPU only, so we introduce enable_boot_cpu_mm() for boot CPU and
> enable_secondary_cpu_mm() for secondary CPUs in this patch.
>
> Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx> > Signed-off-by: Henry Wang 
> <Henry.Wang@xxxxxxx>
One remark below. With or without it addressed:

Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>

[...]

> +/*
> + * Enable mm (turn on the data cache and the MMU) for secondary CPUs.
> + * The function will return to the virtual address provided in LR (e.g. the
> + * runtime mapping).
> + *
> + * Inputs:
> + *   lr : Virtual address to return to.
> + *
> + * Clobbers x0 - x5
> + */
> +enable_secondary_cpu_mm:
> +        mov   x5, lr
> +
> +        load_paddr x0, init_ttbr
> +        ldr   x0, [x0]
> +
> +        bl    enable_mmu
> +        mov   lr, x5
> +
> +        /* Return to the virtual address requested by the caller. */
> +        ret
> +ENDPROC(enable_secondary_cpu_mm)
NIT: enable_mmu() could directly return to the virtual address. This 
would reduce the function to:
load_paddr x0, init_ttbr
ldr   x0, [x0]

/* Return to the virtual address requested by the caller.
b enable_mmu

> +
> +/*
> + * Enable mm (turn on the data cache and the MMU) for the boot CPU.
> + * The function will return to the virtual address provided in LR (e.g. the
> + * runtime mapping).
> + *
> + * Inputs:
> + *   lr : Virtual address to return to.
> + *
> + * Clobbers x0 - x5
> + */
> +enable_boot_cpu_mm:
> +        mov   x5, lr
> +
> +        bl    create_page_tables
> +        load_paddr x0, boot_pgtable
> +
> +        bl    enable_mmu
> +
> +        /*
> +         * The MMU is turned on and we are in the 1:1 mapping. Switch
> +         * to the runtime mapping.
> +         */
> +        ldr   x0, =1f
> +        br    x0
> +1:
> +        mov   lr, x5
> +        /*
> +         * 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.
> +         * Function will return to the virtual address requested by the caller.
> +         */
> +        b     remove_identity_mapping
> +ENDPROC(enable_boot_cpu_mm)
> +
>   /*
>    * Remove the 1:1 map from the page-tables. It is not easy to keep track
>    * where the 1:1 map was mapped, so we will look for the top-level entry
Cheers,

--
Julien Grall