Re: [PATCH v3 24/52] xen/mpu: build up start-of-day Xen MPU memory region map

[Ayan Kumar Halder <ayankuma@xxxxxxx>]

Hi Penny,

On 26/06/2023 04:34, Penny Zheng wrote:
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>
> The start-of-day Xen MPU memory region layout shall be like
> as follows:
>
> xen_mpumap[0] : Xen text
> xen_mpumap[1] : Xen read-only data
> xen_mpumap[2] : Xen read-only after init data
> xen_mpumap[3] : Xen read-write data
> xen_mpumap[4] : Xen BSS
> xen_mpumap[5] : Xen init text
> xen_mpumap[6] : Xen init data
>
> The layout shall be compliant with what we describe in xen.lds.S,
> or the codes need adjustment.
>
> Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
> Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> ---
> v3:
> - cache maintanence for safety when modifying MPU memory mapping table
> - Hardcode index for all data/text sections
> - To make sure that alternative instructions are included, use "_einitext"
> as the start of the "Init data" section.
> ---
< snip>
> +/*
> + * Static start-of-day Xen EL2 MPU memory region layout:
> + *
> + *     xen_mpumap[0] : Xen text
> + *     xen_mpumap[1] : Xen read-only data
> + *     xen_mpumap[2] : Xen read-only after init data
> + *     xen_mpumap[3] : Xen read-write data
> + *     xen_mpumap[4] : Xen BSS
> + *     xen_mpumap[5] : Xen init text
> + *     xen_mpumap[6] : Xen init data
> + *
> + * Clobbers x0 - x6
> + *
> + * It shall be compliant with what describes in xen.lds.S, or the below
> + * codes need adjustment.
> + */
> +ENTRY(prepare_early_mappings)
> +    /* x0: region sel */
> +    mov   x0, xzr
> +    /* Xen text section. */
> +    load_paddr x1, _stext
> +    load_paddr x2, _etext
> +    prepare_xen_region x0, x1, x2, x3, x4, x5, x6, attr_prbar=REGION_TEXT_PRBAR
> +
> +    add   x0, x0, #1
> +    /* Xen read-only data section. */
> +    load_paddr x1, _srodata
> +    load_paddr x2, _erodata
> +    prepare_xen_region x0, x1, x2, x3, x4, x5, x6, attr_prbar=REGION_RO_PRBAR
> +
> +    add   x0, x0, #1
> +    /* Xen read-only after init data section. */
> +    load_paddr x1, __ro_after_init_start
> +    load_paddr x2, __ro_after_init_end
> +    prepare_xen_region x0, x1, x2, x3, x4, x5, x6
> +
> +    add   x0, x0, #1
> +    /* Xen read-write data section. */
> +    load_paddr x1, __ro_after_init_end
> +    load_paddr x2, __init_begin
> +    prepare_xen_region x0, x1, x2, x3, x4, x5, x6
> +
> +    add   x0, x0, #1
> +    /* Xen BSS section. */
> +    load_paddr x1, __bss_start
> +    load_paddr x2, __bss_end
> +    prepare_xen_region x0, x1, x2, x3, x4, x5, x6
> +
> +    add   x0, x0, #1
> +    /* Xen init text section. */
> +    load_paddr x1, _sinittext
> +    load_paddr x2, _einittext
> +    prepare_xen_region x0, x1, x2, x3, x4, x5, x6, attr_prbar=REGION_TEXT_PRBAR
> +
> +    add   x0, x0, #1
> +    /* Xen init data section. */
> +    /*
> +     * Even though we are not using alternative instructions in MPU yet,
> +     * we want to use "_einitext" for the start of the "Init data" section
> +     * to make sure they are included.
> +     */
> +    load_paddr x1, _einittext
> +    roundup_section x1
> +    load_paddr x2, __init_end
> +    prepare_xen_region x0, x1, x2, x3, x4, x5, x6
> +
> +    /* Ensure any MPU memory mapping table updates made above have occurred. */
> +    dsb   nshst
> +    ret
> +ENDPROC(prepare_early_mappings)
Any reason why this is in assembly ?

We have implemented it in C 
https://github.com/Xilinx/xen/blob/d1258f1cefe406a3f91237b8106746c089864651/xen/arch/arm_mpu/mm_mpu.c#L941 
, so that it can be common between R82 and R52.
- Ayan