Re: [PATCH v2 2/2] xen/arm32: head Split and move MMU-specific head.S to mmu/head.S

[Julien Grall <julien@xxxxxxx>]

Hi Ayan,

On 03/11/2023 17:34, Ayan Kumar Halder wrote:
> The MMU specific code in head.S will not be used on MPU systems.
> Instead of introducing more #ifdefs which will bring complexity
> to the code, move MMU related code to mmu/head.S and keep common
> code in head.S. Two notes while moving:
>   - As "fail" in original head.S is very simple and this name is too
>     easy to be conflicted, duplicate it in mmu/head.S instead of
>     exporting it.
>   - Use ENTRY() for enable_secondary_cpu_mm, enable_boot_cpu_mm and
>     setup_fixmap as they will be used externally.
>
> Also move the assembly macros shared by head.S and mmu/head.S to
> macros.h.
>
> Note that, only the first 4KB of Xen image will be mapped as identity
> (PA == VA). At the moment, Xen guarantees this by having everything
> that needs to be used in the identity mapping in .text.header section
> of head.S, and the size will be checked by _idmap_start and _idmap_end
> at link time if this fits in 4KB. Since we are introducing a new head.S
> in this patch, although we can add .text.header to the new file to
> guarantee all identity map code still in the first 4KB. However, the
> order of these two files on this 4KB depends on the build toolchains.
> Hence, introduce a new section named .text.idmap in the region between
> _idmap_start and _idmap_end. And in Xen linker script, we force the
> .text.idmap contents to linked after .text.header. This will ensure
> code of head.S always be at the top of Xen binary.
This paragraph doesn't make much sense as you don't introduce 
.text.idmap. Instead, you piggy back on a previous commit. So I would 
suggest to delete it.
[...]

> +.macro create_mapping_entry, ptbl, virt, phys, type=PT_MEM_L3
> +        mov_w r2, XEN_PT_LPAE_ENTRY_MASK
> +        lsr   r1, \virt, #THIRD_SHIFT
> +        and   r1, r1, r2             /* r1 := slot in \tlb */
> +        lsl   r1, r1, #3             /* r1 := slot offset in \tlb */
> +
> +        lsr   r4, \phys, #THIRD_SHIFT
> +        lsl   r4, r4, #THIRD_SHIFT   /* r4 := PAGE_ALIGNED(phys) */
> +
> +        movw  r2, #\type             /* r2:r3 := right for section PT */
> +        orr   r2, r2, r4             /*          + PAGE_ALIGNED(phys) */
> +        mov   r3, #0
> +
> +        adr_l r4, \ptbl
> +
> +        strd  r2, r3, [r4, r1]
> +.endm
Newline here please.

> +.section .text.idmap, "ax", %progbits
Cheers,

--
Julien Grall