Re: [PATCH v4 09/14] xen/arm32: head: Remove restriction where to load Xen

[Luca Fancellu <Luca.Fancellu@xxxxxxx>]

> On 13 Jan 2023, at 10:11, Julien Grall <julien@xxxxxxx> wrote:
> 
> From: Julien Grall <jgrall@xxxxxxxxxx>
> 
> At the moment, bootloaders can load Xen anywhere in memory but the
> region 2MB - 4MB. While I am not aware of any issue, we have no way
> to tell the bootloader to avoid that region.
> 
> In addition to that, in the future, Xen may grow over 2MB if we
> enable feature like UBSAN or GCOV. To avoid widening the restriction
> on the load address, it would be better to get rid of it.
> 
> When the identity mapping is clashing with the Xen runtime mapping,
> we need an extra indirection to be able to replace the identity
> mapping with the Xen runtime mapping.
> 
> Reserve a new memory region that will be used to temporarily map Xen.
> For convenience, the new area is re-using the same first slot as the
> domheap which is used for per-cpu temporary mapping after a CPU has
> booted.
> 
> Furthermore, directly map boot_second (which cover Xen and more)
> to the temporary area. This will avoid to allocate an extra page-table
> for the second-level and will helpful for follow-up patches (we will
> want to use the fixmap whilst in the temporary mapping).
> 
> Lastly, some part of the code now needs to know whether the temporary
> mapping was created. So reserve r12 to store this information.
> 
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
> ----
> 

Hi Julien,

> 
> +/*
> + * Remove the temporary mapping of Xen starting at TEMPORARY_XEN_VIRT_START.
> + *
> + * Clobbers r0 - r1

NIT: r0 - r3?

> + */
> +remove_temporary_mapping:
> +        /* r2:r3 := invalid page-table entry */
> +        mov   r2, #0
> +        mov   r3, #0
> +
> +        adr_l r0, boot_pgtable
> +        mov_w r1, TEMPORARY_XEN_VIRT_START
> +        get_table_slot r1, r1, 1     /* r1 := first slot */
> +        lsl   r1, r1, #3             /* r1 := first slot offset */
> +        strd  r2, r3, [r0, r1]
> +
> +        flush_xen_tlb_local r0
> +
> +        mov  pc, lr
> +ENDPROC(remove_temporary_mapping)
> +

The rest looks good to me, I’ve also built for arm64/32 and test this patch on 
fvp aarch32 mode,
booting Dom0 and creating/running/destroying some guests.

Reviewed-by: Luca Fancellu <luca.fancellu@xxxxxxx>
Tested-by: Luca Fancellu <luca.fancellu@xxxxxxx>

Cheers,
Luca