Re: [Xen-devel] [PATCH for-4.12 v3] xen/arm: Stop relocating Xen

[Andrii Anisov <andrii.anisov@xxxxxxxxx>]

On 18.12.18 15:07, Julien Grall wrote:
> At the moment, Xen is relocated towards the end of the memory. While
> this has the advantage to free space in low memory, the code is not
> compliant with the break-before-make because it requires to switch
> between two sets of page-table. This is not entirely trivial to fix as
> it would require us to go through an identity mapping and disabling MMU.
>
> Furthermore, it looks like that some platform (such as the Hikey960)
> may not be able to bring-up secondary CPUs if the entry is too high.
>
> While Xen should be quite tiny (< 2MB), the current algorigthm to
> allocate Dom0 memory will allocate memory chunk of at least 128MB.
> Those memory chunks will always be 128MB. This means that depending on
> where the modules are loaded, an extra 128MB may disappear.
>
> As there are up to 4 modules (initramfs, XSM, kernel, DTB) loaded in
> low memory. The problem is not entirely new as you could already waste
> 512MB of low-memory. The right solution would be to fix the allocation
> algorightm. But this is independent from this patch.
>
> For user in control of the memory (such as in U-boot), all modules
> should be loaded as much as possible together or outside low-memory (i.e
> above 4GB). For other users (i.e Grub/UEFI), I believe the bootloader is
> already keeping everything together.
>
> Based on the above, it would be fine to stop relocating Xen. This has
> the advantage to simplify the code and should speed-up the boot as
> relocation is not necessary anymore.
>
> Note that the break-before-make issue is not fixed by this patch.
>
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> Reported-by: Matthew Daley <mattd@xxxxxxxxxxx>
> Tested-by: Matthew Daley <mattd@xxxxxxxxxxx>
As long as the code did not change:

Tested-by: Andrii Anisov <andrii_anisov@xxxxxxxx>
Reviewed-by: Andrii Anisov <andrii_anisov@xxxxxxxx>

--
Sincerely,
Andrii Anisov.

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