Re: [XEN-devel] arm64: fix incorrect pa_range_info table to support 42 bit PA systems.

[Julien Grall <julien.grall@arm.com>]

Hello Feng,

On 13/05/17 01:26, Feng Kan wrote:
> The pa_range_info table contain incorrect root_order and t0sz which
> prevent 42 bit PA systems from booting dom0.

As I mentioned in the previous thread [1], this is not a bug. What you 
configure below is the stage-2 page table and not the hypervisor page-table.

It is perfectly fine to expose less IPA (Intermediate Physical Address) 
bits than the number of PA (Physical Address) bits as long as all the 
address wired are below 40 bits (assumption made by the patch who added 
this code). Does your hardware have devices/RAM above 40 bits? If so, 
then you need to mention in the commit message.

This bring another question, now you will allocate 8 pages by default 
for both DOM0 and guests. Exposing 42 bits IPA to a guest does not sound 
necessary, so we would waste memory here. How are you going to address that?

Lastly, please quote the ARM ARM when you modify the generic ARM code to 
help the reviewer checking your code.

Cheers,

[1] 
https://lists.xenproject.org/archives/html/xen-devel/2017-05/msg01254.html

>
> Signed-off-by: Feng Kan <fkan@apm.com>
> ---
>  xen/arch/arm/p2m.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> index 34d5776..cbb8675 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -1479,7 +1479,7 @@ void __init setup_virt_paging(void)
>          [0] = { 32,      32/*32*/,  0,          1 },
>          [1] = { 36,      28/*28*/,  0,          1 },
>          [2] = { 40,      24/*24*/,  1,          1 },
> -        [3] = { 42,      24/*22*/,  1,          1 },
> +        [3] = { 42,      22/*22*/,  3,          1 },
>          [4] = { 44,      20/*20*/,  0,          2 },
>          [5] = { 48,      16/*16*/,  0,          2 },
>          [6] = { 0 }, /* Invalid */
>

-- 
Julien Grall

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