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

[Feng Kan <fkan@xxxxxxx>]

On Mon, May 15, 2017 at 7:53 AM, Julien Grall <julien.grall@xxxxxxx> wrote:
> 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?
Yes,  the APM X-Gene series have all been 42 bit PA systems.
Particularly X-Gene 3, which
has its PCIe0 all the way up starting at 41 bit.

If so, then you need to
> mention in the commit message.
I will be more clear 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?
To be honest, I hadn't thought of that. I had assume system such as
these would have
plenty of memory. I will take a look regarding this. If you have any
suggestions that would
be greatly appreciated.
>
> Lastly, please quote the ARM ARM when you modify the generic ARM code to
> help the reviewer checking your code.
Thanks, will do.
>
> Cheers,
>
> [1]
> https://lists.xenproject.org/archives/html/xen-devel/2017-05/msg01254.html
>
>
>>
>> Signed-off-by: Feng Kan <fkan@xxxxxxx>
>> ---
>>  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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