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

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

[Feng Kan]

The pa_range_info table contain incorrect root_order and t0sz which
prevent 42 bit PA systems from booting dom0.

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 */
-- 
1.8.3.1


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

[Julien Grall]

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

[Feng Kan]

On Mon, May 15, 2017 at 7:53 AM, Julien Grall <julien.grall@arm.com> 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@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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Re: [XEN-devel] arm64: fix incorrect pa_range_info table to support 42 bit PA systems.

[Julien Grall]

Hi,

On 15/05/17 18:11, Feng Kan wrote:
> On Mon, May 15, 2017 at 7:53 AM, Julien Grall <julien.grall@arm.com> 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.

Thank you for the information.

> 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

I am not totally against using 8 pages. Although a TODO will be useful 
in the code and the commit message.

Cheers,

-- 
Julien Grall

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