Re: [PATCH v4 2/2] xen/arm: Enlarge identity map space to 10TB

[Luca Fancellu <Luca.Fancellu@xxxxxxx>]

> On 16 Oct 2023, at 15:00, Bertrand Marquis <Bertrand.Marquis@xxxxxxx> wrote:
> 
> Hi
> 
> +Luca and Rahul
> 
>> On 16 Oct 2023, at 15:54, Julien Grall <julien@xxxxxxx> wrote:
>> 
>> 
>> 
>> On 16/10/2023 09:44, Michal Orzel wrote:
>>> Hi,
>> 
>> Hi,
>> 
>>> On 13/10/2023 14:26, Leo Yan wrote:
>>>> 
>>>> 
>>>> On ADLink AVA platform (Ampere Altra SoC with 32 Arm Neoverse N1 cores),
>>>> the physical memory regions are:
>>>> 
>>>>  DRAM memory regions:
>>>>    Node[0] Region[0]: 0x000080000000 - 0x0000ffffffff
>>>>    Node[0] Region[1]: 0x080000000000 - 0x08007fffffff
>>>>    Node[0] Region[2]: 0x080100000000 - 0x0807ffffffff
>>>> 
>>>> The UEFI loads Xen hypervisor and DTB into the high memory, the kernel
>>>> and ramdisk images are loaded into the low memory space:
>>>> 
>>>>  (XEN) MODULE[0]: 00000807f6df0000 - 00000807f6f3e000 Xen
>>>>  (XEN) MODULE[1]: 00000807f8054000 - 00000807f8056000 Device Tree
>>>>  (XEN) MODULE[2]: 00000000fa834000 - 00000000fc5de1d5 Ramdisk
>>>>  (XEN) MODULE[3]: 00000000fc5df000 - 00000000ffb3f810 Kernel
>>>> 
>>>> In this case, the Xen binary is loaded above 8TB, which exceeds the
>>>> maximum supported identity map space of 2TB in Xen. Consequently, the
>>>> system fails to boot.
>>>> 
>>>> This patch enlarges identity map space to 10TB, allowing module loading
>>>> within the range of [0x0 .. 0x000009ff_ffff_ffff].
>>>> 
>>>> Fixes: 1c78d76b67 ("xen/arm64: mm: Introduce helpers to 
>>>> prepare/enable/disable")
>>> I don't think a fixes tag applies here given that 2TB was just a number we 
>>> believed is enough
>>> and all of this is platform dependent.
>>> This can be dropped on commit if committer agrees
>> Xen may have booted on that platform before hand. So this would be 
>> considered a regression and therefore a tag would be warrant.
>> 
>> AFAICT, the commit is only present on the upcoming 4.18. So the question is 
>> whether Xen 4.17 booted out-of-the-box on ADLink? If the answer is yes, then 
>> we need to add a Fixes tag. But the correct one would be
>> 
> 
> @Rahul or Luca: could you give an answer here ?
> I know you used Xen on an AVA platform but was it booting out of the box ?

I can’t say for Xen 4.17, but our nightly job has run successfully on AVA for 
the commit 730406ab81094115d9fb5ca00ba8d53cec1279b3
(docs/misra: add deviations.rst to document additional deviations.)

We are not applying any patch for it to run on AVA.

> 
>> 1c78d76b67e1 ("xen/arm64: mm: Introduce helpers to prepare/enable/disable 
>> the identity mapping").
>> 
>> We would also need to consider it as a candidate for Xen 4.18 because we 
>> would regress boot on ADLink.
> 
> Ack
> 
> Cheers
> Bertrand
> 
>> 
>> Cheers,
>> 
>> --
>> Julien Grall
> 
>