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

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

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 ?

> 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