[PATCH RFC] arm64/vmalloc: use module region only for module_alloc() if CONFIG_RANDOMIZE_BASE is set

[Liu Shixin]

On 2023/2/27 23:08, Linux regression tracking (Thorsten Leemhuis) wrote:
> [CCing the regression list, as it should be in the loop for regressions:
> https://docs.kernel.org/admin-guide/reporting-regressions.html]
>
> On 07.02.23 12:29, Will Deacon wrote:
>> On Tue, Jan 31, 2023 at 05:03:32PM +0100, Ard Biesheuvel wrote:
>>> On Tue, 31 Jan 2023 at 16:07, Will Deacon <will at kernel.org> wrote:
>>>> On Tue, Jan 31, 2023 at 03:06:44PM +0000, Will Deacon wrote:
>>>>> On Sun, Jan 29, 2023 at 01:41:47PM -0800, Andrew Morton wrote:
>>>>>> On Sun, 29 Jan 2023 10:44:31 +0800 Liu Shixin <liushixin2 at huawei.com> wrote:
>>>>>>> On 2022/12/27 17:26, Liu Shixin wrote:
>>>>>>>> After I add a 10GB pmem device, I got the following error message when
>>>>>>>> insert module:
>>>>>>>>
>>>>>>>>  insmod: vmalloc error: size 16384, vm_struct allocation failed,
>>>>>>>>  mode:0xcc0(GFP_KERNEL), nodemask=(null),cpuset=/,mems_allowed=0
>>>>>>>>
>>>>>>>> If CONFIG_RANDOMIZE_BASE is set, the module region can be located in the
>>>>>>>> vmalloc region entirely. Although module_alloc() can fall back to a 2GB
>>>>>>>> window if ARM64_MODULE_PLTS is set, the module region is still easily
>>>>>>>> exhausted because the module region is located at bottom of vmalloc region
>>>>>>>> and the vmalloc region is allocated from bottom to top.
>>>>>>>>
>>>>>>>> Skip module region if not calling from module_alloc().
>>>>>> I'll assume this is for the arm tree.
>>>>>>
>>>>>> Acked-by: Andrew Morton <akpm at linux-foundation.org>
>>>>> This looks like the same issue previously reported at:
>>>>>
>>>>> https://lore.kernel.org/all/e6a804de-a5f7-c551-ffba-e09d04e438fc@hisilicon.com/
>>>>>
>>>>> where Ard had a few suggestions but, afaict, they didn't help.
>>>>>
>>> Thanks for the cc.
>>>
>>> So this is a bit clunky, and I wonder whether we wouldn't be better
>>> off just splitting the vmalloc region into two separate regions: one
>>> for the kernel and modules, and one for everything else. That way, we
>>> lose one bit of entropy in the randomized placement, but the default
>>> 48-bit VA space is vast anway, and even on 39-bit VA configs (such as
>>> Android), I seriously doubt that we come anywhere close to exhausting
>>> the vmalloc space today.
>> That sounds like a good idea to me.
>>
>> Liu Shixin -- do you think you could have a go at implementing Ard's
>> suggestion instead?
> Liu Shixin, did you ever look into realizing this idea?
This is in my work list, but I haven't implemented it yet. Sorry for the long delay.
> Or was some progress already made and I just missed it?
>
> I'm asking, as the idea discussed afaics is not only supposed to fix the
> regression you tried to address, but also one that is now three months
> old and stalled since Mid-December -- which is really unfortunate, as
> that's not how regressions should be handled. :-/ But well, it afaik was
> caused by a patch from Ard, so it's obviously not your job to address
> it. But it seems you were working on it.
>
> Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
> --
> Everything you wanna know about Linux kernel regression tracking:
> https://linux-regtracking.leemhuis.info/about/#tldr
> If I did something stupid, please tell me, as explained on that page.
>
> .
>