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

[Liu Shixin]

On 2023/2/28 0:14, Ard Biesheuvel wrote:
> On Mon, 27 Feb 2023 at 16:08, Linux regression tracking (Thorsten
> Leemhuis) <regressions at leemhuis.info> 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?
>>
>> Or was some progress already made and I just missed it?
>>
> This patch
>
> https://lore.kernel.org/all/20230223204101.1500373-1-ardb@kernel.org/
>
> should fix the issue.
>
>> 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. :-/
> Is it documented anywhere how regressions should be handled? The
> mailing list is flooded with hard to reproduce reports from users as
> well as automatic fuzzers and build bots, so I don't think it is
> entirely unreasonable to move unresponsive reporters to the back of
> the queue.
>
>> 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.
>>
> We are all working together here, so please refrain from telling
> people what they should or should not be working on. (I am aware that
> you probably did not mean it that way, but things tend to get lost in
> translation very easily on the mailing list)
>
> Liu, could you please check whether the linked patch addresses your issue?
Thanks, I will try this patch.
>
> Thanks,
> Ard.
> .
>