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

[Liu Shixin]

On 2023/2/1 0:03, Ard Biesheuvel wrote:
> On Tue, 31 Jan 2023 at 16:07, Will Deacon <will at kernel.org> wrote:
>> Now really adding Ard...
>>
>> On Tue, Jan 31, 2023 at 03:06:44PM +0000, Will Deacon wrote:
>>> +Ard -- full thread here:
>>>
>>> https://lore.kernel.org/all/20221227092634.445212-1-liushixin2@huawei.com/
>>>
>>> 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:
>>>>
>>>>> Hi,
>>>>>
>>>>>
>>>>> This patch seems to have been lost in the corner. Recently I've meet this problem again
>>>>>
>>>>> on v6.1, so I would like to propose this patch again.
>>>>>
>>>>>
>>>>> Thanks,
>>>>>
>>>>>
>>>>> 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.
> .
Thanks for your advice.

>