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

Mon Feb 27 09:17:18 PST 2023

On 27.02.23 17:14, 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.

Great, many thx.

>> 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?

https://docs.kernel.org/process/handling-regressions.html

Side note: that also mentions use of the "Link" tag. If the patch had
one, I'd noticed it and wouldn't bothered anyone here.

> 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.

I do that sometimes, but fwiw, from what I can see it wasn't a reporter
that was unresponsive:

https://lore.kernel.org/linux-arm-kernel/c1ff5cae-7f56-7fdb-c832-ffbcc177535b@leemhuis.info/

But I might be missing something, sorry if I do. And there was the
festive season what complicated everything. Whatever, as long as this
this is fixed.

/me wonders if we should ask "chenxiang (M)" to test that patch, too;
but /me is not even totally sure it's the same problem

>> 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)

Maybe I found the wrong words, sorry.

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
--
Everything you wanna know about Linux kernel regression tracking:
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