Subject: Re: [PATCH RFC] arm64/vmalloc: use module region only for
 module_alloc() if CONFIG_RANDOMIZE_BASE is set
To:     Linux regressions mailing list <regressions@lists.linux.dev>,
        Ard Biesheuvel <ardb@kernel.org>
References: <20221227092634.445212-1-liushixin2@huawei.com>
 <b93ec55c-f6f0-274a-e7d6-edb419b4be8a@huawei.com>
 <20230129134147.f19ca0641f1133f3e3bc185b@linux-foundation.org>
 <20230131150644.GA2605@willie-the-truck>
 <20230131150750.GB2605@willie-the-truck>
 <CAMj1kXGaxehOcrQqFZNA+C3dTk_H8sBr_1wsN3_KN82nXVaG_g@mail.gmail.com>
 <20230207112940.GA12147@willie-the-truck>
 <8c287b1d-476c-7b00-27f6-76c3a1a5fd46@leemhuis.info>
CC:     Andrew Morton <akpm@linux-foundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Uladzislau Rezki <urezki@gmail.com>,
        Christoph Hellwig <hch@infradead.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
        Will Deacon <will@kernel.org>
From:   Liu Shixin <liushixin2@huawei.com>
Message-ID: <d56ba711-e978-81ef-def3-8c1ef8ecd7d8@huawei.com>
Date:   Tue, 28 Feb 2023 09:46:50 +0800
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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@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@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@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.
>
> .
>