linux-kernel - Re: [PATCH v2 2/2] kfence: Alloc kfence

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Date:   Mon, 7 Mar 2022 11:27:59 +0800
From:   Tianchen Ding <dtcccc@...ux.alibaba.com>
To:     Marco Elver <elver@...gle.com>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] kfence: Alloc kfence_pool after system startup

On 2022/3/7 10:23, Tianchen Ding wrote:
> On 2022/3/7 07:52, Marco Elver wrote:
>> On Sat, 5 Mar 2022 at 15:49, Tianchen Ding <dtcccc@...ux.alibaba.com> 
>> wrote:
>> [...]
>>> +static int kfence_init_late(void)
>>> +{
>>> +       const unsigned long nr_pages = KFENCE_POOL_SIZE / PAGE_SIZE;
>>> +       struct page *pages;
>>> +
>>> +       pages = alloc_contig_pages(nr_pages, GFP_KERNEL, 
>>> first_online_node, NULL);
>>
>>> mm/kfence/core.c:836:17: error: implicit declaration of function 
>>> ‘alloc_contig_pages’ [-Werror=implicit-function-declaration]
>>
>> This doesn't build without CMA. See ifdef CONFIG_CONTIG_ALLOC in
>> gfp.h, which declares alloc_contig_pages.
>>
>> Will alloc_pages() work as you expect? If so, perhaps only use
>> alloc_contig_pages() #ifdef CONFIG_CONTIG_ALLOC.
>>
> 
> alloc_pages() will be fine. We could free "tail" pages after inited.
> Will send v3 soon.
> 

Oh, I remember why we use alloc_contig_pages()...
alloc_pages() (or alloc_pages_exact()) only support pages less than 
MAX_ORDER (default 11). The alloc would fail when KFENCE_NUM_OBJECTS >= 512.

So the design would be:
ifndef CONFIG_CONTIG_ALLOC and KFENCE_NUM_OBJECTS exceeds MAX_ORDER, we 
do not support alloc KFENCE pool after system startup.

>> Thanks,
>> -- Marco
>