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References: <20230328095807.7014-1-songmuchun@bytedance.com> <20230328095807.7014-3-songmuchun@bytedance.com>
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From:   Marco Elver <elver@google.com>
Date:   Tue, 28 Mar 2023 12:14:02 +0200
Message-ID: <CANpmjNMVOwgc6dBnrUbGimi1oAJacwYBzRfpaZ8nqQz-ApDMXg@mail.gmail.com>
Subject: Re: [PATCH 2/6] mm: kfence: check kfence pool size at building time
To:     Muchun Song <songmuchun@bytedance.com>
Cc:     glider@google.com, dvyukov@google.com, akpm@linux-foundation.org,
        jannh@google.com, sjpark@amazon.de, muchun.song@linux.dev,
        kasan-dev@googlegroups.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
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On Tue, 28 Mar 2023 at 11:58, 'Muchun Song' via kasan-dev
<kasan-dev@googlegroups.com> wrote:
>
> Check kfence pool size at building time to expose problem ASAP.
>
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  mm/kfence/core.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> index de62a84d4830..6781af1dfa66 100644
> --- a/mm/kfence/core.c
> +++ b/mm/kfence/core.c
> @@ -841,10 +841,9 @@ static int kfence_init_late(void)
>                 return -ENOMEM;
>         __kfence_pool = page_to_virt(pages);
>  #else
> -       if (nr_pages > MAX_ORDER_NR_PAGES) {
> -               pr_warn("KFENCE_NUM_OBJECTS too large for buddy allocator\n");
> -               return -EINVAL;
> -       }
> +       BUILD_BUG_ON_MSG(get_order(KFENCE_POOL_SIZE) > MAX_ORDER,
> +                        "CONFIG_KFENCE_NUM_OBJECTS is too large for buddy allocator");
> +

It's perfectly valid to want to use KFENCE with a very large pool that
is initialized on boot, and simply sacrifice the ability to initialize
late.

Nack.