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Subject: Re: [PATCH 2/6] mm: kfence: check kfence pool size at building time
From:   Muchun Song <muchun.song@linux.dev>
In-Reply-To: <CANpmjNMVOwgc6dBnrUbGimi1oAJacwYBzRfpaZ8nqQz-ApDMXg@mail.gmail.com>
Date:   Tue, 28 Mar 2023 21:03:15 +0800
Cc:     Muchun Song <songmuchun@bytedance.com>, glider@google.com,
        dvyukov@google.com, akpm@linux-foundation.org, jannh@google.com,
        sjpark@amazon.de, kasan-dev@googlegroups.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
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Message-Id: <FD867635-75BE-4C87-857F-057BEB5530D1@linux.dev>
References: <20230328095807.7014-1-songmuchun@bytedance.com>
 <20230328095807.7014-3-songmuchun@bytedance.com>
 <CANpmjNMVOwgc6dBnrUbGimi1oAJacwYBzRfpaZ8nqQz-ApDMXg@mail.gmail.com>
To:     Marco Elver <elver@google.com>
Precedence: bulk


> On Mar 28, 2023, at 18:14, Marco Elver <elver@google.com> wrote:
>=20
> On Tue, 28 Mar 2023 at 11:58, 'Muchun Song' via kasan-dev
> <kasan-dev@googlegroups.com> wrote:
>>=20
>> Check kfence pool size at building time to expose problem ASAP.
>>=20
>> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
>> ---
>> mm/kfence/core.c | 7 +++----
>> 1 file changed, 3 insertions(+), 4 deletions(-)
>>=20
>> 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 =3D 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");
>> +
>=20
> 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.

You are right. I didn=E2=80=99t realize this.

Thanks=20

>=20
> Nack.