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From:   Zi Yan <ziy@nvidia.com>
To:     Xianting Tian <xianting.tian@linux.alibaba.com>
Cc:     Greg KH <gregkh@linuxfoundation.org>, akpm@linux-foundation.org,
        stable@vger.kernel.org, guoren@kernel.org,
        huanyi.xj@alibaba-inc.com, guohanjun@huawei.com,
        zjb194813@alibaba-inc.com, tianhu.hh@alibaba-inc.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 5.15] mm: validate buddy page before using
Date:   Mon, 20 Jun 2022 08:25:33 -0400
Message-ID: <2E1BD795-A6EA-4272-859B-A29DFAF6DC07@nvidia.com>
In-Reply-To: <d52e17da-a382-0028-2b16-105ab7053028@linux.alibaba.com>
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On 20 Jun 2022, at 8:18, Xianting Tian wrote:

> =E5=9C=A8 2022/6/20 =E4=B8=8B=E5=8D=888:06, Greg KH =E5=86=99=E9=81=93:=

>> On Mon, Jun 20, 2022 at 07:57:05PM +0800, Xianting Tian wrote:
>>> =E5=9C=A8 2022/6/20 =E4=B8=8B=E5=8D=887:42, Greg KH =E5=86=99=E9=81=93=
:
>>>> On Mon, Jun 20, 2022 at 06:54:44PM +0800, Xianting Tian wrote:
>>>>> =E5=9C=A8 2022/6/20 =E4=B8=8B=E5=8D=886:17, Greg KH =E5=86=99=E9=81=
=93:
>>>>>> On Fri, Jun 17, 2022 at 12:17:45AM +0800, Xianting Tian wrote:
>>>>>>> Commit 787af64d05cd ("mm: page_alloc: validate buddy before check=
 its migratetype.")
>>>>>>> fixes a bug in 1dd214b8f21c and there is a similar bug in d9dddbf=
55667 that
>>>>>>> can be fixed in a similar way too.
>>>>>>>
>>>>>>> In unset_migratetype_isolate(), we also need the fix, so move pag=
e_is_buddy()
>>>>>>> from mm/page_alloc.c to mm/internal.h
>>>>>>>
>>>>>>> In addition, for RISC-V arch the first 2MB RAM could be reserved =
for opensbi,
>>>>>>> so it would have pfn_base=3D512 and mem_map began with 512th PFN =
when
>>>>>>> CONFIG_FLATMEM=3Dy.
>>>>>>> But __find_buddy_pfn algorithm thinks the start pfn 0, it could g=
et 0 pfn or
>>>>>>> less than the pfn_base value. We need page_is_buddy() to verify t=
he buddy to
>>>>>>> prevent accessing an invalid buddy.
>>>>>>>
>>>>>>> Fixes: d9dddbf55667 ("mm/page_alloc: prevent merging between isol=
ated and other pageblocks")
>>>>>>> Cc: stable@vger.kernel.org
>>>>>>> Reported-by: zjb194813@alibaba-inc.com
>>>>>>> Reported-by: tianhu.hh@alibaba-inc.com
>>>>>>> Signed-off-by: Xianting Tian <xianting.tian@linux.alibaba.com>
>>>>>>> ---
>>>>>>>     mm/internal.h       | 34 ++++++++++++++++++++++++++++++++++
>>>>>>>     mm/page_alloc.c     | 37 +++---------------------------------=
-
>>>>>>>     mm/page_isolation.c |  3 ++-
>>>>>>>     3 files changed, 39 insertions(+), 35 deletions(-)
>>>>>> What is the commit id of this in Linus's tree?
>>>>> It is also this one=EF=BC=8C
>>>>>
>>>>> commit 787af64d05cd528aac9ad16752d11bb1c6061bb9
>>>>> Author: Zi Yan <ziy@nvidia.com>
>>>>> Date:=C2=A0=C2=A0 Wed Mar 30 15:45:43 2022 -0700
>>>>>
>>>>>   =C2=A0=C2=A0=C2=A0 mm: page_alloc: validate buddy before check it=
s migratetype.
>>>>>
>>>>>   =C2=A0=C2=A0=C2=A0 Whenever a buddy page is found, page_is_buddy(=
) should be called to
>>>>>   =C2=A0=C2=A0=C2=A0 check its validity.=C2=A0 Add the missing chec=
k during pageblock merge check.
>>>>>
>>>>>   =C2=A0=C2=A0=C2=A0 Fixes: 1dd214b8f21c ("mm: page_alloc: avoid me=
rging non-fallbackable
>>>>> pageblocks with others")
>>>>>   =C2=A0=C2=A0=C2=A0 Link:
>>>>> https://lore.kernel.org/all/20220330154208.71aca532@gandalf.local.h=
ome/
>>>>>   =C2=A0=C2=A0=C2=A0 Reported-and-tested-by: Steven Rostedt <rosted=
t@goodmis.org>
>>>>>   =C2=A0=C2=A0=C2=A0 Signed-off-by: Zi Yan <ziy@nvidia.com>
>>>>>   =C2=A0=C2=A0=C2=A0 Signed-off-by: Linus Torvalds <torvalds@linux-=
foundation.org>
>>>> This commit looks nothing like what you posted here.
>>>>
>>>> Why the vast difference with no explaination as to why these are so
>>>> different from the other backports you provided here?  Also why is t=
he
>>>> subject lines changed?
>>> Yes, the changes of 5.15 are not same with others branches, because w=
e need
>>> additional fix for 5.15,
>>>
>>> You can check it in the thread:
>>>
>>> https://lore.kernel.org/linux-mm/435B45C3-E6A5-43B2-A5A2-318C748691FC=
@nvidia.com/ <https://lore.kernel.org/linux-mm/435B45C3-E6A5-43B2-A5A2-31=
8C748691FC@nvidia.com/>
>>>
>>> Right. But pfn_valid_within() was removed since 5.15. So your fix is
>>> required for kernels between 5.15 and 5.17 (inclusive).
>> What is "your fix" here?
>>
>> This change differs a lot from what is in Linus's tree now, so this al=
l
>> needs to be resend and fixed up as I mention above if we are going to =
be
>> able to take this.  As-is, it's all not correct so are dropped.
>
> I think, for branches except 5.15,=C2=A0 you can just backport Zi Yan's=
 commit 787af64d05cd in Linus tree. I won't send more patches further,

Please do not back port my commit 787af64d05cd directly, because although=

it fixes the issue, the code indentation is not right. At least, I tried
to cherry-pick the commit and failed. The commit just happens to fix
the issue in commit d9dddbf55667.

>
> For 5.15, because it need additional fix except commit 787af64d05cd,=C2=
=A0 I will send a new patch as your comments.
>
> Is it ok for you?
>
>>
>> thanks,
>>
>> greg k-h

--
Best Regards,
Yan, Zi

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