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From:   Zi Yan <ziy@nvidia.com>
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     Xianting Tian <xianting.tian@linux.alibaba.com>,
        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 08:45:13 -0400
Message-ID: <3371C275-E45D-445F-838E-D43C60BCD750@nvidia.com>
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On 20 Jun 2022, at 8:24, Greg KH wrote:

> On Mon, Jun 20, 2022 at 08:18:40PM +0800, 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 chec=
k its migratetype.")
>>>>>>>> fixes a bug in 1dd214b8f21c and there is a similar bug in d9dddb=
f55667 that
>>>>>>>> can be fixed in a similar way too.
>>>>>>>>
>>>>>>>> In unset_migratetype_isolate(), we also need the fix, so move pa=
ge_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 =
get 0 pfn or
>>>>>>>> less than the pfn_base value. We need page_is_buddy() to verify =
the buddy to
>>>>>>>> prevent accessing an invalid buddy.
>>>>>>>>
>>>>>>>> Fixes: d9dddbf55667 ("mm/page_alloc: prevent merging between iso=
lated 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 i=
ts 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 che=
ck during pageblock merge check.
>>>>>>
>>>>>>   =C2=A0=C2=A0=C2=A0 Fixes: 1dd214b8f21c ("mm: page_alloc: avoid m=
erging non-fallbackable
>>>>>> pageblocks with others")
>>>>>>   =C2=A0=C2=A0=C2=A0 Link:
>>>>>> https://lore.kernel.org/all/20220330154208.71aca532@gandalf.local.=
home/
>>>>>>   =C2=A0=C2=A0=C2=A0 Reported-and-tested-by: Steven Rostedt <roste=
dt@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 =
the
>>>>> subject lines changed?
>>>> Yes, the changes of 5.15 are not same with others branches, because =
we need
>>>> additional fix for 5.15,
>>>>
>>>> You can check it in the thread:
>>>>
>>>> https://lore.kernel.org/linux-mm/435B45C3-E6A5-43B2-A5A2-318C748691F=
C@nvidia.com/ <https://lore.kernel.org/linux-mm/435B45C3-E6A5-43B2-A5A2-3=
18C748691FC@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 a=
ll
>>> 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,
>
> So just for 5.18?  I am confused.
>
>> 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?
>
> No, please send fixed up patches for all branches you want them applied=

> to as I do not understand what to do here at all, sorry.

Hi Greg,

The fixes sent by Xianting do not exist in Linus=E2=80=99s tree, since th=
e bug is
fixed by another commit, which was not intended to fix the bug from the c=
ommit
d9dddbf55667. These fixes only target the stable branches.

--
Best Regards,
Yan, Zi

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