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Subject: Re: [PATCH 5.15] mm: validate buddy page before using
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     akpm@linux-foundation.org, ziy@nvidia.com, 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
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 <8b16a502-5ad5-1efb-0d84-ed0a8ae63c0e@linux.alibaba.com>
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From:   Xianting Tian <xianting.tian@linux.alibaba.com>
Message-ID: <d52e17da-a382-0028-2b16-105ab7053028@linux.alibaba.com>
Date:   Mon, 20 Jun 2022 20:18:40 +0800
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在 2022/6/20 下午8:06, Greg KH 写道:
> On Mon, Jun 20, 2022 at 07:57:05PM +0800, Xianting Tian wrote:
>> 在 2022/6/20 下午7:42, Greg KH 写道:
>>> On Mon, Jun 20, 2022 at 06:54:44PM +0800, Xianting Tian wrote:
>>>> 在 2022/6/20 下午6:17, Greg KH 写道:
>>>>> 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 d9dddbf55667 that
>>>>>> can be fixed in a similar way too.
>>>>>>
>>>>>> In unset_migratetype_isolate(), we also need the fix, so move page_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=512 and mem_map began with 512th PFN when
>>>>>> CONFIG_FLATMEM=y.
>>>>>> 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 isolated 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，
>>>>
>>>> commit 787af64d05cd528aac9ad16752d11bb1c6061bb9
>>>> Author: Zi Yan <ziy@nvidia.com>
>>>> Date:   Wed Mar 30 15:45:43 2022 -0700
>>>>
>>>>       mm: page_alloc: validate buddy before check its migratetype.
>>>>
>>>>       Whenever a buddy page is found, page_is_buddy() should be called to
>>>>       check its validity.  Add the missing check during pageblock merge check.
>>>>
>>>>       Fixes: 1dd214b8f21c ("mm: page_alloc: avoid merging non-fallbackable
>>>> pageblocks with others")
>>>>       Link:
>>>> https://lore.kernel.org/all/20220330154208.71aca532@gandalf.local.home/
>>>>       Reported-and-tested-by: Steven Rostedt <rostedt@goodmis.org>
>>>>       Signed-off-by: Zi Yan <ziy@nvidia.com>
>>>>       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-A5A2-318C748691FC@nvidia.com/ <https://lore.kernel.org/linux-mm/435B45C3-E6A5-43B2-A5A2-318C748691FC@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 all
> 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,  you can just backport Zi Yan's 
commit 787af64d05cd in Linus tree. I won't send more patches further,

For 5.15, because it need additional fix except commit 787af64d05cd,  I 
will send a new patch as your comments.

Is it ok for you?

>
> thanks,
>
> greg k-h