Re: [PATCH 5.15] mm: validate buddy page before using

[Xianting Tian <xianting.tian@linux.alibaba.com>]

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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).

> Something went really wrong here, I'm going to drop all of these from
> the stable queues and wait for a full series of all new backports, with
> the correct upstream commit id added, and the original signed-off-by
> lines preserved.
>
> thanks,
>
> greg k-h

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