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    SubjectRe: [PATCH 5.15] mm: validate buddy page before using
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    在 2022/6/20 下午8:24, Greg KH 写道:
    > On Mon, Jun 20, 2022 at 08:18:40PM +0800, Xianting Tian wrote:
    >> 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,
    > So just for 5.18? I am confused.
    Sorry, 5.18 needs the same fix with 5.15.  I will send the patch for it.
    >
    >> 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?
    > 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.
    Understood. I will send for all branches.
    >
    > greg k-h

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