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    SubjectRe: [PATCH 5.15] mm: validate buddy page before using
    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.

    > 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.

    greg k-h

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