From: Guo Ren <guoren@kernel.org>
To: Zi Yan <ziy@nvidia.com>
Cc: Xianting Tian <xianting.tian@linux.alibaba.com>,
Andrew Morton <akpm@linux-foundation.org>,
Vlastimil Babka <vbabka@suse.cz>, Linux-MM <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
stable@vger.kernel.org, huanyi.xj@alibaba-inc.com,
zjb194813@alibaba-inc.com, tianhu.hh@alibaba-inc.com,
Hanjun Guo <guohanjun@huawei.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Laura Abbott <labbott@redhat.com>
Subject: Re: [RESEND PATCH] mm: page_alloc: validate buddy before check the migratetype
Date: Tue, 14 Jun 2022 00:32:09 +0800 [thread overview]
Message-ID: <CAJF2gTQGXAubtas4wAzrg298dGQJntu38X48V2OzcK8xZ_vPJg@mail.gmail.com> (raw)
In-Reply-To: <0262A4FB-5A9B-47D3-8F1A-995509F56279@nvidia.com>
On Mon, Jun 13, 2022 at 11:23 PM Zi Yan <ziy@nvidia.com> wrote:
>
> Hi Xianting,
>
> Thanks for your patch.
>
> On 13 Jun 2022, at 9:10, Xianting Tian wrote:
>
> > Commit 787af64d05cd ("mm: page_alloc: validate buddy before check its migratetype.")
> > added buddy check code. But unfortunately, this fix isn't backported to
> > linux-5.17.y and the former stable branches. The reason is it added wrong
> > fixes message:
> > Fixes: 1dd214b8f21c ("mm: page_alloc: avoid merging non-fallbackable
> > pageblocks with others")
>
> No, the Fixes tag is right. The commit above does need to validate buddy.
I think Xianting is right. The “Fixes:" tag is not accurate and the
page_is_buddy() is necessary here.
This patch could be applied to the early version of the stable tree
(eg: Linux-5.10.y, not the master tree)
>
> > Actually, this issue is involved by commit:
> > commit d9dddbf55667 ("mm/page_alloc: prevent merging between isolated and other pageblocks")
> >
> > For RISC-V arch, the first 2M is reserved for sbi, so the start PFN is 512,
> > but it got buddy PFN 0 for PFN 0x2000:
> > 0 = 0x2000 ^ (1 << 12)
> > With the illegal buddy PFN 0, it got an illegal buddy page, which caused
> > crash in __get_pfnblock_flags_mask().
>
> It seems that the RISC-V arch reveals a similar bug from d9dddbf55667.
> Basically, this bug will only happen when PFN=0x2000 is merging up and
> there are some isolated pageblocks.
Not PFN=0x2000, it's PFN=0x1000, I guess.
RISC-V's first 2MB RAM could reserve for opensbi, so it would have
riscv_pfn_base=512 and mem_map began with 512th PFN when
CONFIG_FLATMEM=y.
(Also, csky has the same issue: a non-zero pfn_base in some scenarios.)
But __find_buddy_pfn algorithm thinks the start address is 0, it could
get 0 pfn or less than the pfn_base value. We need another check to
prevent that.
>
> BTW, what does first reserved 2MB imply? All 4KB pages from first 2MB are
> set to PageReserved?
>
> >
> > With the patch, it can avoid the calling of get_pageblock_migratetype() if
> > it isn't buddy page.
>
> You might miss the __find_buddy_pfn() caller in unset_migratetype_isolate()
> from mm/page_isolation.c, if you are talking about linux-5.17.y and former
> version. There, page_is_buddy() is also not called and is_migrate_isolate_page()
> is called, which calls get_pageblock_migratetype() too.
>
> >
> > 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/page_alloc.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index b1caa1c6c887..5b423caa68fd 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -1129,6 +1129,9 @@ static inline void __free_one_page(struct page *page,
> >
> > buddy_pfn = __find_buddy_pfn(pfn, order);
> > buddy = page + (buddy_pfn - pfn);
> > +
> > + if (!page_is_buddy(page, buddy, order))
> > + goto done_merging;
> > buddy_mt = get_pageblock_migratetype(buddy);
> >
> > if (migratetype != buddy_mt
> > --
> > 2.17.1
>
> --
> Best Regards,
> Yan, Zi
--
Best Regards
Guo Ren
ML: https://lore.kernel.org/linux-csky/
next prev parent reply other threads:[~2022-06-13 19:02 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-13 13:10 [RESEND PATCH] mm: page_alloc: validate buddy before check the migratetype Xianting Tian
2022-06-13 15:22 ` Zi Yan
2022-06-13 16:32 ` Guo Ren [this message]
2022-06-13 19:49 ` Zi Yan
2022-06-13 23:47 ` Guo Ren
2022-06-14 0:14 ` Zi Yan
2022-06-14 1:19 ` Guo Ren
2022-06-14 3:26 ` Xianting Tian
2022-06-15 6:47 ` Xianting Tian
2022-06-15 13:55 ` Zi Yan
2022-06-15 16:15 ` Xianting Tian
2022-06-16 1:51 ` Xianting Tian
2022-06-16 14:01 ` Zi Yan
2022-06-16 15:04 ` David Hildenbrand
2022-06-16 15:16 ` Xianting Tian
2022-06-17 3:17 ` Guo Ren
2022-06-13 16:08 ` Guo Ren
2022-06-14 1:26 ` Xianting Tian
2022-06-14 2:04 ` Xianting Tian
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