From: Greg KH <gregkh@linuxfoundation.org>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Vlastimil Babka" <vbabka@suse.cz>,
"Naoya Horiguchi" <n-horiguchi@ah.jp.nec.com>,
"Davidlohr Bueso" <dave@stgolabs.net>,
"Michal Hocko" <mhocko@kernel.org>,
"Andrew Morton" <akpm@linux-foundation.org>,
stable@vger.kernel.org
Subject: Re: [PATCH v2] mm: migration: fix migration of huge PMD shared pages
Date: Tue, 14 Aug 2018 08:28:13 +0200 [thread overview]
Message-ID: <20180814062813.GA22413@kroah.com> (raw)
In-Reply-To: <20180814003058.19732-1-mike.kravetz@oracle.com>
On Mon, Aug 13, 2018 at 05:30:58PM -0700, Mike Kravetz wrote:
> The page migration code employs try_to_unmap() to try and unmap the
> source page. This is accomplished by using rmap_walk to find all
> vmas where the page is mapped. This search stops when page mapcount
> is zero. For shared PMD huge pages, the page map count is always 1
> no matter the number of mappings. Shared mappings are tracked via
> the reference count of the PMD page. Therefore, try_to_unmap stops
> prematurely and does not completely unmap all mappings of the source
> page.
>
> This problem can result is data corruption as writes to the original
> source page can happen after contents of the page are copied to the
> target page. Hence, data is lost.
>
> This problem was originally seen as DB corruption of shared global
> areas after a huge page was soft offlined due to ECC memory errors.
> DB developers noticed they could reproduce the issue by (hotplug)
> offlining memory used to back huge pages. A simple testcase can
> reproduce the problem by creating a shared PMD mapping (note that
> this must be at least PUD_SIZE in size and PUD_SIZE aligned (1GB on
> x86)), and using migrate_pages() to migrate process pages between
> nodes while continually writing to the huge pages being migrated.
>
> To fix, have the try_to_unmap_one routine check for huge PMD sharing
> by calling huge_pmd_unshare for hugetlbfs huge pages. If it is a
> shared mapping it will be 'unshared' which removes the page table
> entry and drops the reference on the PMD page. After this, flush
> caches and TLB.
>
> Fixes: 39dde65c9940 ("shared page table for hugetlb page")
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
> ---
> v2: Fixed build issue for !CONFIG_HUGETLB_PAGE and typos in comment
>
<formletter>
This is not the correct way to submit patches for inclusion in the
stable kernel tree. Please read:
https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.
</formletter>
next prev parent reply other threads:[~2018-08-14 6:28 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-13 3:41 [PATCH] mm: migration: fix migration of huge PMD shared pages Mike Kravetz
2018-08-13 4:10 ` kbuild test robot
2018-08-14 0:30 ` [PATCH v2] " Mike Kravetz
2018-08-14 6:28 ` Greg KH [this message]
2018-08-13 4:17 ` [PATCH] " kbuild test robot
2018-08-13 10:58 ` Kirill A. Shutemov
2018-08-13 23:21 ` Mike Kravetz
2018-08-14 8:48 ` Kirill A. Shutemov
2018-08-15 0:15 ` Mike Kravetz
2018-08-15 8:47 ` Kirill A. Shutemov
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