From: John Hubbard <jhubbard@nvidia.com>
To: Ralph Campbell <rcampbell@nvidia.com>, <linux-mm@kvack.org>
Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org,
"Christoph Hellwig" <hch@lst.de>,
"Dan Williams" <dan.j.williams@intel.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Jason Gunthorpe" <jgg@mellanox.com>,
"Logan Gunthorpe" <logang@deltatee.com>,
"Ira Weiny" <ira.weiny@intel.com>,
"Matthew Wilcox" <willy@infradead.org>,
"Mel Gorman" <mgorman@techsingularity.net>,
"Jan Kara" <jack@suse.cz>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
"Michal Hocko" <mhocko@suse.com>,
"Andrea Arcangeli" <aarcange@redhat.com>,
"Mike Kravetz" <mike.kravetz@oracle.com>,
"Jérôme Glisse" <jglisse@redhat.com>
Subject: Re: [PATCH v2 2/3] mm/hmm: fix ZONE_DEVICE anon page mapping reuse
Date: Fri, 19 Jul 2019 14:45:08 -0700 [thread overview]
Message-ID: <5089cfa6-ba0c-efa8-6beb-6fb1881a57d4@nvidia.com> (raw)
In-Reply-To: <20190719192955.30462-3-rcampbell@nvidia.com>
On 7/19/19 12:29 PM, Ralph Campbell wrote:
> When a ZONE_DEVICE private page is freed, the page->mapping field can be
> set. If this page is reused as an anonymous page, the previous value can
> prevent the page from being inserted into the CPU's anon rmap table.
> For example, when migrating a pte_none() page to device memory:
> migrate_vma(ops, vma, start, end, src, dst, private)
> migrate_vma_collect()
> src[] = MIGRATE_PFN_MIGRATE
> migrate_vma_prepare()
> /* no page to lock or isolate so OK */
> migrate_vma_unmap()
> /* no page to unmap so OK */
> ops->alloc_and_copy()
> /* driver allocates ZONE_DEVICE page for dst[] */
> migrate_vma_pages()
> migrate_vma_insert_page()
> page_add_new_anon_rmap()
> __page_set_anon_rmap()
> /* This check sees the page's stale mapping field */
> if (PageAnon(page))
> return
> /* page->mapping is not updated */
>
> The result is that the migration appears to succeed but a subsequent CPU
> fault will be unable to migrate the page back to system memory or worse.
>
> Clear the page->mapping field when freeing the ZONE_DEVICE page so stale
> pointer data doesn't affect future page use.
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
thanks,
--
John Hubbard
NVIDIA
>
> Fixes: b7a523109fb5c9d2d6dd ("mm: don't clear ->mapping in hmm_devmem_free")
> Cc: stable@vger.kernel.org
> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Jason Gunthorpe <jgg@mellanox.com>
> Cc: Logan Gunthorpe <logang@deltatee.com>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Jan Kara <jack@suse.cz>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Andrea Arcangeli <aarcange@redhat.com>
> Cc: Mike Kravetz <mike.kravetz@oracle.com>
> Cc: "Jérôme Glisse" <jglisse@redhat.com>
> ---
> kernel/memremap.c | 24 ++++++++++++++++++++++++
> 1 file changed, 24 insertions(+)
>
> diff --git a/kernel/memremap.c b/kernel/memremap.c
> index bea6f887adad..98d04466dcde 100644
> --- a/kernel/memremap.c
> +++ b/kernel/memremap.c
> @@ -408,6 +408,30 @@ void __put_devmap_managed_page(struct page *page)
>
> mem_cgroup_uncharge(page);
>
> + /*
> + * When a device_private page is freed, the page->mapping field
> + * may still contain a (stale) mapping value. For example, the
> + * lower bits of page->mapping may still identify the page as
> + * an anonymous page. Ultimately, this entire field is just
> + * stale and wrong, and it will cause errors if not cleared.
> + * One example is:
> + *
> + * migrate_vma_pages()
> + * migrate_vma_insert_page()
> + * page_add_new_anon_rmap()
> + * __page_set_anon_rmap()
> + * ...checks page->mapping, via PageAnon(page) call,
> + * and incorrectly concludes that the page is an
> + * anonymous page. Therefore, it incorrectly,
> + * silently fails to set up the new anon rmap.
> + *
> + * For other types of ZONE_DEVICE pages, migration is either
> + * handled differently or not done at all, so there is no need
> + * to clear page->mapping.
> + */
> + if (is_device_private_page(page))
> + page->mapping = NULL;
> +
> page->pgmap->ops->page_free(page);
> } else if (!count)
> __put_page(page);
>
next prev parent reply other threads:[~2019-07-19 21:45 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-19 19:29 [PATCH v2 0/3] mm/hmm: fixes for device private page migration Ralph Campbell
2019-07-19 19:29 ` [PATCH v2 1/3] mm: document zone device struct page field usage Ralph Campbell
2019-07-19 21:43 ` John Hubbard
2019-07-21 15:05 ` Randy Dunlap
2019-07-21 16:02 ` Matthew Wilcox
2019-07-22 5:13 ` Ira Weiny
2019-07-22 11:08 ` Matthew Wilcox
2019-07-23 21:25 ` Ralph Campbell
2019-07-23 21:39 ` Weiny, Ira
2019-07-22 9:36 ` Christoph Hellwig
2019-07-22 9:37 ` Christoph Hellwig
2019-07-19 19:29 ` [PATCH v2 2/3] mm/hmm: fix ZONE_DEVICE anon page mapping reuse Ralph Campbell
2019-07-19 21:45 ` John Hubbard [this message]
2019-07-22 9:38 ` Christoph Hellwig
2019-07-19 19:29 ` [PATCH v2 3/3] mm/hmm: Fix bad subpage pointer in try_to_unmap_one Ralph Campbell
2019-07-20 12:23 ` Sasha Levin
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