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Subject: Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame
 Ownership (XPFO)
From:   Dave Hansen <dave.hansen@intel.com>
To:     Tycho Andersen <tycho@docker.com>
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Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        kernel-hardening@lists.openwall.com,
        Marco Benatto <marco.antonio.780@gmail.com>,
        Juerg Haefliger <juerg.haefliger@canonical.com>, x86@kernel.org
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Date:   Mon, 13 Nov 2017 14:46:25 -0800
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On 11/13/2017 02:20 PM, Dave Hansen wrote:
> On 11/09/2017 05:09 PM, Tycho Andersen wrote:
>> which I guess is from the additional flags in grow_dev_page() somewhere down
>> the stack. Anyway... it seems this is a kernel allocation that's using
>> MIGRATE_MOVABLE, so perhaps we need some more fine tuned heuristic than just
>> all MOVABLE allocations are un-mapped via xpfo, and all the others are mapped.
>>
>> Do you have any ideas?
> 
> It still has to do a kmap() or kmap_atomic() to be able to access it.  I
> thought you hooked into that.  Why isn't that path getting hit for these?

Oh, this looks to be accessing data mapped by a buffer_head.  It
(rudely) accesses data via:

void set_bh_page(struct buffer_head *bh,
...
	bh->b_data = page_address(page) + offset;


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