linux-kernel - Re: mmu notifier calls in apply_to_page

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Date:	Fri, 09 Jul 2010 10:30:48 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Andrea Arcangeli <aarcange@...hat.com>
CC:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: mmu notifier calls in apply_to_page_range()

On 07/09/2010 09:22 AM, Andrea Arcangeli wrote:
> mmu notifier only relevant for userland mappings, not kernel
> mappings. I don't know about the xen use, but for vmalloc certainly it
> can't be a problem to remove those two mmu notifier invalidates.
>
> Only bit that is worrysome is the mm == &init_mm
> pte_alloc_kernel|pte_alloc_map_lock. That seems to imply it may also
> be used to mangle over userland. But apparently all users are passing
> &init_mm as expected. I guess if you remove the mm parameter and you
> default to &init_mm definitely there will be no risk in removing the
> mmu notifier range_start/end invalidates.
>   

No, we do have some users which use it on user memory.  But those users
are using it as part of their own mmu notifier backend, so the recursive
calls are causing a problem.  My point is that anyone using
apply_to_page_range should be making their own calls to mmu notifiers as
appropriate to whatever they're doing.

    J

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