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Date: Mon, 2 May 2016 21:14:04 +0200
From: Andrea Arcangeli <aarcange@redhat.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Jerome Glisse <j.glisse@gmail.com>, Oleg Nesterov <oleg@redhat.com>,
        Hugh Dickins <hughd@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alex Williamson <alex.williamson@redhat.com>,
        kirill.shutemov@linux.intel.com, linux-kernel@vger.kernel.org,
        "linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: Re: GUP guarantees wrt to userspace mappings
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On Mon, May 02, 2016 at 07:12:52PM +0300, Kirill A. Shutemov wrote:
> Any reason why mmu_notifier is not an option?

No way to trigger an hardware re-tried secondary MMU fault as result
of PCI DMA memory access, and expensive to do an MMU notifier
invalidate if it requires waiting for the DMA to complete (but since
MMU notifier is now sleepable the latter is a secondary concern).