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Date:   Wed, 31 Mar 2021 10:18:54 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Alistair Popple <apopple@nvidia.com>
Cc:     linux-mm@kvack.org, nouveau@lists.freedesktop.org,
        bskeggs@redhat.com, akpm@linux-foundation.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        kvm-ppc@vger.kernel.org, dri-devel@lists.freedesktop.org,
        jhubbard@nvidia.com, rcampbell@nvidia.com, jglisse@redhat.com,
        hch@infradead.org, daniel@ffwll.ch, willy@infradead.org,
        Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v7 5/8] mm: Device exclusive memory access
Message-ID: <20210331131854.GI1463678@nvidia.com>
References: <20210326000805.2518-1-apopple@nvidia.com>
 <20210326000805.2518-6-apopple@nvidia.com>
 <20210330193234.GA2356281@nvidia.com>
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On Wed, Mar 31, 2021 at 11:59:28PM +1100, Alistair Popple wrote:

> I guess that makes sense as the split could go either way at the
> moment but I should add a check to make sure this isn't used with
> pinned pages anyway.

Is it possible to have a pinned page under one of these things? If I
pin it before you migrate it then it remains pinned but hidden under
the swap entry?

So the special logic is needed and the pinned page has to be copied
and written as a normal pte, not dropped as a migration entry

Jason