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Date:   Wed, 31 Mar 2021 10:46:04 -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: <20210331134604.GK1463678@nvidia.com>
References: <20210326000805.2518-1-apopple@nvidia.com>
 <2521635.masqiumSp9@nvdebian>
 <20210331131854.GI1463678@nvidia.com>
 <2124945.3NMGunUBXV@nvdebian>
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On Thu, Apr 01, 2021 at 12:27:52AM +1100, Alistair Popple wrote:
> On Thursday, 1 April 2021 12:18:54 AM AEDT Jason Gunthorpe wrote:
> > 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?
> 
> At the moment yes. But I had planned (and this reminded me) to add a check to 
> prevent marking pinned pages for exclusive access. 

How do you even do that without races with GUP fast?

Jason