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Date:   Fri, 11 Feb 2022 17:49:08 +0100
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Subject: Re: [PATCH v6 01/10] mm: add zone device coherent type memory support
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To:     Jason Gunthorpe <jgg@nvidia.com>
Cc:     Alex Sierra <alex.sierra@amd.com>, akpm@linux-foundation.org,
        Felix.Kuehling@amd.com, linux-mm@kvack.org, rcampbell@nvidia.com,
        linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org,
        amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        hch@lst.de, jglisse@redhat.com, apopple@nvidia.com,
        willy@infradead.org
References: <20220201154901.7921-1-alex.sierra@amd.com>
 <20220201154901.7921-2-alex.sierra@amd.com>
 <beb38138-2266-1ff8-cc82-8fe914bed862@redhat.com>
 <20220211164537.GO4160@nvidia.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
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On 11.02.22 17:45, Jason Gunthorpe wrote:
> On Fri, Feb 11, 2022 at 05:15:25PM +0100, David Hildenbrand wrote:
> 
>> ... I'm pretty sure we cannot FOLL_PIN DEVICE_PRIVATE pages
> 
> Currently the only way to get a DEVICE_PRIVATE page out of the page
> tables is via hmm_range_fault() and that doesn't manipulate any ref
> counts.

Thanks for clarifying Jason! ... and AFAIU, device exclusive entries are
essentially just pointers at ordinary PageAnon() pages. So with DEVICE
COHERENT we'll have the first PageAnon() ZONE_DEVICE pages mapped as
present in the page tables where GUP could FOLL_PIN them.


-- 
Thanks,

David / dhildenb