linux-kernel - Re: [PATCH v5 05/15] mm/frame-vector: Use FOLL

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Message-ID: <20201104140023.GQ36674@ziepe.ca>
Date:   Wed, 4 Nov 2020 10:00:23 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     John Hubbard <jhubbard@...dia.com>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        KVM list <kvm@...r.kernel.org>, Linux MM <linux-mm@...ck.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Pawel Osciak <pawel@...iak.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        Jan Kara <jack@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v5 05/15] mm/frame-vector: Use FOLL_LONGTERM

On Sun, Nov 01, 2020 at 11:50:39PM +0100, Daniel Vetter wrote:

> It's not device drivers, but everyone else. At least my understanding
> is that VM_IO | VM_PFNMAP means "even if it happens to be backed by a
> struct page, do not treat it like normal memory". And gup/pup_fast
> happily break that. I tried to chase the history of that test, didn't
> turn up anything I understood much:

VM_IO isn't suppose do thave struct pages, so how can gup_fast return
them?

I thought some magic in the PTE flags excluded this?

Jason