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

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Message-ID: <20201106125840.GP36674@ziepe.ca>
Date:   Fri, 6 Nov 2020 08:58:40 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Daniel Vetter <daniel@...ll.ch>
Cc:     John Hubbard <jhubbard@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        J??r??me Glisse <jglisse@...hat.com>,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        Jan Kara <jack@...e.cz>, Pawel Osciak <pawel@...iak.com>,
        KVM list <kvm@...r.kernel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Tomasz Figa <tfiga@...omium.org>,
        Linux MM <linux-mm@...ck.org>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>
Subject: Re: [PATCH v5 05/15] mm/frame-vector: Use FOLL_LONGTERM

On Fri, Nov 06, 2020 at 11:01:57AM +0100, Daniel Vetter wrote:

> gpu drivers also tend to use vmf_insert_pfn* directly, so we can do
> on-demand paging and move buffers around. From what I glanced for
> lowest level we to the pte_mkspecial correctly (I think I convinced
> myself that vm_insert_pfn does that), but for pud/pmd levels it seems
> just yolo.
> 
> remap_pfn_range seems to indeed split down to pte level always.

Thats what it looked like to me too.
 
> >  From my reading, yes. See ioremap_try_huge_pmd().
> 
> The ioremap here shouldn't matter, since this is for kernel-internal
> mappings. So that's all fine I think.

Right, sorry to be unclear, we are talking about io_remap_pfn_range()
which is for userspace mappings in VMAs

Jason