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

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Date:   Thu, 5 Nov 2020 20:08:10 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Jason Gunthorpe <jgg@...pe.ca>,
        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 11/5/20 4:49 AM, Jason Gunthorpe wrote:
> On Thu, Nov 05, 2020 at 10:25:24AM +0100, Daniel Vetter wrote:
>>> /*
>>>   * If we can't determine whether or not a pte is special, then fail immediately
>>>   * for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not
>>>   * to be special.
>>>   *
>>>   * For a futex to be placed on a THP tail page, get_futex_key requires a
>>>   * get_user_pages_fast_only implementation that can pin pages. Thus it's still
>>>   * useful to have gup_huge_pmd even if we can't operate on ptes.
>>>   */
>>
>> We support hugepage faults in gpu drivers since recently, and I'm not
>> seeing a pud_mkhugespecial anywhere. So not sure this works, but probably
>> just me missing something again.
> 
> It means ioremap can't create an IO page PUD, it has to be broken up.
> 
> Does ioremap even create anything larger than PTEs?
> 

 From my reading, yes. See ioremap_try_huge_pmd().

thanks,
-- 
John Hubbard
NVIDIA