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

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Date:   Mon, 9 Nov 2020 16:19:44 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>
Cc:     Daniel Vetter <daniel@...ll.ch>,
        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 Mon, Nov 09, 2020 at 09:44:02AM +0100, Thomas Hellström wrote:
> static inline bool vma_is_special_huge(const struct vm_area_struct
> *vma)
> {
> 	return vma_is_dax(vma) || (vma->vm_file &&
> 				   (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP)));
> }

That is testing a VMA, not a PTE, which doesn't help protect
get_user_pages_fast.

Sounds like is has opened a big user crashy problem in DRM and the
huge page stuff needs to be revereted..

Dan?

Jason