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Date:   Wed, 21 Oct 2020 20:20:22 -0300
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Daniel Vetter <daniel.vetter@ffwll.ch>
Cc:     DRI Development <dri-devel@lists.freedesktop.org>,
        LKML <linux-kernel@vger.kernel.org>,
        KVM list <kvm@vger.kernel.org>, Linux MM <linux-mm@kvack.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        linux-samsung-soc <linux-samsung-soc@vger.kernel.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@vger.kernel.org>,
        linux-s390 <linux-s390@vger.kernel.org>,
        Daniel Vetter <daniel.vetter@intel.com>,
        Kees Cook <keescook@chromium.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        John Hubbard <jhubbard@nvidia.com>,
        =?utf-8?B?SsOpcsO0bWU=?= Glisse <jglisse@redhat.com>,
        Jan Kara <jack@suse.cz>, Bjorn Helgaas <bhelgaas@google.com>,
        Linux PCI <linux-pci@vger.kernel.org>,
        Daniel Vetter <daniel.vetter@ffwll.com>
Subject: Re: [PATCH v3 12/16] PCI: Obey iomem restrictions for procfs mmap
Message-ID: <20201021232022.GN36674@ziepe.ca>
References: <20201021085655.1192025-1-daniel.vetter@ffwll.ch>
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On Wed, Oct 21, 2020 at 09:24:08PM +0200, Daniel Vetter wrote:
> On Wed, Oct 21, 2020 at 6:37 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> >
> > On Wed, Oct 21, 2020 at 05:54:54PM +0200, Daniel Vetter wrote:
> >
> > > The trouble is that io_remap_pfn adjust vma->pgoff, so we'd need to
> > > split that. So ideally ->mmap would never set up any ptes.
> >
> > /dev/mem makes pgoff == pfn so it doesn't get changed by remap.
> >
> > pgoff doesn't get touched for MAP_SHARED either, so there are other
> > users that could work like this - eg anyone mmaping IO memory is
> > probably OK.
> 
> I was more generally thinking for io_remap_pfn_users because of the
> mkwrite use-case we might have in fbdev emulation in drm.

You have a use case for MAP_PRIVATE and io_remap_pfn_range()??

Jason