linux-kernel - Re: [PATCH v3 12/16] PCI: Obey iomem restrictions for procfs mmap

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Message-ID: <20201022114345.GO36674@ziepe.ca>
Date:   Thu, 22 Oct 2020 08:43:45 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     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>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        John Hubbard <jhubbard@...dia.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Jan Kara <jack@...e.cz>, Bjorn Helgaas <bhelgaas@...gle.com>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Daniel Vetter <daniel.vetter@...ll.com>
Subject: Re: [PATCH v3 12/16] PCI: Obey iomem restrictions for procfs mmap

On Thu, Oct 22, 2020 at 09:00:44AM +0200, Daniel Vetter wrote:
> On Thu, Oct 22, 2020 at 1:20 AM Jason Gunthorpe <jgg@...pe.ca> wrote:
> >
> > 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@...pe.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()??
> 
> Uh no :-)

So it is fine, the pgoff mangling only happens for MAP_PRIVATE

Jason