Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 21 Oct 2020 13:37:02 -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: <20201021163702.GM36674@ziepe.ca>
References: <20201021085655.1192025-1-daniel.vetter@ffwll.ch>
 <20201021085655.1192025-13-daniel.vetter@ffwll.ch>
 <20201021125030.GK36674@ziepe.ca>
 <CAKMK7uEWe8CaT7zjcZ6dJAKHxtxtqzjVB35fCFviwhcnqksDfw@mail.gmail.com>
 <20201021151352.GL36674@ziepe.ca>
 <CAKMK7uGq0=ks7Zj1Et44k7x9FwE9u_ua4zANSqrLRri0v01V+Q@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAKMK7uGq0=ks7Zj1Et44k7x9FwE9u_ua4zANSqrLRri0v01V+Q@mail.gmail.com>
Precedence: bulk

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 guess one option would be if remap_pfn_range would steal the
> vma->vm_ops pointer for itself, then it could set up the correct
> ->install_ptes hook. But there's tons of callers for that, so not sure
> that's a bright idea.

The caller has to check that the mapping is still live, and I think
hold a lock across the remap? Auto-defering it doesn't seem feasible.

Jason