linux-kernel - Re: [Intel-gfx] [PATCH 2/2] drm: share address space for dma bufs

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Message-ID: <20191122063236.vs3bh6xvmswlszte@sirius.home.kraxel.org>
Date:   Fri, 22 Nov 2019 07:32:36 +0100
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     "Ruhl, Michael J" <michael.j.ruhl@...el.com>
Cc:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        David Airlie <airlied@...ux.ie>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>,
        Maxime Ripard <mripard@...nel.org>
Subject: Re: [Intel-gfx] [PATCH 2/2] drm: share address space for dma bufs

On Thu, Nov 21, 2019 at 04:42:10PM +0000, Ruhl, Michael J wrote:
> >-----Original Message-----
> >From: Intel-gfx <intel-gfx-bounces@...ts.freedesktop.org> On Behalf Of Gerd
> >Hoffmann
> >Sent: Thursday, November 21, 2019 5:38 AM
> >To: dri-devel@...ts.freedesktop.org
> >Cc: David Airlie <airlied@...ux.ie>; intel-gfx@...ts.freedesktop.org; open list
> ><linux-kernel@...r.kernel.org>; Maxime Ripard <mripard@...nel.org>; Gerd
> >Hoffmann <kraxel@...hat.com>
> >Subject: [Intel-gfx] [PATCH 2/2] drm: share address space for dma bufs
> >
> >Use the shared address space of the drm device (see drm_open() in
> >drm_file.c) for dma-bufs too.  That removes a difference betweem drm
> >device mmap vmas and dma-buf mmap vmas and fixes corner cases like
> >unmaps not working properly.
> 
> Hi Gerd,
> 
> Just want to make sure I understand this...
> 
> So unmaps will not work correctly for mappings when a driver does a
> drm_vma_node_unamp()?

Completely removing the mapping (aka munmap syscall) works fine.
Zapping the pte's (using madvise(dontneed) for example) doesn't.

> This is a day one bug?

I guess so, but I'll leave that to others being active longer than me in
drm hacking to answer ...

cheers,
  Gerd