From: Simon Ser <contact@emersion.fr>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: "Daniel Stone" <daniel@fooishbar.org>,
"Hans de Goede" <hdegoede@redhat.com>,
"Maxime Ripard" <mripard@redhat.com>,
"Sumit Semwal" <sumit.semwal@linaro.org>,
"Benjamin Gaignard" <benjamin.gaignard@collabora.com>,
"Brian Starkey" <Brian.Starkey@arm.com>,
"John Stultz" <jstultz@google.com>,
"T.J. Mercier" <tjmercier@google.com>,
"Christian König" <christian.koenig@amd.com>,
"Lennart Poettering" <mzxreary@0pointer.de>,
"Robert Mader" <robert.mader@collabora.com>,
"Sebastien Bacher" <sebastien.bacher@canonical.com>,
"Linux Media Mailing List" <linux-media@vger.kernel.org>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>,
linaro-mm-sig@lists.linaro.org,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"Bryan O'Donoghue" <bryan.odonoghue@linaro.org>,
"Milan Zamazal" <mzamazal@redhat.com>,
"Andrey Konovalov" <andrey.konovalov.ynk@gmail.com>
Subject: Re: Safety of opening up /dev/dma_heap/* to physically present users (udev uaccess tag) ?
Date: Mon, 13 May 2024 13:51:23 +0000 [thread overview]
Message-ID: <IXDM2ci-eGvU9RQkT6a52vcV66vr8d0ywbDRFY8gBjjNuMyv8RDgdJS0PvvfnKuPR1fXINPUjOBkKx4vIcshSb2Y11xd3DjfDQ-Np8VIFgQ=@emersion.fr> (raw)
In-Reply-To: <Zjue98r4ZgGbMN5K@phenom.ffwll.local>
On Wednesday, May 8th, 2024 at 17:49, Daniel Vetter <daniel@ffwll.ch> wrote:
> On Wed, May 08, 2024 at 09:38:33AM +0100, Daniel Stone wrote:
>
> > On Wed, 8 May 2024 at 09:33, Daniel Vetter daniel@ffwll.ch wrote:
> >
> > > On Wed, May 08, 2024 at 06:46:53AM +0100, Daniel Stone wrote:
> > >
> > > > That would have the unfortunate side effect of making sandboxed apps
> > > > less efficient on some platforms, since they wouldn't be able to do
> > > > direct scanout anymore ...
> > >
> > > I was assuming that everyone goes through pipewire, and ideally that is
> > > the only one that can even get at these special chardev.
> > >
> > > If pipewire is only for sandboxed apps then yeah this aint great :-/
> >
> > No, PipeWire is fine, I mean graphical apps.
> >
> > Right now, if your platform requires CMA for display, then the app
> > needs access to the GPU render node and the display node too, in order
> > to allocate buffers which the compositor can scan out directly. If it
> > only has access to the render nodes and not the display node, it won't
> > be able to allocate correctly, so its content will need a composition
> > pass, i.e. performance penalty for sandboxing. But if it can allocate
> > correctly, then hey, it can exhaust CMA just like heaps can.
> >
> > Personally I think we'd be better off just allowing access and
> > figuring out cgroups later. It's not like the OOM story is great
> > generally, and hey, you can get there with just render nodes ...
>
> Imo the right fix is to ask the compositor to allocate the buffers in this
> case, and then maybe have some kind of revoke/purge behaviour on these
> buffers. Compositor has an actual idea of who's a candidate for direct
> scanout after all, not the app. Or well at least force migrate the memory
> from cma to shmem.
>
> If you only whack cgroups on this issue you're still stuck in the world
> where either all apps together can ddos the display or no one can
> realistically direct scanout.
>
> So yeah on the display side the problem isn't solved either, but we knew
> that already.
What makes scanout memory so special?
The way I see it, any kind of memory will always be a limited resource:
regular programs can exhaust system memory, as well as GPU VRAM, as well
as scanout memory. I think we need to have ways to limit/control/arbiter
the allocations regardless, and I don't think scanout memory should be a
special case here.
next prev parent reply other threads:[~2024-05-13 13:51 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-06 11:49 Safety of opening up /dev/dma_heap/* to physically present users (udev uaccess tag) ? Hans de Goede
2024-05-06 12:05 ` Maxime Ripard
2024-05-06 12:11 ` Hans de Goede
2024-05-06 13:38 ` Daniel Vetter
2024-05-06 14:01 ` Hans de Goede
2024-05-07 11:15 ` Daniel Vetter
2024-05-08 5:46 ` Daniel Stone
2024-05-08 8:33 ` Daniel Vetter
2024-05-08 8:38 ` Daniel Stone
2024-05-08 15:49 ` Daniel Vetter
2024-05-09 9:23 ` Daniel Stone
2024-05-16 10:18 ` Daniel Vetter
2024-05-13 13:51 ` Simon Ser [this message]
2024-05-16 10:13 ` Daniel Vetter
2024-05-16 11:49 ` Christian König
2024-05-07 13:34 ` Dmitry Baryshkov
2024-05-07 18:59 ` Laurent Pinchart
2024-05-22 13:34 ` Maxime Ripard
2024-05-23 9:41 ` Daniel Vetter
2024-05-07 13:32 ` Dmitry Baryshkov
2024-05-07 14:34 ` Hans de Goede
2024-05-07 15:09 ` Dmitry Baryshkov
2024-05-07 15:15 ` Bryan O'Donoghue
2024-05-07 15:19 ` Dmitry Baryshkov
2024-05-07 18:40 ` Laurent Pinchart
2024-05-07 19:59 ` Dmitry Baryshkov
2024-05-07 20:15 ` Laurent Pinchart
2024-05-08 8:39 ` Daniel Vetter
2024-05-08 21:54 ` Laurent Pinchart
2024-05-13 8:39 ` Maxime Ripard
2024-05-07 17:36 ` Daniel Vetter
2024-05-07 18:36 ` Laurent Pinchart
2024-05-07 20:07 ` Nicolas Dufresne
2024-05-08 8:36 ` Daniel Vetter
2024-05-08 21:51 ` Laurent Pinchart
2024-05-08 21:52 ` Laurent Pinchart
2024-05-13 8:29 ` Maxime Ripard
2024-05-13 8:34 ` Laurent Pinchart
2024-05-13 15:10 ` Nicolas Dufresne
2024-05-14 20:42 ` Laurent Pinchart
2024-05-15 17:43 ` nicolas.dufresne
2024-05-16 11:27 ` Laurent Pinchart
2024-05-16 17:11 ` nicolas.dufresne
2024-05-21 8:43 ` Maxime Ripard
2024-05-21 14:18 ` nicolas.dufresne
2024-05-16 7:00 ` Simon Ser
2024-05-16 11:20 ` Laurent Pinchart
2024-05-22 13:02 ` Nicolas Dufresne
2024-05-13 13:42 ` Nicolas Dufresne
2024-05-13 13:51 ` Maxime Ripard
2024-05-13 15:06 ` Nicolas Dufresne
2024-05-14 20:45 ` Laurent Pinchart
2024-05-14 20:52 ` Nicolas Dufresne
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