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From: Daniel Vetter <email@example.com>
To: Javier Martinez Canillas <firstname.lastname@example.org>
Cc: Thomas Zimmermann <email@example.com>,
firstname.lastname@example.org, "H . Peter Anvin" <email@example.com>,
Maarten Lankhorst <firstname.lastname@example.org>,
email@example.com, Greg Kroah-Hartman <firstname.lastname@example.org>,
email@example.com, Thomas Gleixner <firstname.lastname@example.org>,
Maxime Ripard <email@example.com>,
Borislav Petkov <firstname.lastname@example.org>,
Peter Robinson <email@example.com>,
Hans de Goede <firstname.lastname@example.org>,
email@example.com, Ingo Molnar <firstname.lastname@example.org>,
David Airlie <email@example.com>
Subject: Re: [RFC PATCH 0/4] Allow to use DRM fbdev emulation layer with CONFIG_FB disabled
Date: Thu, 2 Sep 2021 16:31:03 +0200 [thread overview]
Message-ID: <YTDgJzhOHEQ5ov3x@phenom.ffwll.local> (raw)
On Wed, Sep 01, 2021 at 11:08:10AM +0200, Javier Martinez Canillas wrote:
> On 8/31/21 2:35 PM, Daniel Vetter wrote:
> > On Sat, Aug 28, 2021 at 12:02:21AM +0200, Javier Martinez Canillas wrote:
> >> We talked about a drmcon with Peter Robinson as well but then decided that a
> >> way to disable CONFIG_FB but still having the DRM fbdev emulation could be a
> >> intermediary step, hence these RFC patches.
> >> But yes, I agree that a drmcon would be the proper approach for this, to not
> >> need any fbdev support at all. We will just keep the explicit disable for the
> >> fbdev drivers then in the meantime.
> > I think the only intermediate step would be to disable the fbdev uapi
> > (char node and anything in sysfs), while still registering against the
> > fbcon layer so you have a console.
> Right, $subject disabled the sysfs interface but left the fbdev chardev. I can
> try to do a v2 that also disables that interface but just keep the fbcon part.
> > But looking at the things syzbot finds the really problematic code is all
> > in the fbcon and console layer in general, and /dev/fb0 seems pretty
> > solid.
> Yes, but still would be an improvement in the sense that no legacy fbdev uAPI
> will be exposed and so user-space would only depend on the DRM/KMS interface.
> > I think for a substantial improvement here in robustness what you really
> > want is
> > - kmscon in userspace
> > - disable FB layer
> > - ideally also disable console/vt layer in the kernel
> Earlier in the thread it was mentioned that an in-kernel drmcon could be used
> instead. My worry with kmscon is that moving something as critical as console
> output to user-space might make harder to troubleshoot early booting issues.
> And also that will require user-space changes. An in-kernel drmcon could be a
> drop-in replacement though.
The drmcon wouldn't be a full console, but just an emergency log renderer.
See Sam's reply, he found the series again.
The real attack surface reduction is in getting rid of the console/vt uapi
implementation from the kernel.
> > - have a minimal emergency/boot-up log thing in drm, patches for that
> > floated around a few times
> Interesting. Do you have any pointers for this? My search-fu failed me when
> trying to find these patches.
> Best regards,
> Javier Martinez Canillas
> Linux Engineering
> Red Hat
Software Engineer, Intel Corporation
next prev parent reply other threads:[~2021-09-02 14:31 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-27 10:00 Javier Martinez Canillas
2021-08-27 10:00 ` [RFC PATCH 1/4] fbdev: Rename fb_*_device() functions names to match what they do Javier Martinez Canillas
2021-08-27 17:50 ` [RFC PATCH 0/4] Allow to use DRM fbdev emulation layer with CONFIG_FB disabled Thomas Zimmermann
2021-08-27 20:20 ` Daniel Vetter
2021-08-27 22:02 ` Javier Martinez Canillas
2021-08-31 12:35 ` Daniel Vetter
2021-09-01 9:08 ` Javier Martinez Canillas
2021-09-02 14:31 ` Daniel Vetter [this message]
[not found] <YS+Lhz9gg/0Caafirstname.lastname@example.org>
2021-09-09 15:52 ` Noralf Trønnes
2021-09-09 16:27 ` Noralf Trønnes
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