Re: [PATCH v2 07/11] video/aperture: Disable and unregister sysfb devices via aperture helpers

From: "Samuel Čavoj" <samuel@cavoj.net>
To: Javier Martinez Canillas <javierm@redhat.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>,
	deller@gmx.de, daniel@ffwll.ch, sam@ravnborg.org,
	maxime@cerno.tech, linux-fbdev@vger.kernel.org,
	linux-staging@lists.linux.dev, dri-devel@lists.freedesktop.org,
	Zack Rusin <zackr@vmware.com>,
	Daniel Vetter <daniel.vetter@ffwll.ch>,
	Alex Deucher <alexander.deucher@amd.com>,
	Zhen Lei <thunder.leizhen@huawei.com>,
	Changcheng Deng <deng.changcheng@zte.com.cn>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <mripard@kernel.org>
Subject: Re: [PATCH v2 07/11] video/aperture: Disable and unregister sysfb devices via aperture helpers
Date: Mon, 20 Mar 2023 12:08:13 +0100	[thread overview]
Message-ID: <87706a167c1e490a12371e2edf0f34e3@cavoj.net> (raw)
In-Reply-To: <874jqfpw7k.fsf@minerva.mail-host-address-is-not-set>

On 2023-03-20 11:13, Javier Martinez Canillas wrote:
> Thomas Zimmermann <tzimmermann@suse.de> writes:
> 
> [...]
> 
>>>> +    /*
>>>> +     * If a driver asked to unregister a platform device registered 
>>>> by
>>>> +     * sysfb, then can be assumed that this is a driver for a 
>>>> display
>>>> +     * that is set up by the system firmware and has a generic 
>>>> driver.
>>>> +     *
>>>> +     * Drivers for devices that don't have a generic driver will 
>>>> never
>>>> +     * ask for this, so let's assume that a real driver for the 
>>>> display
>>>> +     * was already probed and prevent sysfb to register devices 
>>>> later.
>>>> +     */
>>>> +    sysfb_disable();
>>> 
>>> This call to sysfb_disable() has been causing trouble with regard to
>>> VFIO. VFIO has been calling aperture_remove_conflicting_pci_devices 
>>> to
>>> get rid of any console drivers (d173780620792c) using the device in
>>> question, but now even unrelated drivers are getting killed. Example
>>> situation:
>> 
>> Which drivers do you use?

This happens with either no drivers loaded or the proprietary nvidia
driver. Nouveau is fine as it doesn't rely on efifb but brings its own.

>> 
> 
> Also, what kernel version?

I tried with 6.2.6, can build mainline and test there as well.

Thanks for help!

> 
> [...]
> 
>>> 
>>> Machine has two GPUs and uses efifb for the console. Efifb registers
>>> with the aperture system the efi framebuffer region, which is covered
>>> by a BAR resource of GPU 1. VFIO grabs GPU 2 and calls
>>> aperture_remove_conflicting_pci_devices(GPU 2). GPU 2 has no overlap
>>> with the efifb on GPU1 but the efifb is killed regardless due to
>>> the unconditional call to sysfb_disable(). The console switches
>>> to dummy and locks up from the user perspective.
>>> This seems unnecessary, as the device is unrelated.
>>> 
> 
> That's a bug indeed but I thought that was already fixed...