RE: [bug report] Commit ccf953d8f3d6 ("fb_defio: Remove custom address_space_operations") breaks Hyper-V FB driver

From: Vineeth Pillai <redacted>
Sent: Friday, June 4, 2021 8:47 AM
To: Wei Liu <wei.liu@kernel.org>; vkuznets <vkuznets@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>; dri-devel@lists.freedesktop.org;
linux-hyperv@vger.kernel.org; linux-fbdev@vger.kernel.org;
linux-kernel@vger.kernel.org; Michael Kelley [off-list ref];
Dexuan Cui [off-list ref]
Subject: Re: [bug report] Commit ccf953d8f3d6 ("fb_defio: Remove custom
address_space_operations") breaks Hyper-V FB driver


On 6/4/2021 9:00 AM, Wei Liu wrote:

quoted

On Fri, Jun 04, 2021 at 02:25:01PM +0200, Vitaly Kuznetsov wrote:

quoted

Hi,

Commit ccf953d8f3d6 ("fb_defio: Remove custom

address_space_operations")

quoted

quoted

seems to be breaking Hyper-V framebuffer
(drivers/video/fbdev/hyperv_fb.c) driver for me: Hyper-V guest boots
well and plymouth even works but when I try starting Gnome, virtual
screen just goes black. Reverting the above mentioned commit on top of
5.13-rc4 saves the day. The behavior is 100% reproducible. I'm using
Gen2 guest runing on Hyper-V 2019. It was also reported that Gen1 guests
are equally broken.

Is this something known?

I've heard a similar report from Vineeth but we didn't get to the bottom
of this.

I have just tried reverting the commit mentioned above and it solves the
GUI freeze
I was also seeing. Previously, login screen was just freezing, but VM
was accessible
through ssh. With the above commit reverted, I can login to Gnome.

Looks like I am also experiencing the same bug mentioned here.

Thanks,
Vineeth

As Matthew mentioned, this is a known issue:
https://lwn.net/ml/linux-kernel/YLZEhv0cpZp8uVE3@casper.infradead.org/

Matthew has reverted ccf953d8f3d6:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0b78f8bcf4951af30b0ae83ea4fad27d641ab617
so the latest mainline should work now.

Thanks,
Dexuan