linux-kernel - RE: [PATCH 1/1] fbdev/hyperv_fb: Fix logic error for Gen2 VMs in hvfb

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Date: Fri, 9 Feb 2024 15:23:33 +0000
From: Michael Kelley <mhklinux@...look.com>
To: "wei.liu@...nel.org" <wei.liu@...nel.org>, "deller@....de" <deller@....de>
CC: "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>, Thomas
 Zimmermann <tzimmermann@...e.de>, "haiyangz@...rosoft.com"
	<haiyangz@...rosoft.com>, "decui@...rosoft.com" <decui@...rosoft.com>,
	"drawat.floss@...il.com" <drawat.floss@...il.com>, "javierm@...hat.com"
	<javierm@...hat.com>, "daniel@...ll.ch" <daniel@...ll.ch>,
	"airlied@...il.com" <airlied@...il.com>
Subject: RE: [PATCH 1/1] fbdev/hyperv_fb: Fix logic error for Gen2 VMs in
 hvfb_getmem()

From: Thomas Zimmermann <tzimmermann@...e.de> Sent: Thursday, February 1, 2024 12:17 AM
> 
> Hi
> 
> Am 01.02.24 um 07:00 schrieb mhkelley58@...il.com:
> > From: Michael Kelley <mhklinux@...look.com>
> >
> > A recent commit removing the use of screen_info introduced a logic
> > error. The error causes hvfb_getmem() to always return -ENOMEM
> > for Generation 2 VMs. As a result, the Hyper-V frame buffer
> > device fails to initialize. The error was introduced by removing
> > an "else if" clause, leaving Gen2 VMs to always take the -ENOMEM
> > error path.
> >
> > Fix the problem by removing the error path "else" clause. Gen 2
> > VMs now always proceed through the MMIO memory allocation code,
> > but with "base" and "size" defaulting to 0.
> 
> Indeed, that's how it was supposed to work. IDK how I didn't notice this
> bug. Thanks a lot for the fix.
> 
> >
> > Fixes: 0aa0838c84da ("fbdev/hyperv_fb: Remove firmware framebufferswith aperture helpers")
> > Signed-off-by: Michael Kelley <mhklinux@...look.com>
> 
> Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>

Wei Liu and Helge Deller --

Should this fix go through the Hyper-V tree or the fbdev tree?   I'm not
aware of a reason that it really matters, but it needs to be one or the
other, and sooner rather than later, because the Hyper-V driver is broken
starting in 6.8-rc1.

Michael

> 
> > ---
> >   drivers/video/fbdev/hyperv_fb.c | 2 --
> >   1 file changed, 2 deletions(-)
> >
> > diff --git a/drivers/video/fbdev/hyperv_fb.c
> b/drivers/video/fbdev/hyperv_fb.c
> > index c26ee6fd73c9..8fdccf033b2d 100644
> > --- a/drivers/video/fbdev/hyperv_fb.c
> > +++ b/drivers/video/fbdev/hyperv_fb.c
> > @@ -1010,8 +1010,6 @@ static int hvfb_getmem(struct hv_device *hdev,
> struct fb_info *info)
> >   			goto getmem_done;
> >   		}
> >   		pr_info("Unable to allocate enough contiguous physical memory on Gen 1 VM. Using MMIO instead.\n");
> > -	} else {
> > -		goto err1;
> >   	}
> >
> >   	/*
>