RE: [PATCH 1/1] fbdev/hyperv_fb: Fix logic error for Gen2 VMs in hvfb_getmem()

[Michael Kelley]

From: Thomas Zimmermann <tzimmermann@xxxxxxx> Sent: Thursday, February 1, 2024 12:17 AM
> 
> Hi
> 
> Am 01.02.24 um 07:00 schrieb mhkelley58@xxxxxxxxx:
> > From: Michael Kelley <mhklinux@xxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxx>
> 
> Reviewed-by: Thomas Zimmermann <tzimmermann@xxxxxxx>

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;
> >   	}
> >
> >   	/*
>