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

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Message-ID: <8f6efa96-0744-4313-bb15-b38a992e05fc@gmx.de>
Date: Fri, 9 Feb 2024 16:53:37 +0100
From: Helge Deller <deller@....de>
To: Michael Kelley <mhklinux@...look.com>,
 "wei.liu@...nel.org" <wei.liu@...nel.org>
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()

On 2/9/24 16:23, Michael Kelley wrote:
> 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.

I'm fine with either.
If there is an upcoming hyper-v pull request, I'm fine if this is included
there. If not, let me know and I can take it via fbdev.

Helge



>
> 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;
>>>    	}
>>>
>>>    	/*
>>
>
>