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

From: Helge Deller
Date: Fri Feb 09 2024 - 10:54:22 EST

On 2/9/24 16:23, Michael Kelley wrote:
From: Thomas Zimmermann <tzimmermann@xxxxxxx> Sent: Thursday, February 1, 2024 12:17 AM


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.

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.



drivers/video/fbdev/hyperv_fb.c | 2 --
1 file changed, 2 deletions(-)

diff --git a/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;