> From: Michael Kelley <[email protected]>
> Sent: Sunday, April 5, 2026 4:13 PM
> > ...
> > 96959283a58d adds "select SYSFB if !HYPERV_VTL_MODE", but we can
> > still manually unset CONFIG_SYSFB (I happened to do this when debugging
> > the kdump issue), and hv_pci won't work.
>
> Just curious -- how would you manually unset CONFIG_SYSFB? The kernel
> makefile always resync's .config against the Kconfig rules, which would add
> CONFIG_SYSFB back again. The Kconfig files essentially say that removing
> CONFIG_SYSFB is an invalid configuration.
Sorry, my description above is wrong: on the mainline kernel that has
96959283a58d ("Drivers: hv: Always select CONFIG_SYSFB for Hyper-V guests"),
I'm unable to unset CONFIG_SYSFB.
When I was able to unset CONFIG_SYSFB, I was actually on Ubuntu 22.04
(Ubuntu-azure-6.8-6.8.0-1049.55_22.04.1, released in Feb 2026). I thought the
kernel has 96959283a58d, but actually it doesn't...
> > IMO vmbus_reserve_fb() should unconditionally reserve the frame buffer
> > MMIO range. I'll post a patch like this:
> >
> > --- a/drivers/hv/vmbus_drv.c
> > +++ b/drivers/hv/vmbus_drv.c
> > @@ -2395,10 +2398,8 @@ static void __maybe_unused
> vmbus_reserve_fb(void)
> >
> > if (efi_enabled(EFI_BOOT)) {
> > /* Gen2 VM: get FB base from EFI framebuffer */
> > - if (IS_ENABLED(CONFIG_SYSFB)) {
> > - start = sysfb_primary_display.screen.lfb_base;
> > - size = max_t(__u32,
> > sysfb_primary_display.screen.lfb_size,
> 0x800000);
> > - }
> > + start = sysfb_primary_display.screen.lfb_base;
> > + size = max_t(__u32, sysfb_primary_display.screen.lfb_size,
> 0x800000);
Please ignore the change above.
> On arm64 the existence of sysfb_primary_display is conditional on
> several config variables, including CONFIG_SYSFB and CONFIG_EFI_EARLYCON.
> (see drivers/firmware/efi/efi-init.c) If you can take away CONFIG_SYSFB, you
> could also take away CONFIG_EFI_EARLYCON and end up with build error on
> arm64. So I'm not clear how this approach would be more robust against
> invalid .config changes.
Agreed. Then let's keep vmbus_reserve_fb() as is.
Thanks,
Dexuan
