Re: [6.12.y regression] Regression with 58130e7ce6cb ("PCI/ERR: Ensure error recoverability at all times"): echo vfio-pci >driver_override does not work for DVB Adapter

[Alex Williamson <alex@shazbot.org>]

On Tue, 31 Mar 2026 15:09:34 +0200
Lukas Wunner <lukas@wunner.de> wrote:

> On Mon, Mar 30, 2026 at 08:14:53AM +0200, Bernd Schumacher wrote:
> > [    0.318903] pci 0000:07:00.0: [dd01:0003] type 00 class 0x048000 PCIe Endpoint
> > [    0.318939] pci 0000:07:00.0: BAR 0 [mem 0xfffffffffc500000-0xfffffffffc50ffff 64bit]  
> 
> BIOS initially sets the BAR address to an incorrect value (the top 32 bits
> should be all zeroes instead of all ones)...
> 
> > [    0.339685] pci 0000:07:00.0: BAR 0 [mem 0xfffffffffc500000-0xfffffffffc50ffff 64bit]: can't claim; no compatible bridge window  
> [...]
> > [    0.311065] pci 0000:02:03.0: [1022:57a3] type 01 class 0x060400 PCIe Switch Downstream Port
> > [    0.311107] pci 0000:02:03.0: PCI bridge to [bus 07]
> > [    0.311118] pci 0000:02:03.0:   bridge window [mem 0xfc500000-0xfc5fffff]  
> 
> ... this doesn't fit into the window of the bridge above the DVB card,
> which has the top 32 bits set to all zeroes...
> 
> > [    0.357346] pci 0000:07:00.0: BAR 0 [mem 0xfc500000-0xfc50ffff 64bit]: assigned  
> 
> ... the kernel fixes the incorrect BAR, but it seems there's an ordering
> issue such that pci_save_state() is called beforehand.  It's weird that
> this doen't occur with newer kernels and it would be good to understand why.
> I'm not seeing the ordering issue despite staring at the code for a while.

Do we know this isn't occurring on newer kernels?  If we have a bogus
BAR address that later gets fixed, this seems like a fairly unique
setup.  AIUI, we're saving the state via the call chain invoked by
subsys_initcall(pcibios_init), but I think we're doing the resource
fixes in fs_initcall(pcibios_assign_resources).  That suggests that the
saved state would have the bogus BAR values.

If we toss PM runtime into that mix, pci_pm_default_resume_early() will
call pci_restore_state() however pci_save_state() in that file is
mostly wrapped around pci_dev->state_saved guards.  This suggests we
likely won't save the reallocated state, but we will restore the
pre-reallocated state.

Maybe this can be quickly validated by loading vfio-pci with the
disable_idle_d3=1 option to avoid the PM transition.  Thanks,

Alex