Re: uefi secureboot vm and IO window overlap

[Bjorn Helgaas <helgaas@kernel.org>]

Hi Kallol,

On Fri, Dec 09, 2022 at 06:44:42PM +0000, Kallol Biswas [C] wrote:
> We are observing an io window overlap issue in a secureboot enabled uefi vm.
> 
> Linux displays:
> pci 0000:00:1d.0: can't claim BAR 4 [io  0x92a0-0x92bf]: address conflict with PCI Bus 0000:01 [io  0x9000-0x9fff]
> 
> Eventually conflict gets resolved but we need to understand why get the conflict in the first place.
> 
> Details:
> 
> The VM is a uefi based VM and the issue shows up if secure boot is
> enabled.  We have enabled ovmf log and uefi/ovmf programs a bridge
> IO window with the range 0x9000-0x91ff, but in Linux we see the same
> bridge is programmed with 0x9000-0x9fff. This results in an address
> conflict with subsequent devices.

Linux normally doesn't reassign bridge windows if the existing
configuration (typically from firmware) works.

Booting with "pci=earlydump" should dump the config before Linux
touches anything.

I see your response about being able to reproduce it where it's easier
to debug.  If you need more help, please include the complete dmesg
log so we can see what's happening.

Bjorn