[vfio-users] "Invalid PCI ROM header signature: expecting 0xaa55, got 0xffff" when attempting to dump PCI ROM

[Alex Williamson]

On Sun, 10 Mar 2019 18:06:37 -0400
Nicolas Roy-Renaud <nicolas.roy-renaud.1 at ens.etsmtl.ca> wrote:

> I've seen a lot of people before reccomand VFIO newcomers to flash their 
> GPU if they couldn't get their passthrough working right before, and 
> since I know how potentially risky and avoidable this sort of procedure 
> is (since QEMU lets you just pass your own ROM to the VM to be used 
> instead), and while attempting to go through the steps myself 
> <http://vfio.blogspot.com/2014/08/does-my-graphics-card-rom-support-efi.html> 
> (even though I've had a working VFIO setup for years), got something 
> unexpected.
> 
> Attempting to dump the ROM from my guest card _/freshly /_/_after a 
> reboot_/ results in the following error message :
> 
> cat: '/sys/bus/pci/devices/0000:07:00.0/rom': Input/output error
> 
> Accompanied by the following like in dmesg :
> 
> [ 1734.316429] vfio-pci 0000:07:00.0: Invalid PCI ROM header signature: expecting 0xaa55, got 0xffff

If lspci for the device reports:

        Control: I/O- Mem- BusMaster- ...

(specifically Mem-), this could be the reason it's failing.  The PCI
ROM BAR is a memory region and memory decode needs to be enabled on the
device in order to get access to it.  Also if you have the device
already bound to vfio-pci, the device might be in a D3 low power state,
which could make that memory region unavailable.  You can use the
'enable' file in sysfs to fix both of these, so your sequence would
look like this:

echo 1 > /sys/bus/pci/devices/0000:07:00.0/enable
echo 1 > /sys/bus/pci/devices/0000:07:00.0/rom
cat /sys/bus/pci/devices/0000:07:00.0/rom > gpu.rom
echo 0 > /sys/bus/pci/devices/0000:07:00.0/rom
echo 0 > /sys/bus/pci/devices/0000:07:00.0/enable

Thanks,
Alex