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

[Auger Eric]

Hi Nicolas, Alex,

On 3/11/19 9:39 AM, Auger Eric wrote:
> Hi Nicolas,
> 
> On 3/10/19 11:06 PM, Nicolas Roy-Renaud 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
> 
> Last time I got this error was when a readw was attempted in
> pci_map_rom/pci_get_rom_size while the Device Control memory space
> access bit was disabled in PCI cfg space. At the time you attempt to
> dump the rom, the guest may have disabled this bit?

Sorry I missed your intermediate replies. So it looks the same issue.

Thanks

Eric
> 
> Thanks
> 
> Eric
>>
>> This isn't a recent thing, I started investigating this several months
>> ago
>> <https://www.reddit.com/r/VFIO/comments/971umf/is_everyone_else_getting_invalid_pci_rom_header/>
>> and it turned out that I wasn't alone: Everyone on the VFIO discord chat
>> who actually tried this got the same error message.
>>
>> The interesting part is that launching and shutting down a VM using that
>> device clears the issue and it then becomes possible to dump the ROM as
>> expected. I've known a number of issues with VFIO and ROMs can be
>> resolved either like this or by attaching the guest GPU on an already
>> live VM (for reasons I admittedly don't quite understand myself), but
>> since getting a ROM dump can be an important part of setting up the VM
>> that will receive the device in the first place, I don't know if this
>> could be considered an option.
>>
>> I figured this had something to do with the host BIOS tainting the ROM
>> on boot, which is a well known thing on boot GPUs (even though the one
>> I'm attempting to dump isn't), and that passing the tainted GPU to a VM
>> then causes the device to power cycle and clears that, somehow? With
>> that in mind, I've attempted a number of things, but neither resetting
>> the PCI port the device is attached to
>> <https://unix.stackexchange.com/a/474378>, nor doing function-reset on
>> the device, nor going in and out of sleep mode on the guest seems to
>> resolve the issue. I've also tried using pci-stub instead of vfio-pci to
>> see if this wasn't a driver issue, but no success here either.
>>
>> Is there anyone with better technical knowledge of VFIO who could help
>> with this?
>>
>> - Nicolas
>>
>>
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> 
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