Re: [virtio-dev] Re: [virtio] [PATCH] virtio-pci: access device using config

Paolo Bonzini <> writes:
> Il 05/11/2013 07:27, Rusty Russell ha scritto:
>> "Michael S. Tsirkin" <> writes:
>>> > VIRTIO-39.
>> We can discuss this on the call, but I don't like this.
>> 
>> PXE boot style environments will have to handle memory bars for modern
>> PCIE devices.  Why should virtio be special?
>
> Many devices these days do have some kind of backdoor to the memory
> BARs, through either config space or an I/O BAR.  AHCI even standardizes
> its backdoor with a special PCI capability.
>
> GPUs also have backdoors in order to support accesses to BARs from the
> VGA BIOS without knowing the allocation of the BARs.  Often the GPUs use
> a register in the VGA ports (0x3b0...0x3df) so that they can even access
> BARs correctly even if the OS has already accessed 0xcf8 but has not
> accessed 0xcfc yet.

Wow, I had no idea.  OK, let's offer this then...

Thanks,
Rusty.