[Qemu-devel] Re: [PATCH 0/2] fix virtio_blk serial pci config breakage

[Anthony Liguori]

Avi Kivity wrote:
> On 09/29/2009 03:51 PM, Anthony Liguori wrote:
> > > The change this patch implements is passing of the
> > > identify data through a mapping established by
> > > PCI BAR #5 rather than the PCI config area, the
> > > latter of which resulted in the above breakage.
> >
> >
> > This is a massive layering violation.  The virtio-blk ABI cannot make 
> > demands of the transport.
>
> True.
>
> > The better solution would be to move the entire virtio-pci config 
> > space to a separate BAR that's an MMIO region.  Then there is no 
> > practical limit on the size of the config area.
>
> Don't some fast-paths accesses go through the config space?  Using 
> mmio will slow them down.

Not that I know of.

Regards,

Anthony Liguori