[ipxe-devel] [PATCH 4/4] [virtio] Add virtio-net 1.0 support

[Michael S. Tsirkin]

On Fri, Mar 11, 2016 at 02:23:31PM +0100, Ladi Prosek wrote:
> On Fri, Mar 11, 2016 at 2:09 PM, Michael S. Tsirkin <mst at redhat.com> wrote:
> > On Fri, Mar 11, 2016 at 02:43:23AM +0200, Michael S. Tsirkin wrote:
> >> On Thu, Mar 10, 2016 at 04:04:31PM +0100, Ladi Prosek wrote:
> >> > On Thu, Mar 10, 2016 at 3:12 PM, Michael S. Tsirkin <mst at redhat.com> wrote:
> >> > > On Wed, Mar 09, 2016 at 07:20:03PM +0100, Ladi Prosek wrote:
> >> > >> +     /* Enable PCI bus master and reset NIC */
> >> > >> +     adjust_pci_device ( pci );
> >> > >
> >> > > At the moment, this enables memory and io unconditionally.  But I think
> >> > > it should check BAR is assigned before enabling and using it, since
> >> > > e.g. pci express devices might not have their BARs assigned.
> >> > >
> >> > > I'm also not sure 64 bit BAR values will work under ipxe -
> >> > > if not it's preferably to fall back on io or cfg access.
> >> >
> >> > Hmm.. 64-bit BARs are indeed not supported. It would be better to
> >> > always use the cfg cap then and remove all that BAR mapping business.
> >> > Less code and fewer assumptions for the win.
> >>
> >> Much slower though.
> >
> > Thinking more about it, I think it's a good idea to
> > leave the mapping infrastructure in place, but
> > maybe only do the CFG approach as the first step.
> >
> > Once code is upstream and works, we can add
> > faster BAR/IO support later.
> 
> Apologies for a naive question: since we need a 64-bit iPXE build for
> proper 64-bit BAR support, does it mean that we would have to ship two
> .rom files with QEMU, one for 32-bit guests and one for 64-bit guests?

Right - how does one handle 32 bit guests?

Maybe include both binaries in the rom, and add a wrapper selecting
the correct part of the ROM depending on the CPU?
1. start wrapper
2. check cpuid for 64 bit extensions
3. run 32 or 64 bit binary

A bit wasteful but rather easy to implement.

Did anyone try anything like this?

> > Cc Gerd who worked on similar issues for virtio blk.
> >
> > Gerd, what did you do there?
> >
> >> > > --
> >> > > MST